Animalcule, a diminutive term (from the word animal), applied by naturalists to those minute beings which become apparent in various fluids when subjected to the microscope. They were named infusory animals (Infusoria) by Müller, one of the most celebrated observers in this department of zoology; and the appellation, however inapplicable, now occurs in the majority of scientific publications. Of course it applies with propriety only to such species as are developed through the medium of infused substances. Now we know, that of 400 species of Infusoria (commonly so called) described by Müller himself, not a sixth part were observed in any kind of infusions; whilst the remainder inhabited the most translucent waters, and speedily died when placed in impure or corrupted liquids. Even the word animalcule (or little animal) does not convey a positive or sufficiently restricted idea in relation to this particular class; because mites and certain polypi are extremely minute in their dimensions, and equally require the aid of microscopical investigation; and thus the term microscopics (microscopiques), recently proposed by M. Bory de St Vincent, is not less faulty than its predecessors. The size of an animal, in fact, bears no essential relation to the other conditions of its organization; and therefore we cannot infer its nature with any certainty from a knowledge of its dimensions. At the same time it must be admitted, that the most simply organized, both of plants and animals, are also the most minute; and thus the Infusoria may be regarded as possessed of certain characters in common. We here adopt the word Animalcule, chiefly because it is the most familiar to the English reader.

The subjects of our present observations may be thus defined:—Animals invisible to the naked eye;1 more or less translucent; unprovided with members (the caudal, and other appendices, with which certain species are furnished, being scarcely regardable as such); no perceptible eyes; contractile in whole or in part; endowed with the sense of touch; deriving nourishment by absorption; generation (when not apparently spontaneous, and consequently incomprehensible) effected by division, or by the emission of gemmules or oviform bodies; inhabitants of liquids. They are the smallest and most simple of living creatures, but not less perfect than the other tribes; for though they possess the fewest faculties, their means are in every way adequate to their wants, and their vital energies proportioned to their sphere of enjoyment.

Among microscopical animals we find many species which, in their aspect and structure, present no analogy

---

1 The Volvox globator, and a few others, which are just discernible without the aid of a microscope, form exceptions to the above character. to other forms of animal life; they are merely moving molecules of the simplest organization, the exact nature of which it is sometimes difficult to determine, and which involve in deeper obscurity the mysterious line of demarcation by which we so often seek in vain to separate the animal from the vegetable kingdom. If, however, the true distinction between plants and animals consists chiefly in the irritability and power of contraction possessed by the latter, then the Infusoria, which are strongly endowed with these attributes, are indeed so far removed from the vegetable kingdom, that the name of Zoophytes, or animal plants, is inapplicable to the class to which they belong. In the extreme simplicity of their structure, they no doubt present some analogy to the least complicated tribes of plants, such as the algae and others; but it is a mere analogy, and not a connection of affinity,—for no alliance between these kingdoms has ever been demonstrated, although certain obscure phenomena may have presented difficulties in the way of our investigations. "We need not be surprised," Mr Macleay observes in his *Horse Entomology*, "that several of the Linnaean algae should be still hovering in a state of uncertainty between the two kingdoms; but, on the contrary, be prepared to expect additional proofs of the analogy which the two great divisions of organized matter bear to each other. The Agastrica, or Agastraires of De Blainville, are indeed animals, though they have neither distinct organs of sense, alimentary canal, nor even mouth,—though they have, in short, so far as our present knowledge of them would lead us to believe, no internal digestion whatever to execute, but trust for nourishment, like plants, to the absorption of their external pores. They must be esteemed animals on account of their peculiar irritability; but are vegetables in almost every other respect."

Our knowledge of the history of animalcules resulted from the improvement of the microscope by Hartzocker and Leeuwenhoek. The ancients were consequently unacquainted with the mysteries of this "invisible world;" and we are thus saved the tedium of a lengthened bibliographical investigation. Notwithstanding the observations of Hill, Baker, Ledermuller, Goeze, Gleichen, Roësel, Pallas, Needham, Spallanzani, and several other minute and laborious inquirers, it may be said that this branch of zoology only assumed a truly scientific form in consequence of the labours of a distinguished Danish naturalist, Otho Frederic Müller. His earlier works, such as the *Vermium Terrestrium et Fluviatilium Historia*, and the *Zoologia Danicae Prodromus*, presented very decided improvements in the knowledge and classification of animalcules. These emendations were transferred by Gmelin to the 13th edition of the *Systema Naturae* of Linnaeus, in which animalcules form the fifth order of the class of Vermes. But the work which had the rest been wanting, would alone have immortalized the name of Müller, appeared (posthumously) in 1786, under the title of *Animalcula Infusoria, Fluviatilia et Marina*. It is illustrated by 50 plates, containing figures of 360 species variously represented. A later and very useful compendium of knowledge regarding microscopical animals forms a portion of the *Encyclopédie Méthodique* (46th livraison), in which Bruguière has reproduced the plates of Müller, with the addition of several others of equal accuracy from the third volume of Roësel's *Insectes-bélistigüen*. The reader will there find descriptions of 28 plates, containing nearly 1100 figures representing 385 animalcular species.

Before proceeding further, we shall present a brief view of the system of Müller, as of high importance in itself, and the fundamental basis of the more recent and improved arrangements. It includes, however, several genera which are not now classed among the animalcular tribes. He divides the Class of Animalcula Infusoria as follows:

**Order I.—No External Organs.**

- **Thickened.** - Genus 1. *Monas*: body punctiform. 10 species. - Genus 2. *Proteus*: body variable. 2 species. - Genus 3. *Voleox*: body spherical. 12 species. - Genus 4. *Enchelis*: body cylindrical. 27 species. - Genus 5. *Vibrio*: body elongated. 31 species.

- **Membranous.** - Genus 6. *Cyclidium*: body oval. 10 species. - Genus 7. *Paramecium*: body oblong. 5 species. - Genus 8. *Kolpoda*: body sinuous. 16 species. - Genus 9. *Gonium*: body angular. 5 species. - Genus 10. *Bursaria*: body excavated. 5 species.

**Order II.—External Organs.**

- **Naked.** - Genus 11. *Cercaria*: smooth, tailed. 22 species. - Genus 12. *Trichoda*: haired or ciliated. 89 species. - Genus 13. *Kerona*: with horny appendices. 14 species. - Genus 14. *Himantopus*: with ciliated appendices. 7 species. - Genus 15. *Leucophora*: the entire surface ciliated. 26 species. - Genus 16. *Vorticella*: orifice ciliated. 75 species.

- **Furnished with a Shell.** - Genus 17. *Brachionus*: orifice ciliated. 22 species.

In the year 1815 Lamarck published the first part of his *Animaux sans Vertèbres*, a work which forms an epoch in the history of the inferior tribes. In this signal publication the author adopts a different course from that usually followed by systematic writers; and pursuing an ascending rather than a descending scale, he commences with the lowest and least complex species, viz. the Infusoria. From this class, however, he rejects all those species in which any kind of complication of organs is apparent. All the genera so distinguished are referred by him to the first order of the second class of the animal kingdom, called Polypi, under the title of *Polypi ciliati*; and the true and restricted Infusoria are thus defined: *Microscopical animals, gelatinous, transparent, polymorphous, contractile; having no distinct mouth, nor constant, determinable, internal organs; generation fissiparous or sub-gemmiparous*. The genus Kerona, it may be further remarked, is in this system united to the Himantopus of Müller, while the genus Cercaria of that author is divided into two. Thus the class Infusoria of Lamarck, composed of two great sections, the naked and the appendicated, may be said to correspond to the first 14 genera of the Danish naturalists.

Cuvier, in the *Règne Animal* (1817), places the Infusoria as a part of his fourth great division, the zoophytical or radiated animals. The term *radiated* was originally bestowed on a numerous tribe of animals, such as the Asterns and others, on account of their arms or tentacula being extended in a radiated or star-like form; but it certainly applies unfitly to the true Infusoria of Lamarck, which possess nothing resembling a radiated structure. It cannot, however, be always expected that a general term of wide import should apply with etymological accuracy to every part of the extensive series which it is intended to embrace. Cuvier then divides his Infusoria into two orders, *Les Rotifères*, and *Les Infusoires homogènes*, the former of which correspond to the ciliated polypi of La- According to M. de Blainville, the class Infusoria can scarcely be regarded as established upon a natural foundation. The organization of its component tribes is so various as to lead to the belief that a more precise knowledge would show that several of those tribes belong to different types of the animal kingdom. Some, as the genus Brachionus, are symmetrically formed both as regards their bodies and appendages, and are protected by a horny or crustaceous covering. Others, as Vibrio, Paramacium, &c. have the body elongated, depressed, vermiform, and without appendages. A third division exhibit a radiated structure, as for example the Vorticellar, which, however, we have already stated, are now seldom classed among the Infusoria. Many genera, such as Proteus, Volvox, Monas, are amorphous, or without determinate form, and cannot be referred to any other known type of the animal kingdom. They are regarded by many as the elementary molecules of all animal life, and in their structure no other than the cellular tissue is observable. They may be said to be dependent on external circumstances, instead of being able, like other animals, to modify or control them; and their usually spherical form is the necessary result of an equal pressure of water on all sides of a frail and yielding texture. M. de Blainville considers the genera Brachionus, Ureclaria, Cercaria, Furlaria, Kerona, Trichocerca, and Himantopus, as belonging to the type of Entomozoaires or articulated animals, and especially to the class Heteropoda, order Entomotracea. Many species of Vibrio he regards as Apodes, as well as Paramacium and Kolpoda. Other species of the genera Vibrio and Cyclidium ought rather to be ranged with the Planaria; and in the genus Leucophra there is even a species which M. de Blainville is inclined to look upon as an Ascidia! Finally, the genera Goniom, Proteus, Poleax, and Monas, if they are really animals, appear to form a distinct type, which may be called Amorphes or Agastraeans; so named from the circumstance of their having neither determinate form nor reduplication of the external envelope for the formation of a stomach, as in all other true animals.

Such is a brief exposition of the views of one of the most distinguished physiological inquirers of the present day. It may serve, if for nothing more, at least to show the unsettled state of opinion concerning these extraordinary creatures. In regard to this, however, we may rest assured that, in the future progress of science, the class Infusoria, as at present constituted, will suffer an entire dismemberment, and its component parts will be referred to various groups of the animal kingdom, some of them widely distant from each other.

In the year 1826 a full and most elaborate classification of microscopical animals was given to the world by M. Bory de St Vincent. As it is the singular mode of existence of animalcular beings, their general economy in the field of nature, the actual conditions of their organization, and the state of their limited faculties so far as these can be ascertained, with which we are chiefly interested—so, in our systematic view of this extraordinary class, we shall merely present to our readers the characters of the principal genera, and of a few of the most remarkable species which they contain. But, as some may be desirous to possess at least a sketch of the full extent and condition of this intricate subject, we have constructed the accompanying tabular scheme of the orders, families, and genera of microscopical animals, according to the views of M. Bory de St Vincent, the latest and most assiduous writer on this department with whose labours we are acquainted. We have thought it advisable to retain the terms of the original language, lest, by inadvertence or misconception on the part of the translator, any additional obscurity should rise around a subject already sufficiently encumbered. (See Tabular View on the next page.)

The order Gymnodes of Bory de St Vincent nearly corresponds to the entire class Infusoria of Lamarck; and although the observations by which he illustrates his arrangement partake of the accustomed defects of the French philosophy, the facts which he details, if not the theoretical views which he inculcates, are worthy of an attentive consideration. These mysterious creatures are observed to swim with astonishing rapidity; and although their bodies are usually diaphanous, it has hitherto proved impossible, even by the aid of the most powerful glasses, to ascertain by what natural mechanism these movements are effected. They direct their courses by a discretionary power, in one direction rather than another, avoiding and turning round opposing obstacles, according to the necessities of the case—discerning, as the process of evaporation proceeds, the points in which they may prolong their existence, and flocking in crowds to those places where they are best screened from the overpowering brilliancy of the reflecting mirror. They thus appear to possess volition, which we are accustomed to regard as a result dependent on the faculties of perception and comparison.

The principal obstacle to our understanding the essential nature of animalcules results from their want of a nervous system, which, in ourselves, and in all the intermediate classes of the nature of whose consciousness we have even a vague idea, we regard as the sine qua non of sensation and intelligence. Voluntary motion without muscular action is also a circumstance which we cannot very clearly comprehend. But as there may be "more things in heaven and earth than are dreamt of in our philosophy," we must not reject facts, that is to say appearances which present themselves under the same determinate and uniform aspect to various unprejudiced observers, merely because they do not coincide, or may possibly controvert or interfere, with a previous hypothesis. On the other hand, the extreme softness of texture, and excessive minuteness, of most of the animalcular species, render anatomical investigation almost impossible; and naturalists may have erred in supposing the absence of what they are merely unable to perceive and demonstrate.

It is in truth impossible to discover any traces of the nervous system, even among several tribes of animals in other respects much more highly organized than the subjects of our present inquiry. Trembley's examination of the Polypus threw no positive light upon the matter; nor did Gade's dissections of the larger Meduse enable him to discover either muscular or nervous fibres. According to M. Bory de St Vincent, the nervous system is one of the last to be developed. To the perfect simplicity of the Monads, the first perceptible addition is that of a central cavity, or rudimentary intestinal sac, which we find to occur even before the existence of a mouth. Next appears an opening to this canal, which serves both for the reception of nourishment, and the rejection of excrementitious parts where such exist. The hairs and cirrated appendages which ensue in still more complicated species have been regarded as the early rudiments of the respiratory system; and even a heart, or central organ of a circulating fluid, is partly developed before the appearance of any nervous chords. The earliest, most general, and perhaps the only indispensable function of animal life, is that of nutrition. But the materials of nutrition are so different, and their modes of reception so various, that the exercise of this TABLE OF THE ORDERS, FAMILIES, AND GENRES OF ANIMALCULES, according to a new Analytical Method. By Bory de Saint-Vincent.

| ORDRES | FAMILLES | GENRES | |----------------------|---------------------------|----------------------| | | | | | **GYMNODÈS** | | | | Légèrement ébrasées, sans elle ni elles visibles.. | | Un seul appendice essentiel terminal. | | Genre animaux superficies en forme de héron frétant. | | Ol. Q. câyeux chevauchant ou de deux appendices et leur correspondance dans une ou flere espèces identiques ou apparentées. |

**PARENTHÈSÉES**

Oui. L'œil répand des eaux froides la surface de cette lumière est le plus clair et le plus flou des deux résultats.

