When the word Zoophyte began to be used by naturalists, it designated a miscellaneous class of beings, which were believed to occupy the space between the animal and vegetable kingdoms, and in which the characteristics of the subjects of each met and were intermingled. They were of a "middle nature," not because of their outward resemblance to plants, but because they were deficient in the more obvious qualities of animals, and were apparently more influenced by exterior forces than by any volitions springing up within. Almost insensible and immotive, their weak and obscure life was merely regarded as one of vegetation, engendered in them by putrefaction or fermentation, and unsusceptible of the volitions and passions which move and agitate higher entities. Thus the term indicated a mingled life or constitution, and had no reference to figure; but some time after it had been allowed on all hands that the productions in question were "better than mere vegetables," another class of objects, hitherto supposed to be altogether vegetable, was ascertained to be of animal origin; and as their similitude to mosses and lichens, to seaweeds and mushrooms, was undeniable, and indeed so remarkable as to have long veiled their nature from us, so the term zoophyte was transferred to this newly discovered order, and has since been applied by the majority of English authors to it alone. With continental naturalists, however, the word has still its widest application, embracing, in their nomenclature, not merely those polypiferous beings which cover the bottom of the ocean with a singularly exact mimicry of vegetation, but also the star-fishes and sea-urchins, the sea-figs, and sea-nettles or jelly-fish, and even the intestinal worms. It is in this wide acceptation that the word is employed by Cuvier and Blainville; and we use it here with the same latitude, agreeably to the plan indicated in our article ANIMAL KINGDOM.
The zoophytes, then, as defined by Cuvier, form a sub-kingdom co-equal with the two divisions in the animal kingdom named Radiata and Acrata by Macleay. The classes included in it have less of a common resemblance than the classes of any other sub-kingdom, so that in the great variety of structures which they present to our study, we seek in vain for any one character that shall connect them together. The most general character is that which has conferred upon them the synonyme of "Radiated Animals," given because the organs of locomotion, and even the internal viscera, are arranged very often in a circular disposition round a centre, so as to give a sort of radiant appearance to the whole body, or to some part of it. The nervous system is at the best only rudimentary, and is demonstrable only in a few genera of three of the classes. Thus its existence has been shown in several species of intestinal worms, where it consists of one or two ganglions placed near the mouth, and from which diverge a few filaments, and one or two longer chords that follow down the length of the body. In the more normal zoophytes, the nervous system forms a circle round the oral aperture, whence slender filaments radiate towards the circumference, rarely dividing into a few branchlets, and losing themselves in the parenchyma long before they reach the periphery. But in the larger number of this sub-kingdom no trace of such a system is discoverable, unless, with Macleay, we find it in the "minute granulations" which bespeak their homogeneous, mobile, and irritable pulp, and "which may be considered as the nervous molecules dispersed over, or, as it were, confounded with, the substance of these animals, so as to im-
pregnate the whole with sensibility." This property of Zoophytes, animal life they accordingly enjoy in a high degree of development, while their instincts are reduced almost to a nullity; and, in regard to the external senses, it may with truth be said of most of them, that they are "sans teeth, sans eyes, sans taste, sans everything." They are, almost without exception, indolent and slow of movement, some advancing by the writhings and contractions of a soft body; some by the play of invisible cilia, which garnish, in set rows, their appendages; and others by the aid of hollow extensible tentacular suckers; while many among them are rooted, and as fixed as the plants whose graceful forms they seem to envy and strive to emulate.
There is, according to Cuvier, no true system of a circulation in any zoophyte; but Nordmann has delineated a very beautiful system of vessels, apparently sanguiferous, in some intestinal worms; and a similar one has been shown to exist in the Planariae, and in some external parasites, as in the genus Phylline. Among the more regular zoophytes, we find very generally a system of aqueducts, which permeate and ramify through the body, but which are distinguished from any circulatory vessels by having a direct communication with the water in which the animal floats. This system is mainly subservient to locomotion; but to a certain extent it must supply the purposes of a circulation in higher organisms, for the fresh currents of water which it leads within the body will oxygenate and render fit for assimilation the nutritive materials that come within their reach and influence. The Holothuriae afford a good illustration of this double function, for they have two aquiferous systems—one connected with the intestines, and in correspondence with the organs of respiration; the other subservient only to the turgescency and relaxation of the organs that perform the offices of feet. This latter system only, it is said, can be discovered in the star-fishes and sea-urchins; while the vascular canals that ramify like veins through the clear gelatinous bodies of the sea-jellies, originating in the alimentary cavities, and running in divergent lines to the circumference, seem to constitute a system accessory principally to respiration and nutrition. In many fixed polypiferous zoophytes, there are also found ducts for introducing water within the body; and in others, where these aquiferous ducts have no existence, the surface or appendages of the little creature are clothed with minute vibratile cilia, that constitute a real breathing apparatus.
Some families, such as the holothuriae, the sea-urchins, and several intestinal worms, as well as some polypiferous zoophytes, have a mouth, an alimentary canal, and an excrementitious or anal orifice; others have a kind of stomach with only one orifice, which is by turns a mouth and a vent; in a great number there is merely a digestive cavity, excavated in the substance of the body for the reception of the food, which enters sometimes by one and sometimes by several orifices; and in other zoophytes of abnormal character there is no mouth, and we suppose that these must imbibe their nutritive matter by pores on the general surface.
The individuals of some species of intestinal worms are male and female, but in general the zoophytes are hermaphroditical and oviparous. Some are propagated by a sort of gemination, or by self-division. Many of them are compound animals—a kind of monster, in which often hundreds of individuals consociate, and are organically connected together, so as to make one living mass or commonwealth,
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1 "Imperfecta veteribus, nec inepte, dicta animantia, destituntur capite, auribus, naso, oculis, plerique pedibus; ab insectis itaque diversissima, a quibus dudum removit naturae cryptogama." (Linnaei Systema Naturae, 1069.) Intestinal that possesses all things in common, and usually shoots up in an arborescent form.
Having premised these few remarks, we proceed to treat of this sub-kingdom under the following divisions or classes:—I. Intestinal Worms; II. Echinodermata or Sea-stars; III. Aculepthe or Sea-jellies; IV. Polyps, or Zoophytes properly so called; V. Rhizopods; VI. Sponges; and VII. Lithophytes.
In addition to the true Zoophytes and the remaining classes of the sub-kingdom Radiata, some members of the sub-kingdom Articulata have been treated of in this article, which was written for the seventh edition of the Encyclopaedia Britannica by that able naturalist the late Dr George Johnston, whose useful labours amongst the lower orders of animals are well known to the scientific world. The Entozoa or intestinal worms are now considered a class of the Articulata, whilst the Epizoa are looked upon as members of the class Crustacea. Higher in the scale than all the rest are the Polyzoa, which are now placed near tunicated animals in the sub-kingdom Molusca. The additions made in this reprint of the original article are indicated by being placed between brackets. The Infusoria have been treated of under that title. Lithophytes belong to the vegetable kingdom.*
I.—INTESTINAL WORMS.*
(Entozoa: Enteinthia.)
It affords a striking illustration of the wide diffusion of animal life to have ascertained the fact, that almost every species of the vertebrate orders, and very many of the inferior classes, afford, either within or on the surface of the body, a place of nativity and domicile to one or more living creatures, framed with especial adaptation to the circumstances of their destined abodes. They do not, however, infest every animal indiscriminately; for, on the contrary, the parasites of almost every species are peculiar to itself, or they are confined to a few of analogous habits and structure. There are some partial exceptions. Thus, the fluke (Distoma hepaticum), so common in the liver and gall-ducks of sheep and other domestic cattle, is found occasionally in the liver of man, but comparatively so small as to have been sometimes looked upon as a distinct species. The Ascaris lumbricoides of man is identical with that found in the horse, the ox, and the sow; his Trichopcephalus occurs in the ape; the Cysticercus of the cellular tissue is common to him and the ape and pig; and the Strongylus giganteus has a wide range, not fearing man, and rioting in the kidney of many of the inferior animals. Frelich took from a tropical parrot an Ascaris, which was apparently identical with a worm that Rudolphi found in our domestic pigeon; and similar examples, more especially from among the parasites of fishes, might be instanced. But there is no example of a worm being common to a warm and a cold blooded animal; nor does the same worm ever occur in the mammalia and in birds, nor in amphibia and in fishes; nor, indeed, in the species of any two well-distinguished classes; and so also it is ascertained that the parasites of the carnivorous animals (with the sole exception of the renal parasites) are in every instance different in kind from those of the vegetable feeders.