**MICROSCOPIQUES**

Musées de cette ère géologique appartenant à des êtres vivants très anciens. function by no means necessitates the existence of a mouth, a stomach, or an alimentary canal; for an increase of parts may be effected even through the medium of imponderable or elastic fluids, and by imperceptible and superficial pores.

The exterior of an infusory animal may be compared to the interior of one of the higher classes, in which nutrition is carried on by the reception of the chyle by the absorbent pores. These pores are external among the Infusoria, and the process of absorption is with them analogous to that of plants, in which there is a direct reception and appropriation of fluids from the earth and air, without any previous preparation in a central cavity or stomach. Zoophytes in general have indeed been called the cryptogamia of the animal kingdom. According to Carus, the Infusoria ought to be regarded merely as little cells, partially filled with lymph, and possessed of the powers of nutrition and locomotion; and thus the infinite changes and variations perceptible in their forms may be supposed to be produced by the various degrees in which this fluid is collected at one or other of the points of their bodies. In the opinion of that anatomist, a more complete development of the organs of motion, and indeed of the whole organization, is inseparably united with the appearance of a distinct nervous system. This may be true as a general rule, but not as a universal principle; for the Medusa has more apparent voluntary motion than the Asterias, though the former is destitute of those nerves which in the latter make their first appearance in the shape of a pale thread-like ring surrounding the oesophagus. It is this ring around the upper extremity of the alimentary canal which, in the molluscous and articulated classes, we shall afterwards find to constitute the most uniform and most essential portion of the nervous system. The Medusæ, just referred to, being almost of the same specific gravity with water, are easily carried by currents, and moved about from place to place by the action of the waves, or even (as in the case of Holothuria physalis) by the winds; but Carus and other writers have assuredly erred in doubting that they execute a voluntary locomotion; for that they do so in a very decided and graceful manner must be obvious to all who have attended to these animals in their native haunts along the shores, or among the land-locked waters of the beautiful firths of Scotland.

The mysteries revealed by the glasses of Leeuwenhoek were at first regarded as beyond belief. The uncertainty of microscopical investigations, in consequence of which so much was supposed to depend on the imagination of the beholder, was alleged against them; and even at an after-period, when men of sober judgment and the most industrious application had confirmed the experience of the indefatigable Dutchman, the wit of Voltaire did not disdain to throw its cutting sarcasm over the disciples of the "anguilles de la pâte et du vinaigre." We hope it is now admitted, that however frequently those who endeavour to expound the mysteries of nature may fail in their attempts at elucidation, yet that there is nothing in the manifold works of Omnipotent Wisdom which, if duly studied and rightly understood, would not conduce to our wellbeing and happiness; and that a single square inch of water, with its many millions of animalcular atoms, is in truth as wonderful a work of divine intelligence, and as interesting a field for human investigation, as the starry galaxy of heaven.

In tam parvis, atque tam nullis, qua ratio! Quanta vis! quam inextricabilis perfectio! And if a heathen philosopher (Pliny) has so expressed his almost reverential admiration, is it not to be deplored that those whose labours might be carried on under the influence of a purer light, seem as often degraded as exalted by the contemplation of their Creator's works; and, referring all to the powers of nature, or some other indefinite abstraction, refuse to recognise, amid so many wonders, the "Good Supreme" from whom these and other mightier wonders have proceeded? It is in the study of the subject with which we are now engaged, and the analogous pursuits of physiology, where the completion of the most perfect design and the happiest results of superhuman forethought are so constantly manifested, that we frequently meet, where we should least expect it, with the sneer of the sceptic, or the impious ridicule of the unbeliever. How different are the sentiments of one who combines the piety of the Christian with the genius of the poet and philosopher. "But about the time of its invention (the invention of the telescope), another instrument was formed, which laid open a scene no less wonderful, and rewarded the inquisitive spirit of man with a discovery which serves to neutralize the whole of this argument. This was the microscope. The one led me to see a system in every star; the other leads me to see a world in every atom. The one taught me that this mighty globe, with the whole burden of its people and of its countries, is but a grain of sand on the high field of immensity; the other teaches me that every grain of sand may harbour within it the tribes and the families of a busy population. The one told me of the insignificance of the world I tread upon; the other redeems it from all its insignificance; for it tells me, that in the leaves of every forest, and in the flowers of every garden, and in the waters of every rivulet, there are worlds teeming with life, and numberless as are the glories of the firmament. The one has suggested to me, that beyond and above all that is visible to man, there may lie fields of creation which sweep immeasurably along, and carry the impress of the Almighty's hand to the remotest scenes of the universe; the other suggests to me, that within and beneath all that minuteness which the aided eye of man has been able to explore, there may be a region of invisibles; and that, could we draw aside the mysterious curtain which shrouds it from our senses, we might then see a theatre of as many wonders as astronomy has unfolded, a universe within the compass of a point so small as to elude all the powers of the microscope, but where the wonder-working God finds room for the exercise of all his attributes, where he can raise another mechanism of worlds, and fill and animate them all with the evidence of his glory."

Although we cannot hope to derive the same amusement or advantage from the study of each of the animalcular species considered separately, as we do from the consideration of the history of many of the higher animals, yet, in a philosophical point of view, a knowledge of the general attributes of the class presents several highly important objects; and their obscure origin, their singular organization, and more singular mode of existence, cannot fail to excite our unfeigned wonder and admiration. They can scarcely be described otherwise than by a negation of all those characters which constitute the life, power, and activity of other beings; they have no head, no eyes, no muscles, no blood-vessels, no nerves, no determinate organs for respiration, generation, or digestion—and yet they are endowed with life.

The animal nature of the Infusoria has indeed been denied by many; but such is the regular gradation from the most simply organized of the monadial forms to the much

---

1 Chalmers's Astronomical Discoveries, p. 112. more complicated structure of the Polypi, which present, under a remarkable aspect, such unequivocal characters of animality, that it is impossible to draw the line of demarcation; and if we admit the life of the one we can scarcely doubt that of the other. Yet many of the Infusoria appear to present the very lowest conceivable point to which animal life can be reduced.

The structure of an animal, the individual existence of which is preserved by the absorption of a circumambient fluid, and the continuance of whose species is effected by the division or separation of a part of its own body, might, *a priori*, be supposed to be of the most simple kind. "We may rest assured," observes Lamarck, "that whenever an organic function is itself unnecessary, the special organ by which it is usually performed will not be found to exist." It is indeed by considering the nature of the Infusoria that we are enabled to form a proper idea of the simplest condition of animal life; and the invention of the telescope was not of higher importance to the astronomer, than that of the microscope to the physiological naturalist. There are few subjects of reflection more interesting than the uses which philosophers of an enlightened age have deduced and matured from the scanty knowledge of a barbarous people. Glass, a material known at an early period to the Asiatic nations, and once estimated at its weight in gold, has become in the hands of Europeans of more value than the finest gold. Whoever polished the first lens may be said to have laid the foundation of an instrument destined to discover thousands of celestial worlds above and around us, and an unseen world of wonders beneath our feet. "Indeed," says Cuvier, "it could not be expected that those Phoenician sailors who saw the sand of the shores of Bactria transformed by fire into a transparent glass, should have at once foreseen that this new substance would prolong the pleasures of sight to the old; that it would one day assist the astronomer in penetrating the depths of the heavens, and in numbering the stars of the milky way; that it would lay open to the naturalist a miniature world as populous, as rich in wonders, as that which alone seemed to have been granted to his senses and his contemplation; in fine, that the most simple and direct use of it would enable the inhabitants of the coast of the Baltic Sea to build palaces more magnificent than those of Tyre and Memphis, and to cultivate, almost under the frost of the polar circle, the most delicious fruits of the torrid zone."

The faculties of the most simple infusory animals, it has been observed, are reduced to such as are common to all living beings, and to that irritability which results from their animal nature; and their bodies are destitute of special organs, precisely because their extremely limited faculties neither require nor admit of such organs being exercised. The chief interest to be derived from the study of this class of beings results, according to Lamarck, from the view with which such study presents us of the ultimate point to which the organization of an animal is capable of being reduced; and, among all the wonders of the creation, he regards as the most surprising the existence of animal life in such inconceivably frail and simple bodies as the least complicated of the animalcular species. It is not, however, to be said that "nature was incapable of forming special organs from the materials of these frail gelatinous bodies," but rather that the all-wise Author and Ruler of Nature has seen fit to form them in what to us may appear a destitute and incomplete condition, merely because their structure does not fulfil those other conditions which, erroneously, we have sought to establish as the indispensable bases of Animal life. They truly show how confined a knowledge our limited faculties enable us to gain of His unlimited power; for they not only present no analogy to other more accustomed forms of life, but almost seem to exist in direct opposition to those laws in accordance with which we "live, move, and have our being."

Infusory animals, commonly so called, are found in the fresh and saline waters of all countries. They occur both naturally, if we may use the term in a contradistinctive sense, and as the apparent result of infused animal and vegetable substances. According to Leeuwenhoek, the milt of a cod-fish contains more animalcules than there are individuals of the human race existing on the face of the earth; and he calculated that 10,000 might be held within the bulk of a grain of sand. The size of many bears the same relation to that of a mite as the dimensions of a bee do to those of an elephant; and the most powerful microscopes frequently discover nothing more than merely perceptible points in motion. Flour and water made to the consistence of book-binders' paste, exposed in an open vessel, and frequently stirred to prevent the surface from growing hard, will in a few days be found to contain millions of animalcules. The thin pellicle which grows on the surface of an infusion of common black pepper also produces an innumerable congregation of minute beings. Of these and others the real origin is still exceedingly obscure; and both Müller and Spallanzani maintained the improbable opinion that they fell from the air. Their subsequent increase or multiplication is obviously effected in different and very singular ways. Such as are spherical are usually propagated by minute portions, which, though they burst from the anterior of the animalcule itself, cannot be called eggs; and such as are of a depressed or flattened form continue their race by cuttings or divisions of their own bodies. We first observe a line or groove, longitudinal or transverse, according to the species; and ere long a notch or incision is perceptible at one or other or both of the ends of that apparent line. This notch increases across or longitudinally, till at last a portion is separated or cut off, or the original animal is divided into two, and each assumes the form and nature of their mutual predecessor. These new objects retain for some time their natural shape, and then in their turn give rise to one or more individuals by a similar separation of parts. Lamarck seems to be of opinion (*Philosophie Zoologique*, tome ii. p. 120 and 150) that this multiplication by division, and that by the emission of gemmules or ovifrom portions, are modifications of one and the same natural process—that substantially each is the result of an extension and separation of parts, which take place when the parent individual has reached the final term of its increase. It is in fact the same excess of nourishment and growth of particular parts that, even in the higher classes, give rise to the germ of separate life, physically considered, although in regard to these the additional process of fecundation is required. It is the new light which may be gathered from the observation of the minutest of the animalcular tribes that renders their study both interesting and important to the physiologist; and it is the belief of some, that a persevering study of the history of microscopical animals will one day enable us to withdraw the mysterious veil which still conceals from our view the most important secrets of nature.

The systematic arrangement of animalcules which we propose to follow in this place is nearly that of Lamarck,

---

1 Réflexions sur la Marche actuelle des Sciences, &c., read to the Institute of France in April 1816. which is itself founded on the systems of Müller and Bruguière. The French naturalist includes in his system only such species of the same class described by Müller as are destitute of a mouth.

**ORDER I.—NAKED INFUSORIA.**

*Body extremely simple, apparently homogeneous, unprovided with organs or external appendages.*

The naked Infusoria are the smallest and simplest of those animals which are cognizable by the senses of man. When we expose water to air and light, especially if it contains an infusion of animal or vegetable remains, we speedily perceive, by the assistance of the microscope, a variety of animalcules. These are divided into two sections.

**SECTION I.—BODY THICK.**

*Of this section the bodies present such a perceptible degree of thickness as removes them from the simply membranous state.*

**GENUS MONAS.**—Body extremely small, of the simplest construction, transparent, punctiform.

The Monads are the smallest and least organized of living creatures. We have indeed scarcely any proof of their animal life, except that they are moving corpuscles, allied to the genus Volvox, the animality of which is undoubted. They have neither mouth nor alimentary canal, nor any apparent organs. They live by absorption, and are found in tranquil, but rarely in limpid waters. They are produced in infusions of animal and vegetable substances.

*Sp. 1. Monas termo.*—An extremely minute gelatinous point, scarcely perceptible even with the aid of a powerful lens, and frequently disappearing under a strong light in consequence of its perfect transparency. This species is common in ditch-water, and in numerous infusions. See Plate XLII. fig. 1. These minute creatures being the earliest discernible evidence of animal life, and the last result to which the higher and more perfect forms can be reduced by infusion, have been called the alpha and omega of all organized existence. Their history has given rise to many curious views, and more absurd speculations.

*Sp. 2. Monas atomus.*—White, with a variable dark-coloured spot, which appears to change its position. This species was found in sea-water which had been kept an entire winter, but was not very fetid. See Plate XLII. fig. 2 and 3.