It must not, however, be concluded, that of the animals liable to the attacks of intestinal worms, every individual is vermigerous. On the contrary, the Entozoa in general are comparatively of rare occurrence, and many are so rare that few helminthologists, of however wide research, have ever met with them. Mr Lawrence has seen a female, who from time to time has voided many hundreds of small worms (Spiroptera hominis) from the urinary bladder; but, so far as is known, no other human being was ever so afflicted. Goeze found in the boar a Trichopcephalus, which Rudolphi has sought for in vain both in wild and domestic swine; and he tells us he had dissected innumerable mice in a fruitless search after their Trichopcephalus, described also by the first-named naturalist. These are undoubtedly extreme cases, but they place in a strong light the partial and accidental diffusion of these creatures. What circumstances determine them to select one individual in preference to another are unknown, though reasons enough have been stated, of all which it may be safely said that the facts adverse to their admission are almost as many as those in their favour. There is no denying that worms in general often infest the delicate and sickly; that youth is favourable to the evolution of some, and maturity to that of others; and females may be more verminous than males; but the contraries are numerous, and the lovers of statistics have not yet balanced the proportions. A crude farinaceous diet has been much blamed, and we should suppose justly; yet the poor of Scotland, who subsist much on such a diet, are not more wormy than the better fed poor of England. Rich moist pastures are said to be favourable to the generation of the fluke in our sheep and cattle; but this is only the case with some pastures, which, in every district, have acquired this bad pre-eminence, and on which certainly our herds cannot be fed many days without the certainty of being tainted. Salt pastures are, on the contrary, unfavourable or destructive to the fluke and worms in general; nor in man does any cause apparently more certainly predispose the body to their visitation than an unsalted immitive diet. "Salt," says Dr Paris, "when taken in moderate quantities, promotes, while in excessive ones it prevents, digestion: it is therefore tonic and anthelmintic, correcting that disordered state of the bowels which favours the propagation of worms." And as an instance of the results of its want, Lord Somerville adduces a punishment which formerly existed in Holland. "The ancient laws of that country ordained men to be kept on bread alone, unmixed with salt, as the severest punishment that could be inflicted upon them in their moist climate; the effect was horrible: these wretched criminals are said to have been devoured by worms engendered in their own stomachs."
The extrinsic causes which give a predisposition to worms are as little known as those which act immediately on the body. Very few avertebrated animals are vermiparous, while there is probably no species of vertebrate that is exempted from parasites. Of the latter class, such species as have been reduced to domesticity, or are retained captive, are more subject to worms than the wild and untamed; and fishes appear to be pre-eminently infested with them. It is not yet determined that the same parasites infest the same animals in different and remote countries, although this is probably the case; but a few facts, relating principally to the human species, seem to prove that climate has a certain influence over their generation. The Filaria medinensis, or Guinea-worm, is only found under the torrid zone, in Asia and Africa; and the Furia infernalis is peculiar to Lapland. Ascarides prevail to such an extent in Abyssinia, as to regulate in some degree the movements
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* [On the subject of the Entozoa the reader may consult the following works in addition to those hereafter cited:—"Goodsir on the development, structure, and economy of the Acephalo cysts," Trans. Roy. Soc., Edinb. 1844; Dujardin's Histoire Naturelle des Helmintes, 1845; Prof. Owen's Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals, 1853; Dr P. J. van Beneden's Memoire sur les Vers Intestinaux, 28 plates, Paris, 1858.]
* Of upwards of 200 species examined by Dr Bellingham, several occurred in six, others in ten, and one in fifteen different animals.
* Medico-Chirurg. Trans., ii. p. 382; Cyclop. of Anat. and Physiology, ii. p. 124.
* Ext. Hist. Nat., ii. part ii, pp. 96, 97.
* Rudolphi considers the Furia an apocryphal animal, but in favour of its existence we have to add to the testimony of Linnaeus and Solander that of Dr E. D. Clarke (Travels in Scandinavia, part i. p. 208). Intestinal of the inhabitants; and in the West India Islands, intestinal worms in general are much more common than they are in Europe. We know, on the evidence of Vallisnerius, that *Ascarides* are very frequent in the calves of Italy; while those born from the cows of Germany, says Rudolphi, are rarely infected with them. Hasselquist tells us that when in Cairo he was told that three-fourths of the inhabitants were diseased with *Taenia solium*; and "I have been informed by my friend Dr Knox," says Dr Hodgkin, "that our troops which were stationed in and near the Cape were generally infested by these animals." Egypt and Africa may then perhaps be considered as the lands of choice of this *Tænia*, which, however, has spread, though in smaller numbers, over Germany, Holland, England, and France. In the latter country it occurs, but not simultaneously in the same individual, with the *Tænia lata*, Linn.—a species of extreme rarity in the English, Dutch, and Germans, but very common in the natives of Switzerland and Russia.
If any evidence can be drawn from the silence of Otho Fabricius, it would seem that the Greenlanders are not subjected to the tape-worm, but they breed the Ascarides abundantly.
Intestinal worms, as their name implies, are found principally in the alimentary canal, and the viscera subservient to its functions. There are species, however, which have their appropriated seats in the cellular and adipose and serous tissues, and in the parenchyma of the most secret organs. One species peoples in myriads the voluntary muscles, and more than one has penetrated the heart; several develop themselves in the lungs and air-passages, in the liver, the kidneys, and the brain; one or more have entered the blood-vessels or aneurismal tumors connected with them; some float in the humours of the eye; and more than one loathly worm bathes unharmed in the acrid excretion of the urinary organs. If indeed we except the bones, the cartilages, and ligaments, no organ seems exempted from the occasional attacks of worms, unless it be the spleen, in which, according to Rudolphi, no worm has yet been discovered ever to take up its abode. These parasites may in one sense be considered as accidental, since they are found in certain individuals only of the species they infest; and there can be no doubt, although their evil deeds have been frequently much exaggerated, that they become not seldom the cause of serious or fatal disease.
And here we may cursorily notice an opinion which has found its advocates in every period of the history of medicine, that most contagious diseases, fevers, and plagues, originate from animalcules introduced into the body, and are propagated by their communication to other bodies through the medium of the atmosphere. Linnaeus was a believer in this hypothesis, which has recently been supported, with much ingenuity, by Dr Holland, who, however, properly remarks, that "though the course of discovery has recently been approaching, in some points, nearer to the hypothesis in question, it still furnishes nothing beyond stronger presumptions and more numerous analogies" in its favour.
If animalcules can be so pernicious—and we admit that no more probable cause of many pestilences, and especially of cholera, has been assigned—their influence is, according to physiologists, more than counterpoised by the share which another class of them has in the continuance and propagation of the species. This class is by naturalists named the *Spermatozoa*, of constant and invariable presence in the seminal fluid of every animal capable of propagating its kind; but they are absent in that of the mule, and of other animals which may be sterile from age or the season of the year.
Like the accidental Entozoa, the Spermatozoa of every animal has its peculiar characteristics, but the differences between them are comparatively slight. "They all agree in having slightly oblong and flattened heads, with lengthened tails, tapering so as to become nearly or quite invisible with the best glasses; they possess active powers of motion, and are evidently endowed with sensation. No trace of organization has yet been discovered in them, probably on account of their extreme minuteness. Whether essential to generation or not, they may be regarded as the parasites of the tubuli seminiferi."