*Sp. 3. Monas punctum.*—Nearly black, of a sub-cylindrical form. Found in the infusion of the pulp of a pear.

*Sp. 4. Monas lens.*—Hyaline, of an ovoid form. Found in all kinds of waters. Multiplies by spontaneous incision.

*Sp. 5. Monas puliciculus.*—Hyaline, with a greenish margin. Found in the waters of marshes. This species has been lately regarded as an *enchelis*. Indeed, so great is the difficulty of microscopical investigation, and such indefatigable patience is required in order to see things as they really are, that the species and genera of this class of beings are frequently transposed and altered in their relative position and arrangement, in consequence of the very dissimilar views which different observers have taken of the same object.

As it would be inconsistent with our present limits to describe more than a few species of each genus, we shall content ourselves with the preceding Monads. "How many kinds," observes Mr Adams, "there may be of these invisibles, is yet unknown, as they are discerned of all sizes, from those which are barely invisible to the naked eye, to such as resist the force of the microscope, as the fixed stars do that of the telescope, and, with the greatest powers hitherto invented, appear only as so many moving points."

**GENUS VOLVOX.**—Body very simple, transparent, spherical or ovoid, revolving on itself as on an axis.

With the exception of one species (*V. globator*) the volvoces are invisible to the naked eye. Under the microscope they assume the aspect of small gelatinous masses, which sometimes present an oval form. In some the body seems composed of numerous smaller globules united in one common mass. There is reason to suppose that these interior bodies are afterwards propelled outwardly, and become separate individuals. The species occur both in fresh and salt waters, and in vegetable infusions. They derive their generic name from the manner in which they turn or revolve upon their axis. Leeuwenhoek describes an animalcule "a thousand times smaller than a louse's eye, which exceeded all the rest in briskness," and turned itself round as it were upon a point, with the celerity of a spinning-top. The genus is divisible into two sections.

**Interior of the body apparently simple and homogeneous.**

*Sp. 1. Volvox punctatum.*—Spherical, blackish, with a central lucid point. Of this species many are sometimes seen together in their passage through the water. They occasionally move as if subjected to the influence of a whirlpool, and then separate. Numerous in fetid water.

*Sp. 2. Volvox granulum.*—Spherical, green, periphery hyaline. Dwells in the water of marshes.

*Sp. 3. Volvox globulus.*—Globular, sub-obscure behind. This species is ten times larger than the Monas lens. It occurs in most vegetable infusions, and moves with a slow fluttering motion. Plate XLII. fig. 4.

**Interior of the body exhibiting smaller corpuscles.**

*Sp. 4. Volvox pilula.*—Spherical, with greenish internal globules. In those pure waters which nourish the *Lemna minor*. Plate XLII. fig. 5.

*Sp. 5. Volvox lunula.*—Roundish and transparent, and composed of an innumerable assemblage of homogeneous crescent-shaped molecules, without any common margin. Its movements are of two kinds, that of the molecules among themselves, and that of the whole revolving mass. It occurs in marshy places in the early spring. Plate XLII. fig. 6.

*Sp. 6. Volvox globator.*—Commonly called the globe-animal. Spherical, membranous, the internal globules distant or scattered. Abundant in the infusions of hemp and tremella, and in stagnant pools during spring and summer. The following is an account of it by Mr Baker. "There is no appearance of either head, tail, or fins, and yet it moves in every direction, backwards, forwards, up or down, rolling over and over like a bowl, spinning horizontally like a top, or gliding along smoothly without turning itself at all; sometimes its motions are very slow, sometimes very swift; and, when it pleases, it can turn round as upon an axis very nimbly, without moving out of its place. The body is transparent, except where the circular spots are placed, which are probably its young." Another authority states that this species is at first very small, but increases to such a size that it may be discerned by the naked eye, and that its interior is filled with small globules, which are smaller animalcules, each of which contains within itself a still smaller generation, all perceptible by means of powerful glasses. The lesser globules may be seen escaping from the parent, and increasing in size. Animalcule.

Genus Proteus.—Body very small, simple, transparent, of varying form, changing itself instantaneously into different lobated shapes.

This genus is more obviously contractile than the preceding. It is seldom seen above a minute under the same form, but is continually passing from a simple oval or oblong to an irregular or sinuated shape, and vice versa. A species described by Roësel is so remarkable for this faculty, that it has been compared to a drop of water thrown upon oil. Hence also the generic name.

Sp. 1. *Proteus diffusus.*—Body diverging into branches. Occurs in the water of marshes. Plate XLII. fig. 7, 8, and 9.

Sp. 2. *Proteus tenax.*—Body prolonged to a fine point. Occurs in rivers and in sea-water. There are only two species described as belonging to this genus.

Genus Enchelis.—Body very small, simple, oblong, cylindrical, slightly variable.

There is a marked analogy between this genus and the following. The Enchelides are, however, short and thick compared with the Vibriones, which are slender and lengthened. To the genus now under consideration belong those animals which, if the recorded observations on the subject have been accurately made and faithfully reported, more than any other confound our preconceived ideas regarding the distinction between animal and vegetable life. The species alluded to are named Zoocarps by M. Bory de St Vincent, or animated seeds, which appear reciprocally to give rise to and proceed from certain aquatic plants of the coniferous kind. They are formed in a bulbous-shaped part or swelling of the plant, are ejected when ripe, swim about for some time with a voluntary motion, throw out a root and a branch, become genuine vegetables, produce living seeds, and give birth to animals which, after a similar change of form, speedily return again to the vegetable state. These facts are vouched for by M. Bory de St Vincent, and are credited and confirmed by M. Dutrochet and several other continental inquirers, some of whom declare that they kept so watchful an eye upon the same individual as never to lose sight of it for a moment till they had witnessed the singular transformation above mentioned. We recommend it to our readers' consideration.

Sp. 1. *Enchelis viridis.*—Subcylindrical, obliquely truncated anteriorly. This species has an obtuse tail or terminal part. It continually varies its motion, turning from right to left. Occurs in long-kept water.

Sp. 2. *Enchelis punctifera.*—Subcylindrical, green, obtuse anteriorly, pointed posteriorly. This species is opaque, with a small pellucid spot in the fore part, in which two black points are seen, and a kind of double band crosses the middle of the body. It occurs in marshes. Plate XLII. fig. 10, 11.

Sp. 3. *Enchelis pulvisculus.*—This species bears a great resemblance to the *Monas pulvisculus* of Müller, which is the *E. monadina* of Bory de St Vincent. It is, however, double the size, deeper tinted, and more ovoid. It is found in the waters of marshes, and accumulates around the sides of jars or vases in which coniferous have been kept. It forms on the surface of water a slight pellicle of a delicate green colour, which is supposed to have been erroneously regarded by many botanists as a vegetable production, and described under the name of *Bryssus flos aquae*. On dying it becomes more lengthened and pellucid, or at least retains only a slight central spot of green. Plate XLII. fig. 12.

Sp. 4. *Enchelis amara.*—This is a new species, of a lively green colour, discovered by Bory de St Vincent. In swimming it appears to elongate itself, and advances with the more slender end foremost. Two individuals are sometimes observed to unite and form one animal, of a perfectly spherical form, and similar in aspect to a Volvox.

Sp. 5. *Enchelis tiresias.*—This species was also discovered by the above-named writer, and led to his peculiar views regarding those apparently animated seeds which he has named Zoocarps. He asserts that he has seen this animalcule formed in the articulations of a true conifer; that it burst from its vegetable envelope with a gyration or circular movement; that it soon produced a translucent prolongation of its body, which may be called anterior, as it then swam in the direction of that new organ, which, with the body itself, became visibly longer, till the creature finally acquired the exact form of the *Enchelis deses* of Müller. The chief difference seemed to be that it always moved with the slender end foremost, whereas the species just mentioned swims with its blunt end in advance. It is described by recent French writers as an "animal extraordinaire qui n'est certainement que la graine vivante d'un végétal." (See Dict. Class. d'Hist. Nat. tome vi. p. 156.)

Sp. 6. *Enchelis deses.*—This species is of an obscure green, much enlarged, and moves with the thick end anteriorly. "Celui-ci (the obtuse portion) paraît comme tronqué dans certains aspects; et en examinant attentivement cette sorte de troncature, on la reconnaît formée par un cercle en forme de disque moins foncé que le reste de l'animal. La pointe postérieure est parfaitement hyaline. Dans la pensée où nous sommes que les Enchelides vertes ne sont que des Zoocarpes, ou propagules animés de quelques genres d'Arthrodiées, nous croyons que le disque obscurcié transparent de la partie antérieure n'est que la marque du point sur lequel doit se développer l'article par lequel doit s'allonger en filament conforvoide le Zoocarpe, lorsque, arrivé au terme de sa carrière animale, il doit se fixer et prendre racine par le point hyalin de la partie postérieure." (Loc. cit. p. 157.) We present the above passage to our readers without note or comment, as we do not ourselves understand the zoocarpal nature of an Enchelis.

Genus Vibrio.—Body very small, simple, cylindrical, elongated.

Animalcules have been described as constituents of this genus, which probably do not at all belong to it, being too complicated in their structure. If the *V. aceti*, for example, commonly called the vinegar cel, is furnished with a mouth, lips, and alimentary canal, it does not even pertain to the class Infusoria, however small its dimensions. But many of the species are undoubtedly of the simplest construction; and although they may present some appearance of an internal cavity or sac, they yet exhibit neither mouth nor other external orifice of any kind.

Sp. 1. *Vibrio linola.*—Body linear, extremely minute. Occurs in many vegetable infusions in such numbers as apparently to occupy their entire space. It is so small, that with the best magnifiers little more can be discerned than an obscure tremulous motion. It is supposed to exceed even the *Monas terma* in tenuity. Plate XLII. fig. 13.

Sp. 2. *Vibrio spirillum.*—Filiform, and twisted spirally, which seems to be its natural shape, as it is never observed to unbend, but moves forwards with a vibratory motion at both ends. Found in an infusion of *Sonechus arvensis*. Plate XLII. fig. 14.

Sp. 3. *Vibrio vermiculus.*—Presents a milky aspect, with a blunt apex, and moves with a languid vermicular motion. It has been found in marshy water in November, but is seldom seen. It agrees with the animal mentioned by Leeuwenhoek as occurring in the dung of frogs.

Sp. 4. *Vibrio pazillifer.*—"Animalcule," says Müll-

Animal- "vel congeries animalculorum mirabilia. Pluris in cule. guttulis aquae marinis vidi corpuscula linearia flavescentia (solitariae paleae, in quadrangula disposita scobes referen- tiant), granulaque seminalia qualisque vegetabilis diu credidi; demum nocte inter 6 et 7 Octobrem 1781 as- spectu fili flavescens, sese in longum producentis et in breve contrahentis, ac ex his paxillis compositi, obstupe- factus, novoque phænomeno gavisus, ejusdem variis evo- lutionibus incubui." A salt-water species, abundant in ulva latissima. Observed during the months of September and October. Plate XLII. figs. 15, 16, 17, 18, 19.

Sp. 5. Vibrio serpens.—Slender and gelatinous, with obtuse windings or flexures, resembling a serpentine line. It is rare, and occurs in river-water.

SECTION II.—BODY MEMBRANACEOUS.

Of scarcely perceptible thickness, whether flat or concave.

The organization of the animalcules of this section is scarcely less simple than that of the preceding; but their form, being in a small degree resistant, is less subject to variation from the pressure or other action of the surrounding fluids, which has been regarded as the proof of a certain progress or advance in the scale of structure.

GENUS GONIUM.—Body very small and simple, flattened, short, angular. Some species of this genus appear to be composed of several corpuses united together under a common membrane. This appearance probably results from their cellular tissue, or from certain lines which are the rudiments of those spontaneous divisions formerly mentioned, by which their propagation is affected. Their movements are oscillatory.

Sp. 1. Gonium pectorale.—Quadrangular and pellucid, with sixteen globules of a greenish colour set in a quadrangular membrane, "like jewels in the breast-plate of the high-priest, reflecting light on both sides." Occurs in pure waters. Plate XLII. fig. 20.

Sp. 2. Gonium pulcherrimum.—Quadrangular and opaque. Found in dunghills.

Sp. 3. Gonium corrugatum.—Sub-quadrangular, whitish, marked by a longitudinal line. This species is found in various infusions, particularly that of the pear.

Sp. 4. Gonium truncatum.—Internal molecules dark green. Anterior extremity forming a straight line, with which the sides produce an obtuse angle, terminated posteriorly by a curved line. This species exhibits a languid motion. It is much larger than the preceding, and occurs, though rarely, in pure water.

GENUS CYCLIDIUM.—Body very small and simple, transparent, flattened, orbicular or oval.

The motions of this genus are oscillatory, circulatory, or demi-circulatory, more or less interrupted, and languid or lively, according to the species.

Sp. 1. Cyclidium bulla.—Orbicular and hyaline. General appearance pale and pellucid, with the edges somewhat darker than the rest. It moves slowly in a semicircular direction, and occurs in the infusion of hay.

Sp. 2. Cyclidium hyalinum.—Oval, depressed, perfectly transparent, terminated by a tail-like elongation. This species is very common, and is produced in many infusions, particularly in those of the cerealia. It swims in a vacillating manner, and as if continually trembling. Plate XLII. fig. 21.

Sp. 3. Cyclidium Nucleus.—Of a brownish tinge, deeper behind, and shaped exactly like an apple pipkin.

GENUS PARAMECIUM.—Body very small, simple, transparent, membranous, oblong.

The species of this genus, according to Lamarck, scarcely differ from those of the preceding, except in their more lengthened forms and a slight increase of animal development. They appear to vary instantaneously according to their position in relation to the eye of the observer; but their real form is tolerably determinate. The mode of increasing the species by transverse and longitudinal divisions, or natural cuttings, is very obvious in this genus. They are nearly related to the following, but are less sinuous and irregular. Their movements are for the most part slow and indefinite. They swim horizontally on one of their flattened surfaces, after the manner of flounders.