The origin of the Entozoa within animal bodies, and their viscera, has for long been the subject of much debate and curious speculation. It was a hasty disposal of the question to say that they were no other than the worms of stagnant waters, of marshes, and of vegetable roots, introduced within the body, either in their perfect or egg state, but altered in their appearance and character by the genial heat and other novel circumstances by which they were now surrounded. Though this explanation had the support of Linnaeus, and has lately found a strenuous advocate in one of the most learned men that ever graced the medical profession, it has been long known to be quite untenable; for no fact is better ascertained than that intestinal worms are found solely in animal bodies, where only they can live and propagate. The instances to the contrary which have been alleged, of tape-worms and flukes living in marshes, and of earth-worms in our bowels, are known to rest on fiction or incorrect observation; so that, in the discussion of the question, it must be assumed as a fact, that the worms are born in, and peculiar to, the places where we find them. This assumption presented no difficulty to the earlier naturalists, who were unanimous in the belief that all worms were the results of a putrefactive process;
putrefaction into life ferments, And breathes destructive myriads; or of spontaneous generation; the spawn of a superabundant phlegm, vivified by the heat and fermentation of the belly. But to this ancient doctrine the experiments of Redi on the generation of insects gave the death-blow.
To explain the beginning of these worms within the body on the common doctrine that all created beings proceed from their likes, or a primordial egg, is indeed so difficult, that the moderns have been driven to speculate, as our fathers did, on their spontaneous birth; but they have revived the hypothesis with some modification. Thus, it is not from putrefaction or fermentation that the Entozoa are born, for both of these processes are rather fatal to their existence, but from the aggregation and fit apposition of matter which is already organised, or has been thrown from organised surfaces. Thus Buffon applied his doctrine concerning organic molecules to account for their genesis. Milk, he tells us, "consists entirely of organic and prolific matter, which, when not properly digested by the stomach, and applied to the nourishment and growth of the body, assumes, by its natural activity, other forms, and produces animated beings or worms;" hence their commonness in the bowels of children; and their origin in the most hidden organs has the same source, for the "living organic particles" may, from various causes, be forced too abundantly to any part of the frame, and living creatures in that part are the result of their union. Rudolphi has adopted an opinion
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1 Lectures on Morbid Anatomy, vol. i. p. 200. 2 Rudolphi, Entoz. Hist., ii. part ii. p. 72, comp. p. 162. 3 On Animals in the Blood; see the Lancet for August 1840, p. 778. 4 Hodgkin's Lectures, vol. i. p. 213. On these animated bodies the reader will find ample information in Blainville's Manuel d'Actino- logie, 573, &c. 5 Of various hypotheses of the earlier writers Le Clez has given an excellent account in his chapter xiv., "On the Origin of Worms in Animal Bodies." (History of Worms, trans. p. 329, &c.) Intestinal very similar to that of Buffon; for it appears to him that Worms, the objections which their history furnishes to a belief in their sexual propagation are insurmountable, and that we must of necessity believe in their spontaneous appearance, or rather in their production from the fit apposition of organic particles that have not been assimilated with the parent body, or from the separation from it of organized particles, which, retaining their proper life, become the germs of an entozoon in situations and under circumstances favourable for their development and metamorphosis. Their origin in this manner is not more wonderful, or more inexplicable, than that of many of the inferior animals from sections of themselves. The Nais, the Planaria, and the Hydra, furnish examples of animals of as perfect organization as worms being thus propagated; for if a small portion is cut away from any species of these genera, and placed in a suitable position, it will continue to live and grow, and develop new organs, until it has acquired in every respect the form and structure and habits of the animal from whence it was separated. Now particles of matter fitted by digestion, and their transmission through a living body, for immediate assimilation with it, or flakes of lymph detached from surfaces already organised, seem neither to exceed nor fall below that simplicity of structure which favours this wonderful development; and the supposition that, like the morsels of a Planaria, they may also, when retained in contact with living parts, and in other favourable circumstances, continue to live and be gradually changed into creatures of analogous conformation, is surely not so absurd as to be brought into comparison with the metamorphoses of Ovid. It is a speculation fairly open to inquiry; and indeed one main argument in favour of the spontaneous generation of Entozoa, is the admitted inadequacy of all other hypotheses to explain the facts. Is it possible to believe of a worm which has been found, during the nineteen centuries of the world's age, in one or a few individuals only, that its eggs can have been transmitted from generation to generation, and be thus so very rare in its perfect state? But we have one proof at least that a change of condition in an animal is capable of generating a worm, for a good authority assures us that a parasite found in the flesh of the domestic swine is not to be found in the wild race; and Dr Jenner ascertained that he could produce hydatids and fluke-worms at will in rabbits, by feeding them solely on green succulent food.