Sp. 1. Paramaecium aurelia.—Body compressed, with a kind of plait or fold towards the apex, acute behind. Very common in water where confervae grow. Plate XLII. figs. 22, 23, 24.

Sp. 2. Paramaecium chrysalis.—Plicated anteriorly, obtuse behind. Occurs during the autumn in sea-water.

Sp. 3. Paramaecium versutum.—Cylindrical, thickened posteriorly, obtuse at both ends. Found in ditches.

GENUS KOLPODA.—Body very small, simple, flattened, oblong, sinuous, irregular, transparent.

This genus is nearly allied to the preceding, and differs from it chiefly in its more varied forms. It is also less subject to the influence of pressure by the medium in which it lives. An Italian naturalist of the name of Losana has lately published a monograph on Kolpoda; but his figures are somewhat exaggerated, and not very naturally expressed.

Sp. 1. Kolpoda lamella.—Elongated, membranaceous, curved anteriorly. This species is seldom met with. It has a singular vacillatory mode of movement, and advances on its sharp edge, instead of its flattened side, the more usual position.

Sp. 2. Kolpoda gallinula.—Oblong, the anterior portion of the back membranaceous and hyaline. In corrupted sea-water.

Sp. 3. Kolpoda crassa.—Yellow, thickish, somewhat opaque, curved a little in the centre, kidney-shaped. This species has a quick vacillatory motion, and becomes apparent in the infusion of hay generally in about 13 hours. When the water is nearly evaporated it assumes an oval form, becomes compressed, and bursts.

Sp. 4. Kolpoda rostrum.—Oblong, hooked anteriorly. The movements of this species are slow and horizontal. It is found, but not frequently, in water where the lemma grows.

Sp. 5. Kolpoda cucullus.—Ovate, ventricose, the top bent into a kind of beak, and an oblique incision beneath the apex. This species is found in vegetable infusions, and in fetid hay, and usually moves with great velocity. It is pellucid, and appears as if filled with little bright vesicles, which differ in size. Some have supposed them to be lesser animalcules which the Kolpoda has swallowed; but as it has no mouth wherewith to swallow, Müller is more probably right in regarding them in the light of germs. When about to die in consequence of evaporation, it protrudes its contents, whether food or offspring, with great violence. Plate XLIII. figs. 25, 26, 27, 28.

GENUS BURSARIA.—Body simple, membranaceous, concave.

This genus occurs in fresh, saline, and stagnant waters. It appears to vary its form beneath the eye of the observer, and, from a rounded flattened shape, assumes a concave or somewhat purse-shaped aspect.

Sp. 1. Bursaria truncatella.—Follicular, with a truncated apex. This species is visible to the naked eye. It moves from left to right, and from right to left; ascends to the surface in a straight line, and sometimes rolls about as it descends. Sp. 2. *Bursaria bulina.*—Boat-shaped, labiate anteriorly. This species is pellucid and crystalline, with brilliant globules within it. It is concave on the upper side, and convex below.

Sp. 3. *Bursaria hirundella.*—With two small wing-like projections, which give it somewhat of the appearance of a bird. It is invisible to the naked eye, but appears under the microscope like a pellucid hollow membrane. Recent micrographical observers doubt if this species really pertains to the present genus. Plate XLIII. fig. 29.

**Order II.—Appendiculated Infusoria.**

*Furnished exteriorly with projecting parts.*

The animalcules of this second principal order or division, though still infinitely small, gelatinous, and transparent, are so far less simply organized than their predecessors, inasmuch as they are furnished with salient parts, such as hairs, horns, or tail-like appendages, or at least with such projecting organs as, for want of more appropriate terms, we are obliged to designate by those names. They multiply both by division and by the bursting forth of internal germs. Though their essential fluids, and the living tissue which contains them, are probably of a more compound nature than those of the naked Infusoria, they have not yet reached that point of organization in which special organs are developed for the performance of particular functions; and it is not till we reach the higher class of Polypi that these are distinctly perceptible.

"Il paraît," observes Lamarck, "par les nombreuses espèces déjà connues et publiées, que les Infusoires de cet ordre sont bien plus nombreux dans la nature que les Infusoires nus. Cela doit être ainsi d'après les principes que je me suis cru fondé à établir.

"En effet, dans les Infusoires nus, l'origine encore trop récente des races qui proviennent de celles, en petit nombre, qui furent généralement spontanément, n'a pas permis à la durée de la vie et aux circonstances qui ont influé sur ces races, qu'une diversité peu considérable. Mais à mesure que la durée de la vie, que sa transmission dans les individus qui se sont succédés en se multipliant, et que les circonstances ont eu plus de temps pour exercer leurs influences, les races se sont diversifiées de plus en plus, et sont devenues plus nombreuses.

"Cet ordre des choses, qu'il est facile de reconnaître pour celui même de la nature, nous fait sentir pourquoi les Infusoires sont bien moins diversifiées et moins nombreux que les Polypes. Effectivement, quoique nous ne connaissions pas probablement tous les Infusoires, et que nous connaissions bien moins encore tous les Polypes, ce qui est déjà connu de part et d'autre indique que la diversité des Polypes est considérablement plus grande que des Infusoires. Aussi les Polypes sont plus éloignés de leur origine que les Infusoires." (Animaux sans Vertèbres, tome i. p. 433.)

The first genus of this order (*Trichoda*), as constituted by Müller, contains several species which manifest the rudiments of a mouth and the commencement of an alimentary canal: these, according to the negative characters of the class, do not belong to the Infusoria.

**Genus Trichoda.**—Body very small, transparent, diversiform, without caudal appendage, but garnished with soft hairs either on the whole or on part of its surface.

According to the views of Lamarck, this genus contains not only a great proportion of the genus *Trichoda* of Müller, but also the whole of the genus *Leucophora* of the Danish author. It is distinguished from *Kerona* by the want of the long, stiff, distant, corniform hairs which characterize the latter.

A. Body ciliated over its entire surface.

*(Leucophora of Müller.)*

Sp. 1. *Trichoda viridissima.*—Greenish, cylindrical, opaque, thicker posteriorly. Found in sea-water.

Sp. 2. *Trichoda dilata.*—Body flattened, variable, with sinuated margins. Inhabits sea-water, and swims like a Planaria. It scarcely differs from the genus *Kolpoda*, except in being ciliated.

Sp. 3. *Trichoda scintillans.*—Of a green colour, oval, slender, and opaque. Occurs in stagnant water. A doubtful species, closely allied to *Voleox*.

Sp. 4. *Trichoda acuta.*—Ovate, with a sharpened point. Colour yellowish. Of this species the form is very variable. It occurs in sea-water among ulvae. Plate XLIII. fig. 30, 31, 32.

Sp. 5. *Trichoda signata.*—Oblong, sub-depressed, with a blackish margin. Common in sea-water. This species is distinguished by a curved line in its centre, shaped like the letter S, one end of which sometimes assumes a spiral form.

Sp. 6. *Trichoda mammilla.*—Spherical, opaque, with an exsertile papilla. Occurs in the waters of marshes. It is of a dark colour, its short hairs are curved inwards, and it occasionally appears to project and draw in a little white protuberance.

B. Body ciliated, or covered with short hair only over a part of its surface.

*(The greater proportion of the genus Trichoda of Müller.)*

Sp. 7. *Trichoda grandinella.*—Spherical, pellucid, haired above. The minute ciliary appendages of this species are not easily discovered, as it seems to possess the power of withdrawing them at pleasure and instantaneously. It occurs both in pure water and that of infusions.

Sp. 8. *Trichoda cometa.*—Spherical, ciliated anteriorly, with one or more globular appendages behind. Found in pure water in the autumnal season. Plate XLIII. fig. 33, 34.

Sp. 9. *Trichoda solaris.*—Spherical and crystalline, its edges beset with diverging rays, which exceed in length the diameter of the body. This animalcule contracts and dilates, but is stationary in the same spot. In marine infusions. Plate XLIII. fig. 35.

Sp. 10. *Trichoda pules.*—Oval oblong, gibbous, depressed anteriorly. The apex of this species is furnished with hairs, which are seldom visible till it is about to expire, when it protrudes and extends them vehemently, as if in a vain attempt to secure and detain a remaining particle of water.

Sp. 11. *Trichoda proteus.*—Oval, obtuse behind, with an elongated retractile neck. Apex haired. This species, according to Müller and Lamarck, is found in river water. It appears, however, to agree in general character and appearance with the *Proteus* described by Mr Baker, which usually occurs in the slimy matter adhering to the sides of vessels in which either animal or vegetable substances have been some time kept. That of which an account is given by Mr Adams was found in the slime produced by water containing small fishes, snails, &c. The body was something similar to that of a snail, but pointed at one end, while from the other proceeded a long, slender, "and finely proportioned neck, of a size suitable to the rest of the animal." If we credit Mr Baker, this animalcule, though its eyes are not discernible, plainly demonstrates by its actions that it can see; for though multitudes swim about in the same water, and its own progressive motion is very swift, it never strikes against its neighbours, but directs its course with a dexterity "wholly unaccountable should we suppose it destitute of sight." Its entire shape bears a resemblance to that of a swan. See Plate XLIII. fig. 36 and 37. When alarmed, it draws in its supposed neck, becomes more opaque, and moves about slowly with the large end foremost. See fig. 38. After continuing for some time under this form, it will put forth a kind of wheel machinery, the motions of which are alleged to draw a current of water towards it from a considerable distance. After frequently pushing out and pulling in this shorter head, sometimes with and sometimes without the wheel-work, it will remain motionless, as if wearied or worn out; and then its long head and neck or apex will be again slowly protruded, after which it generally resumes its accustomed agility.

Genus Kerona.—Body very small, diversiform, without tail-like prolongation, and furnished with scattered, stiff, corniform hairs on some parts of its body.

To this genus Lamarck has united the Himantopus of Müller. The species are rare. They seldom occur in infusions, and are most frequent in the purer kinds of fresh and salt waters.

Sp. 1. Kerona rostellum.—Orbicular and membranaceous; one side angulated, the other furnished with a series of triple horns. Inhabits sea and river water. This species is alleged by Bory de St Vincent to be entirely destitute of hairs and cirri, and he therefore proposes to remove it to the order Gymnodes, which corresponds with our first order, the naked Infusoria. It is sometimes difficult to identify species in this department, or to ascertain, in a doubtful or contested case, that the same animalcule has been the subject of observation by two or more disputants. Plate XLIII. fig. 39.

Sp. 2. Kerona cypris.—Somewhat pear-shaped, compressed, the front furnished with hairs or vibrating points, inserted beneath the edge, shorter behind, and partly extended straight forward, partly bent downwards. Motion retrograde. Inhabits fresh water.

Sp. 3. Kerona ludia.—Smooth, pellucid, full of small points, the fore part clubbed and a little bent, the hinder part narrow; the base obliquely truncated, and terminating in a tail stretched out transversely. The top of that part which may be called the head, and the centre of the back, are furnished with long hairs. When this animalcule is at rest, its tail is curled; when in motion it is drawn tight and extended upwards. The movements of this species are lively and diverting.

Genus Cercaria.—Body very small, transparent, diversiform, furnished with a distinct but very simple tail.

This genus, as constituted by Müller, contains many species which bear no natural relation to each other; but his characters are precise and definite, and strictly applicable to those species which now form the genus as limited by modern observers. They occur more rarely among animal and vegetable infusions than in running streams and the waters of marshes. Their movements are for the most part circular and very rapid. With the exception of a well-marked tail, their organization is in every other respect extremely simple. If a mouth and the rudiment of a stomach or alimentary canal exist in any of these animals, such characters would remove them not only from the genus Cercaria, but from the class Infusoria, as defined at the commencement of this treatise. A fortiori, the existence of eyes (a fact assumed by some inaccurate observers) in any of the animalcular species, would entirely alter their position and arrangement in the animal kingdom. We cannot do better than report the observations of the venerable Lamarck (himself unfortunately now deprived of sight) on this obscure subject:—"Ici, comme dans le genre suivant, l'on est exposé, d'après la petite extrême des individus, à rapporter à la classe des Infusoires des animaux qui, par leur organisation, appartiennent à d'autres points de l'échelle animale."

"Une bouche, quoique d'abord imperceptible, et conséquemment l'ébauche d'un sac alimentaire, peuvent exister dans certains de ces animaux, et dès lors ils appartiennent au premier ordre des Polypes; mais des yeux, comme on en a supposé dans certains Cercariae, cela est impossible.

"Avant de dire que le fait lui-même vaut mieux que la raisonnement, il faut, 1mo, constater que les points que l'on a pris pour des yeux, en sont réellement, et qu'ils ont chacun un nerf optique qui se rend à une masse médiulaire, centre de rapports pour des sensations; 2do, il faut ensuite établir positivement que des animalcules réellement pourvus d'yeux, sont néanmoins, par leur organisation, de la même classe que les Infusoires." (Animaux sans Vertèbres, tome i. p. 444.)

This genus forms the nucleus of the new family of Infusoria proposed by M. Bory de St Vincent under the name of Cercariées, and which contains in all seven genera, the names and nature of which will be seen by referring to the tabular view. Müller, who was not practically acquainted with the spermatic animalcules, was attracted by the resemblance which some of the Cercaria bore to the figures of those organic molecules in the works of his predecessors. He did not, however, assert their identity; and probably perceived that, although in their general aspect and mode of movement they resembled each other, their peculiar and very different localities, and even the details of their structure, rendered it advisable that they should be assigned to separate genera.