How but from innate workings are we to explain the first origin of worms that have neither sensual organs nor ova, but, like the hydatid, increase from buds that pullulate from the inner surface of the vesicle that contains them? And Rudolph has even seen what he believed to be young nascent Taeniae germinating from the villous surface of the bowels. We think the hypothesis is supported also in some degree by the fact, that the origin of Entozoa in general is favoured by all causes which tend to disturb the equality between the secerning and absorbent systems. Thus there is great reason to believe that some inflammatory action of the liver, of the eye, and of other wormed viscus, precedes the evolution of parasites in them; and it is well known that a morbid state of the alimentary canal, especially an abundant secretion of unhealthy mucus, is connected with the production and increase of all intestinal worms, so much so that Broussais believes an inflammatory state of the mucous membrane to be even an essential condition to their existence. It is obviously necessary to suppose that there are unknown conditions or laws regulating this the spontaneous growth of worms within us, so that a certain uniformity in the products is the result; but it seems not more difficult to admit the existence of such laws, overruling the destiny of unappropriated organic matter, than their existence and rule over the shred of a Planaria severed from another's body. That there are such laws of regulation, we infer from the fact that the detached portions of a Planaria, a Hydra, or a Nais, invariably evolve into their respective species; and from the analogous fact that the worms of the different cavities and textures are usually dissimilar, as might have been expected from the dissimilarity in the structures from which their unformed and unseminated embryos are separated.
The variety in the exterior forms of intestinal worms is sufficiently great to form the basis of their classification into subordinate divisions. Thus we have the round or cylindrical worms (Nematoidae); the saciform, with prickly proboscides (Acanthocephala); the flat or fluke-worms (Trematoda); the tape-worms (Cestoidae); and the cystic or hydatids (Cyctida). In very few of them are there any external appendages, either to diffuse or heighten their sensibilities and perceptions, or to assist in locomotion; but we can distinguish in all of them a head, a body, and an anal extremity; in some there is a neck; in the Trematodes, one or two ventral suckers; and in some the organs of generation are protruded. The skin is commonly white, smooth, thin, and moist, but coriaceous in many of the Acanthocephala, and sometimes roughened with reverted prickle. Minute black points, suspected to be visual organs, bespeckle the anterior extremity of some non-parasitical genera (Planariae), often classified with the flukes; and similar specks have been discovered on a few true Entozoa at certain stages of their development. Thus they are of a brilliant lustre in the Phanoglenae and Enchelidium; and traces of them are visible in the Gyrodactylus auricularis, in several Cercariae, in the Polystoma integerrimum, in the young of many Distomae, Monostome, and Amphistome, and in the Scolex polymorphus.