Sp. 1. Cercaria inquieta.—Changeable, convex, with a slender tail. This species occurs in salt water, and is remarkable for assuming a variety of different forms. It is sometimes oval, sometimes cylindrical, sometimes shaped like a sphere. Plate XLIII. fig. 40.

Sp. 2. Cercaria gyrius.—Body of a rounded form, with an acuminate tail. In swimming, this animalcule moves its tail like a tadpole.

Sp. 3. Cercaria lemma.—Changeable, sub-depressed, with an acumulated tail. The C. lemma varies the form of its body in a manner almost as singular as that exhibited by the Proteus, already described. The body is triangular, or oblong, or kidney-shaped. Its tail is at times thick, short, acumulated; at others it is long, cylindrical, and without rings; and when stretched out it sometimes vibrates with such velocity as to appear double. A small pellucid globule, which Müller regarded as the mouth, is perceptible near the apex; and there are also two excessively minute black points, which, whatever they may really be, are by some called eyes. It advances slowly by a few steps or movements at a time, and frequently shakes and bends its tail, in which position it bears a great resemblance to a

---

1 The following are the characters of the genus Zoopera, as recently established: "Corps non contractile, ovoidal, très-comprimé, avec une queue setiforme, aussi longue ou beaucoup plus longue, implantée à la partie postérieure, qui est peu ou point amincie. Ce genre, dont nous possédons un très-grand nombre d'espèces, se compose d'animaux spermatiques." (Dict. Class. d'Hist. Nat. tome iii. p. 356.) The production and existence of these animals, their nature and uses, are still among the many inscrutable mysteries of nature. Jemma leaf in miniature. This animalcule exhibits an advanced organization. Plate XLIII. fig. 41, 42, 43.

Genus Furcocerca.—Body very small, transparent, rarely ciliated, furnished with a bipartite tail.

This terminal genus, according to the views of Lamarck, conducts us to the limits of the infusorial class, and we become thus more liable to deception in regard to the non-existence of a mouth than in the preceding genera. It is a dismemberment of the Ceraria of Müller, and probably contains many species which will be placed elsewhere when future and more continuous observation shall have thrown additional light upon their nature and attributes.

Sp. 1. Furcocerca podura.—Cylindrical, acuminated posteriorly. This species is pelucid, and seems to consist of a head, trunk, and tail, the first of which, in the view of some observers, “resembles that of a herring.” It turns round as if upon an axis when it moves, and is usually found in the months of November and December, in places where the lemma abounds. The tail frequently, but not always, appears to be divided into two. One of Müller’s figures of this species is probably erroneous. He represents it as covered with short hairs; whereas, to more recent observers, it appears perfectly smooth. Plate XLIII. fig. 44, 45.

Sp. 2. Furcocerca viridis.—Cylindrical, variable, divided and acuminated behind. Occurs in spring in ditches and standing pools. It frequently contracts its anterior and posterior portions, so as to assume a spherical form. It is difficult to determine the genus to which this species belongs. Lamarck is supposed to have erred in placing it where it now stands. In truth, the genus appears to have been rather established provisionally, than upon an assured and natural foundation. The varying forms of the species which it contains render it extremely difficult either to discern or describe them with precision. Plate XLIII. fig. 46, 47, 48.

We have now endeavoured to present a general view, and a systematic exposition, of the principal features of the animalcular world; and if our statements have been less explicit, and our arrangement less complete and methodical, than accords with the reader’s expectation, these defects must in part be attributed to the uncertainty which still prevails regarding a subject of which many of the essential characters scarcely lie within the limits of human intelligence. The observations and experiments of the English microscopical observers of last century, though they might amuse the general student, are too vague and fanciful to be now regarded as parts of the assured history of animalcules. The ultra-analogical reasoning on subjects of natural science with which we have been lately favoured by such men as Oken and Geoffroy St Hilaire, are tame in comparison with the inferences deduced by some of our older observers, who describe with minuteness the head, eyes, mouth, jaws, throat, stomach, intestines, and other parts of animalcules, which the improved glasses of modern times do not reveal to the vision of not less patient inquirers. The recent observations on the motions of the pollen of plants, which have puzzled the modern philosophers, would have opposed but feeble barriers in the way of our predecessors. “To discover,” says Buffon, “whether all the parts of animals, and all the seeds of plants, contained moving organic particles, I made infusions of the flesh of different animals, and of the seeds of more than twenty different species of vegetables; and after remaining some days in close glasses, I had the pleasure of seeing organic moving particles in all of them. In some they appeared sooner, in others later; some preserved their motions for months, and others soon lost it. Some at first produced large moving globules resembling animals, which changed their figure, split, and became gradually smaller; others produced only small globules, whose motions were extremely rapid; and others produced filaments, which grew longer, seemed to vegetate, and then swelled and poured forth torrents of moving globules.” It was from these and similar observations that the theory arose proposed by Baron Munchausen (an ominous name!). The Baron perceiving that these moving globules, after taking a little exercise, began again to vegetate, drew the conclusion that they were first animals and then plants; thus anticipating by more than half a century the supposed discoveries of some modern physiologists. Which of them was first in error it is perhaps of little consequence to inquire; and we allude to the subject here rather in connection with some singular observations by Mr Ellis, recorded in the 59th volume of the Philosophical Transactions, than from its own intrinsic importance. His object was to overturn Munchausen’s hypothesis, by showing that the supposed Zoocarpes were nothing more than “the seeds of that genus of fungi called mucor or mouldiness,” and that their motions were caused by the attacks of myriads of animalcules! “Having at the request of Dr Linnæus made several experiments on the infusion of mushrooms in water, in order to prove the theory of Baron Munchausen, that these seeds are first animals and then plants, it appeared evidently that the seeds were put in motion by very minute animalcules, which proceeded from the putrefaction of the mushroom: for by pecking at these seeds, which are reddish, light, round bodies, they moved them about with great agility in a variety of directions; while the little animals themselves were scarcely visible till the food they had eaten had discovered them. The satisfaction I received from clearing up this point led me into many other curious and interesting experiments. The ingenious Mr Needham supposes these little transparent ramified filaments, and jointed or coralloid bodies, which the microscope discovers to us on the surface of most animal and vegetable infusions when they become putrid, to be zoophytes, or branched animals; but to me they appear, after a careful scrutiny with the best glasses, to be of that genus of fungi called mucor or mouldiness, many of which Michellius has figured, and Linnæus has accurately described. Their vegetation is so amazingly quick, that they may be perceived in the microscope even to grow and feed under the eye of the observer. Mr Needham has pointed out to us a species that is very remarkable for its parts of fructification (See Phil. Trans. vol. xlv. tab. 5, fig. 3, a, A). This, he says, proceeds from an infusion of bruised wheat. I have seen the same species proceed from the body of a dead fly, which was become putrid by lying floating for some time in a glass of water where some flowers had been, in the month of August 1768. This species of mucor sends forth a mass of transparent filamentous roots; from whence arise hollow stems, that support little oblong oval seed-vessels, with a hole on the top of each. From these I could plainly see minute globular seeds issue forth in great abundance, with an elastic force, and turn about in the water as if they were animated. Continuing to view them with some attention, I could just discover that the putrid water which surrounded them was full of the minutest animalcule; and that these little creatures began to attack the seeds of the mucor for food, as I have observed before in the experiment on the seeds of the larger kind of fungi or mushrooms. This new motion continued the appearance of their being alive for some time longer; but soon after many of them arose to the surface of the water, remaining there without motion; and a succession of them afterwards coming up, they united together in little thin masses, and floated to the edge of the water, remaining there quite inactive during the time of observation." In like manner, the movements of the jointed coraloid bodies which Mr Needham has named chaplets and pearl necklaces are attributed to the attacks of their animalcular enemies. "When a small portion of these branches and seeds are put into a drop of the same putrid water upon which the scum floats, many of these millions of little animalcules with which it abounds immediately seize them as food, and turn them about with a variety of motions, as in the experiments on the seeds of the common mushrooms, either singly, or two or three seeds connected together; answering exactly to Mr Needham's description, but evidently without any motion of their own, and consequently not animated!"

We shall conclude this subject with a short notice of another view of the matter, which has resulted from some recent experiments and observations by our celebrated botanist Robert Brown. While engaged in some inquiries regarding the structure of the pollen of plants, and its mode of action on the pistillum of phanerogamous tribes, that accurate observer had occasion to immerse in water some particles taken from the full-grown anthers (previous to bursting) of Clarkia pulchella. Of these, he perceived by the microscope that many were evidently in motion, and that their motion consisted not only of a change of place in the fluid, but of a change of form in themselves; that is to say, a contraction or curvature about the middle of one side, accompanied by a corresponding enlargement or convexity on the other, frequently occurred. The particles were seen, in a few instances, to turn on their longer axis; and their general motions were of such a nature as to produce the conviction in Mr Brown's mind that they did not arise either from currents or evaporation of the fluid, but were proper to the particles themselves. Having ascertained that motion existed in the pollen of all the living plants which he examined, he next inquired whether, and for what length of time, this singular property was retained after the death of the plant. Specimens were experimented on, which had been dried and preserved in an herbarium for 100 years, and the moving molecules or small spherical bodies were still perceived in considerable numbers.

"The very unexpected fact," says Mr Brown, "of seeming vitality retained by those minute particles so long after the death of the plant, would not perhaps have materially lessened my confidence in the supposed peculiarity; but I at the same time observed, that on bruising the ovula or seeds of Equisetum, which at first happened accidentally, I so greatly increased the number of moving particles, that the source of the added quantity could not be doubted. I found also, on bruising first the floral leaves of mosses, and then all other parts of those plants, that I readily obtained similar particles, not in equal quantity indeed, but equally in motion. My supposed test of the male organ was therefore necessarily abandoned. Reflecting on all the facts with which I had now become acquainted, I was disposed to believe that the minute spherical particles or molecules of apparently uniform size, first seen in the advanced state of the pollen of Onagrarix, and most other phanerogamous plants,—then in the antheric of mosses, and on the surfaces of the bodies regarded as the stamens of Equisetum,—and, lastly, in bruised portions of other parts of the same plants,—were in reality the supposed constituent or elementary molecules of organic bodies, first so considered by Buffon and Needham, then by Wrisberg with greater precision, soon after and still more particularly by Müller, and very recently by Dr Milne Edwards, who has revived the doctrine, and supported it with much interesting detail. I now, therefore, expected to find these molecules in all organic bodies; and accordingly, on examining the various animal and vegetable tissues, whether living or dead, they were always found to exist; and merely by bruising these substances in water, I never failed to disengage the molecules in sufficient numbers to ascertain their apparent identity in size, form, and motion, with the smaller particles of the grains of the pollen. I examined also various products of organic bodies, particularly the gum raisins, and substances of vegetable origin, extending my inquiry even to pit-coal; and in all these bodies molecules were found in abundance. I remark here also, partly as a caution to those who may hereafter engage in the same inquiry, that the dust or soot deposited on all bodies in such quantity, especially in London, is entirely composed of these molecules. One of the substances examined was a specimen of fossil wood, found in Wiltshire oolite, in a state to burn with flame; and as I found these molecules abundantly and in motion in this specimen, I supposed that their existence, though in smaller quantity, might be ascertained in mineralized vegetable remains. With this view, a minute portion of silicified wood, which exhibited the structure of conifers, was bruised, and spherical particles, or molecules in all respects like those so frequently mentioned, were readily obtained from it; in such quantity, however, that the whole substance of the petrifaction seemed to be formed of them. But hence I inferred that these molecules were not limited to organic bodies, nor even to their products. To establish the correctness of the inference, and to ascertain to what extent the molecules existed in mineral bodies, became the next object of inquiry. The first substance examined was a minute fragment of window-glass, from which, when merely bruised on the stage of the microscope, I readily and copiously obtained molecules, agreeing in size, form, and motion, with those which I had already seen. I then proceeded to examine, and with similar results, such minerals as I either had at hand or could readily obtain, including several of the simple earths and metals, with many of their combinations. Rocks of all ages, including those in which organic remains have never been found, yielded the molecules in abundance. Their existence was ascertained in each of the constituent minerals of granite, a fragment of the sphinx being one of the specimens examined. To mention all the mineral substances in which I have found these molecules would be tedious; and I shall confine myself, in this summary, to an enumeration of a few of the most remarkable. These were both of aqueous and igneous origin, as travertine, stalactites, lava, obsidian, pumice, volcanic ashes, and meteorites from various localities. Of metals I may mention manganese, nickel, plumbago, bismuth, antimony, and arsenic. In a word, in every mineral which I could reduce to powder sufficiently fine to be temporarily suspended in water, I found these molecules more or less copiously; and in some cases, more particularly in siliceous crystals, the whole body submitted to examination appeared to be composed of them."

There were three points of importance which Mr Brown was anxious to ascertain regarding these molecules, viz. their form, whether they were of uniform size, and their absolute magnitude. He seems, however, not to have been entirely satisfied with his determination on any of these points. As to form, he states the molecules to be spherical. His manner of estimating the absolute magnitude and uniformity of size of the molecules found in the various bodies submitted to examination, was by placing them on a micrometer divided to five thousandths of an inch, the lines of which were very distinct; or, more rare- Animalcule, on one divided to ten-thousandths, with fainter lines, not readily visible without the application of plumbago, as employed by Dr Wollaston, but which in this case was inadmissible. The results can only be regarded as approximate, but Mr Brown is disposed to believe that the molecule is of uniform size, though, as existing in various substances, and examined in circumstances more or less favourable, he regards it necessary to state that its diameter appeared to vary from \( \frac{1}{5000} \)th to \( \frac{1}{2000} \)th of an inch.

**Supplementary Observations.—1853.**

Since the preceding exposition of animalcules was written, great and important additions have been made to our knowledge of the subject. Both the organic structure and the physiological functions of these creatures have been described at great length, and amply illustrated, by Ehrenberg of Berlin. We are deeply indebted to that author for much that he has achieved in an obscure and difficult department,—for his general views, not less than his detailed descriptions,—and especially for the influence which he has shown many animalcular beings to have exercised, by means of their siliceous remains, in the building up, as it were, of various geological formations. At the same time it must be borne in mind, that many of Ehrenberg's discoveries have been much contested, and that Dujardin and other recent writers do not accept his classification, in consequence of what they deem its hypothetical basis. In presenting the views of the first-named observer, we therefore do so under a sense of the critical correction which others have sought to bestow upon them, and of which we shall also in our present supplement endeavour to give a brief account.

The following is a summary of Ehrenberg's views of the general character and attributes of infusorial beings.

They are all organized,—the greater portion (probably all of them) highly organized bodies.

They constitute two very natural classes (Polygastrica and Rotatoria), according to their structure, and are further subdivisible upon the same principle.

Their existence in all quarters of the earth and sea, is proved; as is also that of individuals of the same species in the most opposite ends of the world.

Their geographical distribution upon the earth follows the laws observed as regulating that of other natural bodies.

Most of the Infusoria are invisible to the naked eye; many are just visible as moving points; the size of the body does not in any case exceed \( \frac{1}{4} \)th of an inch.

Invisible Infusoria, in consequence of their vastly aggregated numbers, colour large tracts of water with remarkable hues.

Though themselves invisible, they also give rise, in consequence of this aggregation, to a certain kind of marine phosphorescence.

They sometimes compose, though singly invisible, a kind of mould, very obvious in consequence of the multitudinous mass. In a single cubic inch of this mould, there may be above 41,000 millions of animalcules; and they probably constitute the chief proportion of living bodies on the face of the earth.

They are the most reproductive of all organized beings; and from one of their known modes of propagation, that of self-division, ensues a continual destruction of the individual, and yet a similar interminable preservation and extension of it, in air and water, bordering, it may be almost said, upon eternal life and growth.

The copulation of gemmae, which perhaps includes the hitherto unsolved poly-embryonate riddle of the seeds of all plants and vegetable formations, is solved in the animalcular family of Closterina.

They form in the course of time, in consequence of the enduring nature of their siliceous shells, indestructible earths, stones, and rocky masses.

With lime and soda we can prepare glass and swimming bricks out of invisible animalcules; we can use them as flints, and probably prepare iron from them; we use mountain meal, which is composed of them, as food in hunger.

They are sometimes injurious, by causing the death of fish in ponds, deteriorating clear water, and causing boggy smells; but they do not, as some have supposed, give rise to malaria, plague, and other maladies.

They appear to be, as far as yet known, sleepless.

They partially break up in reproduction (egg-laying), and thereby passively undergo great alterations of form.

They form invisible intestinal beings in man and other animals, even if the Spermatooza are excluded from among them. They are themselves infected by both external and internal parasites.

---

1. The following summary from the pen of Mr Brown contains the renewed expression of that gentleman's opinion, matured by some recent experiments on the subject of active molecules. "That extremely minute particles of solid matter, whether obtained from organic or inorganic substances, when suspended in pure water or in some other aqueous fluids, exhibit motions for which I am unable to account, and which, from their irregularity and seeming independence, resemble in a remarkable degree the less rapid motions of some of the simplest animalcules of infusions. That the smallest moving particles observed, and which I have termed Active Molecules, appear to be spherical, or nearly so, and to be between \( \frac{1}{6000} \)th and \( \frac{1}{3000} \)th of an inch in diameter; and that other particles of considerably greater and various size, and either of similar or of very different figure, also present analogous motions in like circumstances. I have formerly stated my belief that these motions of the particles neither arose from currents in the fluid containing them, nor depended on that intestine motion which may be supposed to accompany its evaporation. These causes of motion, however, either singly or combined with others,—as the attractions and repulsions among the particles themselves, their unstable equilibrium in the fluid in which they are suspended, their hygrometrical or capillary action, and in some cases the disengagement of air bubbles, or of minute air-bubbles,—have been considered by several writers as sufficiently accounting for the appearance. Some of the alleged causes, as I stated, with others which I have considered it unnecessary to mention, are not likely to be overlooked, or to deceive observers of any experience in microscopic researches; and the insufficiency of those enumerated may, I think, be satisfactorily shown by means of a simple experiment. This experiment consists in reducing the drop of water containing the particles to microscopic minuteness, and prolonging its existence by immersing it in a transparent fluid of inferior specific gravity, with which it is not miscible, and in which evaporation cannot take place. If, to almond oil, which is a fluid having these properties, a considerably smaller proportion of water, duly impregnated with particles, be added, and the two fluids shaken or triturated together, drops of water of various sizes, from \( \frac{1}{6000} \)th to \( \frac{1}{3000} \)th of an inch in diameter, will be immediately produced. Of these, the most minute necessarily contain but few particles, and some may be occasionally observed with the particle only. In this manner minute drops, which, if exposed to the air, would be dissipated in less than a minute, may be retained for more than an hour. But in all the drops thus formed and protected, the motion of the particles takes place with undiminished activity, while the principal causes assigned for that motion, namely, evaporation and their mutual attraction and repulsion, are either materially reduced or absolutely null."

2. Among other difficulties with which the student of this department will have to contend is the following,—that many species classified by Ehrenberg and others as animalcules, are considered by botanists as pertaining to their particular kingdom. Thus the Desmidaceae, a great constituent group of Ehrenberg's family Basillaria, are viewed by Professor Bailey of New York as belonging to the vegetable kingdom. Among ourselves, Dr Harvey is noted for his knowledge of marine plants, classes both these and the Diatomaceae, as sub-orders of the Chlorophyceae, or green Algae. Mr Ralfs, who has written so excellent a monograph on the "British Desmidiae," likewise regards these as Algae. It is indeed a vexed question as to the animal nature even of the Diatomaceae, which, by means of genera such as Melosira, and others, seem closely connected with the confervoid Algae. They possess comparatively a lengthened life.

As the pollen of pine trees falls yearly in the form of sulphur-rain, so do the much more minute animalcules appear (being elevated by means of watery vapour) floating alive in the atmosphere, and sometimes even mixed with dust.

They generally, like the more highly-organized bodies, maintain themselves pretty uniformly against all external influences. Although they sometimes consume strong poisons without immediate injury, they do not do so without an after effect.

The weight of invisible Infusoria, although light, is calculable, and the most gentle current of air or draught can play with their bodies as with the vapour of water.

The obvious and very rapid motion of Infusoria, is reducible as follows:—Hydatina senta moves 1-12th of an inch in 4 seconds; Monas punctum, the same in 48 seconds; while Nucicola gracilis takes 6 minutes 24 seconds to go the same distance.

Linnaeus said, omnis calx e vermis: either to maintain or deny omnis silex omne ferrum vermis would now be unjust.

Direct observations on the theory of generation primativa are wanting in necessary strictness. Those who profess to have seen the sudden origin of the minutest Infusoria from elementary substances, have quite overlooked the compound structure of these organic bodies.

The frequent and wonderful changes of form of many Infusoria no doubt have their limits, although the laws which govern them are still to be defined.

The power of infusorial organization is exhibited by the strong chewing apparatus, with teeth, which they possess, and their exhibition, also, of a complete mental activity.

The study of the Infusoria has led to a more distinct and conclusive notion of animal organization in general, and of the limits which circumscribe the animal form; from which all plants and minerals, which want the animal organic system, are strongly and distinctly separated.

It finally results from these inquiries, that experience shows an unfathomableness of organic creations, when attention is devoted to the smallest space, as it does of stars when directed to distances the most immense.

It was the prevailing opinion, till of later years, that the generality of animalcules were devoid of external organs; but the use of coloured substances, and the introduction of achromatic glasses have certainly shown a much more composite structure than was formerly known to exist. The simplest member is a delicate filament, placed near the oral orifice, and therefore called the proboscis. When the animalcule is in motion, this proboscis seems to act as a sort of ear or paddle, while, at the same time, by creating a current in the direction of the mouth, it aids in the prehension of food. Cilia are shortish hairs, placed apparently upon a bulb. They vibrate rapidly, the hair turning round upon something like an articulated surface, while the points describe a comparatively large circle. These cilia show themselves remarkably among the Rotatoria, in the shape of wheels, and both in form and action may be regarded as among the most interesting spectacles presented by the animalcular world. Naturalists are somewhat divided regarding their functions. Many look upon them as organs of respiration, and there is no doubt that corresponding parts are placed around the gills of many mollusca, and bring to them currents of fresh water for the purposes of breathing. Of the existence of eyes in the animalcular world we are still extremely doubtful, when we consider the fact of their non-existence in great groups distinguished in all other respects by a more complex and complicated organization. In Müller's great work no eyes are represented in any of the Polygastric species, but certain specks containing a red pigment have been assumed as eyes by Ehrenberg; and he argues that even if no other proof of the existence of a nervous system in these animated atoms could be adduced, the visual spots referred to would be sufficient to prove it. Having, as he supposes, discovered visual organs in these red specks of the Rotatorial families, he argues from analogy that the same parts perform similar functions in the Polygastric groups. M. Valenciennes maintains that in the Rotatoria these eye-specks are distinctly defined, have an investing capsule, and a crystalline lens, and consequently possess the essential attributes of organs of sight. On the other hand, owing to the extreme minuteness of the Polygastric species, all appearance of definite outline is wanting in their red specks, and as similar characters occur upon the reproductive germs of Algae (which belong to the vegetable kingdom), their necessarily visual character is denied by many considerate observers.

"The sense of sight," says M. Dujardin, "would partake more of the character of a reality if the colour of a speck without appreciable organization, without a constant form, or a precise contour, sufficed to prove the existence of an eye. But in the genus Euglena, which is particularly cited as characterized by such an organ, the red spot so regarded is excessively variable, sometimes multiple, at other times made up of irregularly aggregated granules. Analogy, too, is inadequate to the solution of the question; for, on descending the animal series, to determine the nature of this coloured speck, we have to leap from the Daphniae (an Entomostracal tribe) with a moveable eye, repeating in its composition that of Insects and Crustacea, to animals presenting nothing but diffused coloured specks.

"Such spots, whether in number or position, have so little physiological importance in the Planariae, and in certain Annélides, that they are often not even to be employed as an absolute specific character. In the Rotatoria, the analogy with which is more especially insisted on, these pigment spots are, in some species, known to disappear from age, and in others to become more evident in proportion to size or development of individuals: so that the learned micrographer of Berlin, in his attempt to base the generic characters of these animals on the presence and number of eyes, has been led to place in different genera, species very closely allied, if not identical. Indeed, that a black or a red colour is in general an attribute of the pigment of eyes, cannot be a reason for concluding an eye to exist wherever we find such colours; if so, we must accord it to some intestinal worms, such as the Scolex polymorphus, which has two red spots on the neck, to the Actinia, which are often strewed with such specks, and also to some bivalved mollusks.

"If the ability of the Infusoria to direct their course through the liquid, and to pursue their prey, be appealed to in evidence, it is certainly, in the first place, necessary to verify the reality of this faculty, which I think equally fabulous with all related concerning the instincts of these animals. Indeed it would not even prove the red specks to be eyes, since the greatest number of Infusoria supposed to be endowed with such a faculty are in want of them; and those which do possess them do not exhibit that power in any higher degree of development."

In the opinion of M. Morren, the red pigment specks of Lagenella, Cryptoglena, and Trachelomonas, cannot be eyes, because in the last-named genus the coloured pigment is capable of being distributed over the whole body, in which case, according to Ehrenberg's supposition, the creature itself would be converted into nothing but an eye.

Professor Owen observes, in relation to the movements of Polygastric animalcules, that although they may be per-

---

1 Histoire des Infusoires. 2 Mem. de l'Acad. de Bruxelles, 1841, taf. 14. ceived to avoid obstacles in their way, and rarely jostle one another, it is yet difficult to detect any definite cause or object of their movements. After carefully watching for signs of volition, that great observer came to the conclusion that those movements partook in general of the nature of respiratory acts, rather than of attempts to obtain food or avoid danger. They seemed automatic rather than voluntary, as if governed by stimuli within or without the body, not felt, but reflected upon contractile fibre, and are therefore motions which never tire. He thus explains the fact already indicated in our abstract of Ehrenberg's general views, namely, that at whatever period of the night we examine living Infusoria, we shall invariably find them as ceaselessly active as during the meridian splendour, and thus that animalcules never sleep.

The same unsettled state of opinion as regards the eyes, pervades our knowledge of other important parts of animalcular economy, and even the great basis (the assumed peculiarities of the digestive system) of Ehrenberg's classification being regarded as hypothetical, the classification itself has been by many rejected on that ground. According to the Berlin naturalist, the functions of digestion among the Polygastrica are effected by means of numerous internal vesicles or stomachs; while in the Rotatoria, as in the generality of higher animals, there is only one. While studying species of the former class, Ehrenberg observed a vesicle to fill with food, and then saw the particles pass into another cell, and so on until, the nutritive portions having been imbibed by each stomach in succession, the refuse was discharged by the animalcule. That many other naturalists have been unable to detect this process is perhaps no conclusive argument against it, as great experience, and the most steadfast and accurate observation, are necessary in microscopical pursuits. Few have been able to detect the tubular connection between these stomachic cells, which, however, must exist if Ehrenberg's views are well founded. He affirms that he has often seen it, and the passage is very distinctly shown upon his plates. Baron Gleichen regarded these vesicles as eggs, although he failed to witness their discharge; and the existence of eggs among the Polygastric tribes, is perhaps as much of an assumption as any other. So far back as 1781, he tried to make certain Infusoria eat carmine, and found on the ensuing day that several of them had red granules in their interior. He concluded that they had swallowed the colouring matter, and more recent repetitions of similar experiments led to the formation of Ehrenberg's system. Professor F. T. Meyen refuses to admit the facts on which it is founded, not only because he has failed to see the intestinal communication between the stomachs, but has observed these supposed stomachs moving rapidly in the interior of the body of many species, after the manner of those granules which circulate in the joints of Chara. He has often seen Vorticella with many globules of indigo in their interior, always moving round a centre; from which he infers there could not be a communicating canal between the so-called stomachs with an oral orifice, and an extremity directed towards the mouth. In regard to the true nature of these vesicles, and balls of similar diameter, found in the bodies of Infusoria, Meyen is of opinion that the true Infusoria are themselves vesicular beings, the interior of which is filled with a mucous substance: the thickness of the membrane forming the vesicle is easily ascertainable in several species, and in many he has noticed in this membrane an obvious spiral structure, resembling that which exists among cellular vegetables. In the larger Infusoria, a cylindrical canal (the oesophagus) traverses obliquely the membrane which forms the animal. The lower extremity of this canal dilates, more or less, when the creature has taken food, until it attains the dimensions of the balls, which are so obvious in the interior of these Infusoria. The inner surface of this upper portion of the intestinal canal is provided with cilia, which turn round not only alimentary substances but foreign bodies, till they have assumed a spherical form. During the formation of this ball, the stomach, according to Meyen (who admits that the part in question must be distinguished by that name), has a free communication with the oesophagus; and by means of the ciliary apparatus found at its exterior, new alimentary substances are introduced into this canal, and pushed as far as the stomach. When the ball has acquired the dimensions of the stomach, it is expelled by its inner extremity, and pushed into the cavity of the body. It there forms an additional ball, if any solid substances had previously existed in the surrounding liquid. This second ball is itself pushed into the interior of the cavity of the animal, and drives before it the first ball along with the mucosities between the two—a successive formation of similar balls, by the food or other matter received into the animal, going on without interruption. Now, Meyen maintains that it is the simultaneous existence of many of these balls which has caused Ehrenberg to believe that these animalcules were Polygastric. To follow their formation, our observations must commence at the moment the animalcules are plunged into coloured liquid. The swallowing of the coloured particles takes place with great rapidity, frequently in half a minute, and the coloured balls may be seen one after another issuing from the stomach, and proceeding downwards along the internal wall of the cavity of the body. Their number is often so considerable as to fill the entire cavity, and they lie so close together as to form a large mass, which, as in the genus Vorticella, slowly turns upon itself. The vesicular cavities, according to Meyen, are not stomachs, and possess nothing in common with the balls, although the latter may get into them singly, but at the same time accidentally. The formation of these cavities, as well as their sudden and entire disappearance, may be traced as easily as the origin of the balls. It is even possible sometimes to see how one of these cavities moulds itself over a ball, and then disappears. The microscope reveals to us that they are not lined with a particular membrane, but are simply excavations of the pulpy substance. They often show themselves close to the inner surface of what forms the skin of the creature, and sometimes increase so greatly, that the diameter of even one is equal to the third or one-half of the entire cavity of the body.

---

1 Comparative Anatomy and Physiology of the Invertebrated Animals, p. 19. 2 As the use of infusions is indispensable in the study of living microscopic objects, we extract the following notice of the method of feeding infusions with coloured substances, from Mr Pritchard's work. Select for the purpose such coloured substances as are entirely free from metallic acids, and not chemically soluble in water. They must, however, be capable of a very minute mechanical division. The substances generally used are carmine, indigo, and sap-green, the first being preferable. The material should be as pure as possible. Rub a piece of it once or twice on the stage glass, or what is better, the lower plate of an aquatic air-box, having first moistened it with a drop of water. The quantity of coloured matter is very small, no more than sufficient to render it appreciable by the naked eye; for if there be too much, the chances are that the particles will be too large for the creatures to imbibe. Having thus prepared the coloured food, place a drop of it beside a drop of water containing the animalcules, but not so near as that they may come in contact; then put gently on the cover of the air-box, and lower it sufficiently to flatten the two drops of fluid, but not to force them to unite. Now place the air-box under the microscope, and examine the animalcules closely, so as to ascertain that their stomachs are colourless; then press down the cover until the drops of fluid intermingle, which may be done under the microscope, and you will immediately perceive the creatures in great activity, and readily distinguish the cilia and proboscis of such as possess those parts, while in a few seconds their stomachs will be filled by the coloured substance.—See Infusorial Animalcules, p. 108. 2d Ed. 1852.

3 Edin. Phil. Jour., vol. xxviii. According to Dujardin, the Infusoria (setting aside the Systolides or Rotatoria, as much higher in the animal scale, and also the Bacillaria, which, with Clasteria, are more nearly related to the vegetable kingdom) derive their origin for the most part from obscure or unknown germs, in artificial and natural infusions, stagnant water, and rivers, or such portions of them as rest over vegetable remains; no other mode of propagation, except self-division, being well ascertained. Their fleshy substance is dilatable and contractile, like the muscular flesh of the higher animals, but it exhibits no absolute trace of fibres or membrane, seeming, on the contrary, to be homogeneous and diaphanous, except in cases where the surface appears articulated from contraction. This fleshy matter when isolated by tearing, or the death of the animalcule, shows itself in the liquid in the form of lenticular discs or globules, which refract light but slightly, and are capable of producing spontaneously in their substance spherical cavities analogous in appearance to the vesicles of the interior. In the living creature some of these vesicles are produced at the base of a sort of mouth, and are destined to contain the water swallowed with the aliment. They then pursue a certain course in the interior, and contract, and leave nothing in the centre of the fleshy substance, except the undigested particles. They can even discharge their contents externally by a fortuitous opening, which may be reproduced several times towards the same, though not the identical, point. The vesicles containing the aliment are independent, and neither communicate with an intestine, nor with each other, except in those cases where two vesicles incorporate. The other vesicles, which contain nothing but water, are formed much nearer the surface, and seem capable both to receive and expel their contents through the meshes of the integument. Spallanzani considered them as respiratory organs, and they may be so regarded, at least in so far as they multiply the points of contact of the interior substance with the circumambient fluid.

Dujardin is, moreover, of opinion in regard to the so-called eggs of Infusoria, their generative system, their organs of sense, their nerves and vessels, that none of these can be ascertained or determined with exactitude; and everything inclines him to believe that these minute creatures, although clearly endowed with a simple organization, according with their mode of life, cannot be regarded as possessing the same systems of organs as the higher tribes. The coloured points, for example, usually of a red colour, which have been regarded as eyes, cannot with propriety receive that appellation.

Siebold is also opposed to the view that these vesicles or sacs are special and distinct digestive organs, and he denies the existence of any connecting canal. The Astoma (mouthless animalcules) he regards as nourished only by a general absorption of the surface. In the Stomatoda (those with evident mouths) he represents the oral orifice as continued into the interior by a sort of oesophagus, wide, and of very various form, terminating abruptly in the general loose parenchyma of the body. The food, when sought for, is drawn towards the mouth by the action of the surrounding cilia, and having been received into the mouth, enters the oesophagus, and is thence pushed onwards by a contraction of the part, in the form of a rounded globe, into the interior. After performing, during a sojourn there, a greater or less circuit, the food in the generality of Stomatoda is ejected through a fixed outlet, not, as Dujardin maintains, by means of a varying opening through the surface.

Wagner asserts that no one by any examination, however close, can convince himself of the actual existence of such an organization as Ehrenberg affirms. He maintains that in many Infusoria, where comparatively large bodies, such as Navicula or joints of Alga, have been swallowed, no surrounding vesicle can be seen, and that these bodies will sometimes occupy the entire length and breadth of an animalcule. In the absence of mouth, nutrition seems carried on by the general surface. It may be safely inferred from these conflicting opinions that no settled or satisfactory conclusion can be formed, and that Ehrenberg's theory of polygastric structure, though it may be true, requires confirmation. The same may be said of several other organs and their functions. We have dwelt upon the digestive system at greater length than we shall do upon any other, as it forms the basis of Ehrenberg's arrangement of the animalcular kingdom.

In regard to the reproductive process among these infusorial tribes, Monas vivipara is regarded by Ehrenberg as the only species of the class that is viviparous. The formation of eggs, is considered by that author as a fertile and frequent source of increase. Dujardin, again, views the viviparous attributes of the above-named Monas as more than doubtful, and the formation of ova in any infusorial species as by no means ascertained. He considers Ehrenberg's instances of oviposition as examples merely of diffusion, or the breaking up of the gelatinous substance of the animalcule into spherical atoms from want of moisture. With Siebold, he limits the reproductive process in this class to the two forms of gemmation and spontaneous fission. If this be true, then all that has been written of the ovaries, vesiculae seminales, &c., falls to the ground. Professor Owen, however, is of opinion that the function of the nucleus of Infusoria in reproduction by spontaneous fission may be regarded as analogous to that of the essential contact of the Spermatozoon with the germ-cell in the development of the higher classes; and comparing the results in the two cases, he says it is certain "that the analogy between these phenomena in the multiplication of the parts of the germ-mass and those of the nucleus in the multiplication of monads is so close, that one cannot reasonably suppose that the nature and properties of the nucleus of the impregnated germ-cell, and that of the monad can be different." He therefore infers that the nucleus of the Polygastric animalcules is the seat of the spermatic power, though the term testes can only be figuratively applied; and he thinks that if Ehrenberg be correct in viewing the interstitial corpuscles as germ-cells, these essential parts of ova may receive the essential matter of the sperm from the nucleus, which is discharged along with them in the breaking up of the monad, which Ehrenberg regards as equivalent to an act of oviposition; and impregnated cells may thus, in Professor Owen's view, be prepared to diffuse through space, and carry the species of Polygastric animalcules to a distance from the scene of the life of the parent.

Professor Weisse supposes himself to have detected reproduction by ova in Chlorogonium euchlorum, and maintains that the continuous observation of that species demonstrates that several of Ehrenberg's genera are nothing more than its natural development from stage to stage. He describes the green matter of chlorogonium as developing, by spontaneous fission of itself, numerous young animalcules, which at first resemble Uvella Bodo, and are afterwards converted into Chlorogonium euchlorum and Glenomorium tingens. What he calls oviposition is the escape of the young by a transverse rupture of the parent, which is itself sacrificed, and disappears as a shrivelled sack. But in conformity with Thuret's views, it may be doubted whether the organic being (we shall not say creature) were really an animalcule, and not merely a thecaspore or zoospore (of an alga), a production which so resembles the green-coloured Infusoria that Mr Pritchard states we have no means of dis-

---

1 Annalen des Sciences, 1840. 2 Essay on Parthenogenesis, p. 67. Ed. 1849. 3 Archives für Naturgeschichte, for 1846. tinguishing between the two. It equally produces by the fission of its endochrome or green contents. M. Thuret has shown how close is the analogy between the reproductive bodies of Coniferae and those of the green animalcules. He regards the Tetrasporae, although ranked with the Algae, as of very doubtful vegetable nature. The movements of the animalcular genus Diselmis resemble those of zoospores, and the species equally turn to the light, under the influence of which, like algae, they act upon the atmospheric air, disengaging a gas (oxygen?) when exposed to the rays of the sun. In a particular stage of one species, a very clear red spot was discernible, and a central globe closely resembling the amyloids granules so common in the cells of algae. It is the prevalence of the coloured speck in Diselmis Duvalii which, according to M. Joly, is the chief cause of the red colour so frequently observed over a large space of water in the Mediterranean Sea.

Whatever may be the special mode of generative increase among animalcules, their vast and rapid accumulation is as undoubted as extraordinary. Even among the Rotifera, direct observation has shown that a single individual will give rise to one million in ten days, and to sixteen millions in little more than a fortnight. If the children follow the footsteps of the parent, it is not easy to say what another fortnight might produce. Among the Polygastrica, the increase is still more speedy, one million having been produced from a single individual in seven days. Good and substantial food is, however, an essential condition of this rapid development; and when we consider what minute mouthfuls must suffice, we may the more easily conceive how rich a provender is spread before them in those innumerable infusions of animal and vegetable matters contained in almost all liquids. Fuchs has made some curious observations on the animalcules of cow's milk. He there finds in abundance two monadial species. He states that the blueness of milk is owing to the development and increase of an infusorial being, which he calls Vibrio cyanogenus. Under the name of Vibrio xanthogenus he defines another species, which he alleges makes milk turn yellow. Ehrenberg is of opinion that, in accordance with certain laws of nature, "living organisms," such as animalcules, may be developed in the air. The region of atmospheric dust is of vast extent, and ascends above 14,000 feet; and he conceives that its phenomena cannot be traced to mineral matters from the earth, nor to materials floating in space, nor to atmospheric currents, but rather bear relation to some general law of our atmosphere, in accordance with which there is a development within it of living organisms. The quantity of actual matter of this kind which falls from the air upon our earth is enormous, in consequence of the vast surface which it covers, however thinly. Meteorites, although comparatively solid and massive, are as nothing compared with it. It has been calculated, that of atmospheric stones there fell, from 1790 to 1819, 600 cwt.; whereas a single dust-shower, which was deposited at Lyons in 1846, is estimated at 7200 cwt. As these showers have been numerous over the whole earth, Ehrenberg asks, how many millions of tons weight of animalcular beings have fallen since the time of Homer? Important results have been deduced from the examination of the animalcular dust which falls at sea, as well as on land, in the determination of the direction of atmospheric currents.

Whatever defects may exist in Ehrenberg's system of arrangement, in consequence of some fallacies in his mode of viewing the organic structure and physiological functions of these extraordinary beings, there is no doubt that we owe to him many important observations and discoveries. He has especially pointed out the great influence exercised by these minutest of beings in the actual structure of the solid crust of the earth. He has satisfied both himself and others that the calcareous rocks of Syria and of Central North America contain densely crowded masses of small Polytalamic, several species of which, from the limestone of the New World, are identical with those of the European chalk. He has found the plastic marl of Ægina to consist of organisms, several of which pertain to the animalcules of the chalk. Limeberg Heath is described as a great bed of Infusoria; and one of the largest deposits yet known is near Berlin, in which it is remarkable that species still living, but not hitherto discovered at the surface of the soil, are found among the fossil species. Quekett has recorded that an infusorial stratum, twenty feet in thickness, underlies the city of Richmond in Virginia, and that several of the forms agree specifically with those found in the North Sea. Abundance of microscopic shields belonging to marine Infusoria (both the siliceous-shelled Polygastrica, and the calcareous-shelled Polytalamic) occur in the deposits of the Elbe, near Hamburg and Glückstadt. Similar results were yielded by the mud of the Scheldt, and by marine deposits on the shores of the North Sea and Baltic. Ehrenberg has well shown the enormous proportionate extent and intensity of life in the highest latitudes both north and south, and at the greatest attainable depth of the ocean.

So prodigious are the aggregations of these smallest forms of life, that they have actually raised, and are still raising, vast tracts of land from the bottom of the sea. Our antarctic voyagers have informed us that the waters of the ocean, between the parallels of 60° and 80° south latitude, are of a pale ochre-brown colour, in consequence of the enormous accumulation of these the frailest and yet least perishable parts of creation. Their death and decomposition have, we know not in the course of how long a period, actually produced a submarine bank or deposit of such vast dimensions, as to occupy an area of 400 miles long by 120 wide, flanking, as Dr Joseph Hooker has informed us, the entire length of the Victoria Reef.

Among the more singular localities of the Infusoria may be mentioned, not only meteoric dust, already noticed, but volcanic ashes, and other precipitations from the atmosphere. Ehrenberg has also shown that the blood-red spots which, to the terror of the superstitious, sometimes appear on bread and other substances, are occasioned by the surprisingly rapid development of an animalcule called Monas prodigiosa. He further supposes that one of the miracles in Egypt, recorded by the great lawgiver of the Jews, of the turning of water into blood, was produced, humanly speaking, by means of Euglena sanquinea (Ascari viridis of Müller, for it is sometimes green), or by the use of another species called Astasia haematodes.

The character of the lorica, or somewhat shelly covering, differs in its nature and composition in the different genera; being in some entirely siliceous, in others, composed of lime, combined with carbonic acid as a carbonate, with a portion of the oxide of iron. As in many of the smaller genera it is difficult to ascertain whether they are enclosed in a lorica or not, we may here state Mr Pritchard's mode of ascertaining the existence of that character. Having obtained some specimens, say of the family Cryptomonas, he places a drop of water containing them in a compressor or crush-box, mixing a little colouring matter with the water. If the species are loricated, a clear transparent ring will be observed under the microscope, encircling the animalcules, and seeming to keep them separate from the fluid in which they are immersed. Should this test prove unsatisfactory or insufficient, then the cover of the box may be pressed down, so as to

---

1 A complete history of showers of meteoric dust will be found in Ehrenberg's Passat-Staub und Blät-Regen, of which a brief abstract is given in Pritchard's Infusorial Animalcules, p. 89. 2 Infusorial Animalcules, p. 13. crush the specimens, when the coloured fluid will enter and surround their bodies; and, by a proper and expert management of the illumination of the microscope, the broken edges of the lorica will become visible.

The unfixed condition of opinion regarding infusorial animalcules is curiously indicated by the fact, that many careful and assiduous observers, such as Bauer, Leuckhart, Agassiz, and Reichenbach, deny the very existence of these creatures as a class, and maintain that they are mostly the embryonic forms of other and more highly organized beings. We doubt not that the opinion expressed in our preceding article, that our knowledge of this "invisible world" is in its infancy, is still correct, and that as the telescope brings forth stars from their nebular darkness, so the further the light of our microscopic knowledge penetrates into the obscure depth of the animalcular kingdom, the more clearly we shall have its now component parts resolved into definite forms of another nature than we at present suppose them. But that they are all merely embryonic forms, is doubtless a most visionary view, as no reason can be assigned a priori that beings, however small, are either uncertain or transitional, or that completion and finality of form are in any way inconsistent with excessive minuteness. One lesson may assuredly be drawn from the difficulties which beset the subject,—to avoid dogmatism, and hear in mind how unable we often are to solve the question, "What is truth?" But the extraordinary mutability of form and outward aspect of those frail creatures is no argument against their fixity of specific character within a certain range of variation, however wide. We know how different are the individuals even of some of the higher species from each other, under different circumstances, and at different stages of their life; but when once under our eye, they may be made cognizable to the senses of an observant person, under all their phases; that is, they may be identified with certainty from time to time. But with many animalcular beings it is not so. We see them once, as the astronomer may see some "bright particular star:" but we cannot calculate their erratic and changing course of life; and thus they may be either seen again no more for ever, or be observed under an altered aspect by another observer, and recorded with new characters under a different name. These, and such-like causes, may easily be conceived to operate disadvantageously against our speedy acquirement of assured knowledge regarding the animalcular tribes. But by means of patient and discriminating investigation on our own parts, a candid consideration of the observations of others, and an unbiased record of whatever has been clearly ascertained, there is no reason why the subject should not be gradually advanced so as to take rank with other branches of a less ambiguous nature. The general reader will not wonder at the state of uncertainty which still pervades our notions of many animalcules, when we mention, as an example of extreme minuteness, Monas crepusculum, of which the number occupying the space of a grain of mustard seed, one-tenth of an inch in diameter, has been calculated at eight millions!

Ehrenberg's great group of polygastric animalcules is primarily divided into Anentera (such as do not possess a true alimentary canal), and Enterodela (or such as are furnished with an alimentary canal). Here we are met by a noted antagonistic observer upon the very threshold.

"Recent investigations," says M. Agassiz, "upon the so-called Anentera, have satisfactorily shown, in my opinion, and in that of most competent observers, that this type of Ehrenberg's Polygastrica, without gastric cavities, and without an alimentary tube, are really plants belonging to the order of algae in the widest extension of this group; while most of the monad tribe are merely moveable germs of various kinds of other algae. As for the Enterodela—most of them, far from being perfect animals, are only germs in an early stage of development. The family of Vorticella exhibits so close a relation with the Bryozoa (cilio-brachiate polypes), and especially with the genus Pedicellina, that I have no doubt, that wherever Bryozoa should be placed, Vorticella should follow, and be ranked in the same division with them. The terminal group of Infusoria, Bursaria, Paramaecium, and the like, are, as I have satisfied myself by direct investigation, germs of fresh-water worms, some of which I have seen hatched from eggs of Planaria laid under my eyes."

Not only are authors on our present department opposed to each other, but (a rarer case) they seem in some instances to have no great confidence even in themselves. Thus M. Dujardin, one of the most trustworthy of the modern microscopic observers, after giving in a tabular form the characters of the groups which constitute the family Monadina, sums up by stating: "But these generic distinctions are entirely artificial, and simply intended to facilitate the naming of Infusoria one may meet with in such and such infusions, and which, when better known, may prove in some instances to be but varieties of a single species."

The preceding notices will suffice to show the still unsettled state of opinion regarding animalcules, and that Ehrenberg's system, although of great importance to the discriminating student, is not to be adopted implicitly as an assured exposition of the truth. We cannot here exhibit more of his arrangement than a compendious view of the family groups,—referring for details of genera and species to the work itself; and to others, with a list of which we shall conclude these supplementary observations.

**Tabular View of Ehrenberg's Arrangement.**

| Family | |-------------------------| | Monadina | | Cryptomonadina | | Hydromorina | | Volvocina | | Vibrioidea | | Closterina | | Astasidea | | Dinobryidea | | Amoebea | | Aecellina | | Bacillaria | | Cyclidina | | Peridinea |

1. *Annals of Natural History*, vol. vi. p. 156, 1850. Similar observations had been made by Mr Girard, who states that Kolpoda cucculus is an embryonic stage of a species of Planaria.

2. Die Infusorienthiere als vollkommene Organismen. Ein Blick in das tiefe Leben der organischen Natur. Atlas mit 64 illuminierten Kupfertafeln, gr. fol. Leipzig, 1838. We shall conclude by observing that some years ago an idea became prevalent that animalcules might be manufactured by means of galvanism. The results of some of the experiments proved too much, for the creatures when examined were found to belong, not to the Infusorial tribes, but to the Arachnides, a class more highly organized than even Insects. That the earlier naturalists, labouring under the disadvantage of imperfect glasses should have made mistakes is not surprising; but we read with wonder, in the year 1833, Dutrochet's statement that all the globular and elliptical Infusoria were merely vesicles set in motion by streams of electricity, and so might be artificially produced. In the following year Cagniard Latour declared that he had manufactured animalcules by means of carburetted hydrogen. But M. Audouin's examination proved that they were Entomostraca, and that the method employed in their production was fallacious. The following is Ehrenberg's account of some curious experiments on these imaginary productions by Professor Bondsoff, communicated to the German Naturalists' Association in 1834. If a solution of chloride of aluminum be dropped into a solution of potassa, by the attenuate solution of the aluminum in the excess of alkali, an appearance will be given to the drop of aluminate matter, by the chemical changes and reactions which take place, as if the Amoeba diffusa were actually present, both as to its form and evolutions, and it will seem to be alive. Such appearance, adds Bondsoff, bears the same relationship to the real animalcule as a doll or figure moved by mechanism does to a living child.

The English reader will consult with advantage Mr Prichard's History of Infusorial Animalcules, living and fossil: new edition, enlarged, Lond. 1852. A great mass of useful information is there collected, and Ehrenberg's system is given in detail. F. T. Kützing's Die Bieselschädigen Bacillarien od. Diatomaeen, 1844, is an excellent work. Dujardin's has been already named in full, as perhaps the best systematic work we have on animalcules at the present time. Mr Ralfs' recent monograph on the British Desmidaceae (Lond. 1848) will be found indispensable; as also the Rev. William Smith's Synopsis of the British Diatomaceae, vol. i. Lond. 1853.

The following is a list of papers published in the Annals of Natural History, from which much useful information will be gained:—On the existence of Infusoria in Plants; by Professor Morren; vol. vi. p. 344. On the Sacculi of Polygastrica; by Dr J. W. Griffiths; vol. xi. p. 438. On the production of Infusoria in the Stomachs of Herbivorous and Carnivorous Animals; by MM. Gruby and Delafond; vol. xiii. p. 154. On Microscopic Life in the Ocean; by Professor Ehrenberg; vol. xiv. p. 169. Abundant Occurrence of rare Infusoria in the Scallop; by H. Lee; vol. xv. p. 371. Microscopical Examination of the Chalk and Flint of the southeast of England; by Dr Mantell; vol. xvi. p. 73. On the Organization of the Polygastric Infusoria; by C. Eckhard; vol. xviii. p. 433. On Conjugation in the Diatomaceae; by G. H. K. Thwaites; vol. xx. pp. 9 and 343. On the Siliceous Polycystina of Barbadoes; by Professor Ehrenberg; vol. xx. p. 115.

The following papers are from the new series of the Annals:—On the British Lagenae; by W. C. Williamson; vol. i. p. 1. On the Diatomaceae; by G. H. K. Thwaites; vol. i. p. 161. On a new British Species of Campylococcus; by W. C. Williamson; vol. i. p. 321. Notes on Diatomaceae; by Professor Dickie; vol. i. p. 322. On Fossil Diatomaceae in Aberdeenshire; by Professor Dickie; vol. ii. p. 93. On a Diaceous Rotifer; by T. Brightwell; vol. ii. p. 153. On the colour of a Fresh-Water Loch; by Professor Dickie; vol. iii. p. 20. On the Mode of Growth in Oscillatoriae; by J. Ralfs; vol. iii. p. 39. Observations on Recent Foraminifera; by W. Clark; vol. iii. p. 380. On two new species of Floscularia; by Dr W. M. Dobie; vol. iv. p. 233. On the Development of Trichodina pediculus; by J. T. Arledge; vol. iv. p. 269. On the Conjugation of Closterium Ehrenbergii; by the Rev. W. Smith; vol. v. p. 1. On Deposits of Diatomaceous Earth on the shores of Lough Morne, county Antrim; by the Rev. W. Smith; vol. v. p. 121. On Nyctotherus, a new genus of Polygastrica; by Dr Leidy; vol. v. p. 156. On the Recent Foraminifera; by W. Clark; vol. v. p. 161. On the Nostochineae; by J. Ralfs; vol. v. 321. On Asplanchna priodonta; by P. H. Gosse; vol. vi. p. 18. Notes on the Diatomaceae, with descriptions of the British species included in the genera Campylococcus, Surirella, and Cymatopleura; by the Rev. W. Smith; vol. vii. p. 1. On three new species of Animalcules; by J. Alder; vol. vii. p. 426. On the Germination of the Spore in the Conjugates; by the Rev. W. Smith; vol. viii. p. 302. On the Cell-Membrane of Diatomaceous Shells; by J. W. Bailey; vol. viii. p. 157. Remarks on Dickieia; by J. Ralfs; vol. vii. p. 204. Catalogue of the Rotifers found in Britain, with descriptions of five new genera, and thirty-two new species; by P. H. Gosse; vol. viii. p. 197. On Chantasia; by J. Ralfs; vol. viii. p. 302. Notes on the Diatomaceae, with Descriptions of the British Species, included in the genus Pleurosigma; by the Rev. W. Smith; vol. ix. p. 1.

---

1 For example, the animal obtained by Mr Crosse by means of galvanism was an Acarus. It was afterwards stated to be a well-known species, common in houses, and not unlikely to make its accidental way into a philosophical apparatus.