The internal structure of the Entozoa is as various as their outward form, and in some degree of harmony with it, as will be proved when we come to explain the characters of their classification. It ranges from a homogeneous structureless tissue, such as composes the whole of a zoospore, to that of an animal with organs of defined limits and function, such as we find them in a nematoid-worm, where there are distinct muscles, a perfected apparatus of digestion, and a system of generation on male and female individuals. In a very few intestinal worms, anatomists have recently demonstrated the existence of a slightly developed nervous system. In others, there exists a system of vessels, in which an obscure circulation of a colourless fluid has been seen; but in none of the class is there any trace of a distinct respiratory organ, the functions of which are performed by the skin or surface. The genera whose habitat is the alimentary canal, may have a slightly oxy-
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1 *Cycticercus cellulosae*: "The fact of its being found in the swine which man has domesticated, and not in the wild race, appears to furnish an instance of organised bodies which have been formed long after the general creation." (Blumenbach's *Elsae. of Nat. History*, trans., p. 243.) The fact has been contradicted, but the history of insects and infusory animalcules furnishes us with many similar, so that the argument is not invalidated.
2 *Cyctop., of Pract. Medicine*, vol. ii. p. 438.
3 The reader will find the subject discussed at great length by Rudolph in cap. xviii. of his *Historia Nat. Entozoorum*, vol. i. pp. 370-416.
4 The Phanoglenae, which lives in the larva of some neuropterous insects, has some prolongations like antennae; and Diesing has described some genera (*Ancyraconthia*, *Heterocollis*) with heads furnished with filaments of various forms.
5 Lamarck's *Anim. sans Vert.*, iii. p. 546, note 1, 2d edit.
6 Respiratory trachea, similar to those of insects, have been ascribed to some of the nematoid worms, but erroneously. See Rudolph, *Entoz. Synopsis*, p. 579, &c. intestinal genated atmosphere to breathe; but such as live in the muscles, in the humours of the eye, or in the brain, no uncombined air can reach; and we are forced to conclude that all the oxygen they require for existence is communicated to them through the fluids they feed on, or from the blood as it circulates over the surfaces with which they are contiguous, or from the medium in which they float. They doubtless require but a small supply, for the heat that is involved by respiration in other animals is here furnished by the warm abodes they live in; and their food, consisting of chyle, lymph, and excretions in a recent state, is already half prepared for assimilation. We know that their food must be of this soft and liquid nature; for many worms, having no oral aperture, seem to imbibe all their nutriment through minute pores in the skin, or by the process of endosmosis; and the whole of what they imbibe is probably assimilated. Even in such worms as have a mouth, this is never armed with cutting or triturating instruments, but constitutes a simple pore for the entrance of a soft material upon which suction can operate. As in the nematoid worms there is both a mouth and an anus, we may conclude, that of their food some part is feculent and excrementitious; and the same inference may be made from every species of similar structure. The Trematoda or flukes have no anus, and their mouth is certainly ill defined, but they have an alimentary canal, ramified in a dendritic fashion; and Rudolph believes it to be proved, by the colour of the matter in these vessels, that their food is also partly excrementitious, for the worm, naturally colourless, is often dusky, or variously tinctured by the nature of its food. It is singular that this order appears to receive no part of its nourishment from cutaneous absorption, a mode of supply very general in the class, and especially remarkable in the order Acanthocephala. When a specimen of an Echinorhynchus is taken fresh from the bowels, it is small, flattish, and flaccid; but shortly after being immersed in a glass of water, it has become larger, swollen, and distended like a sac; and the most conclusive experiments have proved that the water of distention could only have passed inwards through the skin, the structure of which is peculiarly adapted to the office. If any part of the skin of the Echinorhynchus gigas is held up opposite to the light, and examined from the internal side with a common lens, we perceive a remarkably elegant net-work of vessels, sprinkled over with minute pearl-like vesicles, which are, as it were, the centres of the anastomosing branchlets, or perhaps merely dilatations of the vessels at their points of coalescence and union.
The nematoid and acanthocephalous worms have distinct sexes; but the Trematoda and many Cestoidae are androgynous, that is, each individual of the species possesses the organs peculiar to both sexes, and may of itself fecundate its ova, although, with regard to some of them, it has been supposed that the union of two individuals is necessary, as is the case with the slug and snail. In other worms, the female or reproductive organs exist alone; and in the cystic Entozoa no generative apparatus has been provided. "They would seem to be gemmiparous, and to have the reproductive power diffused over the whole cyst, at least in the Acephalocysts, in which the young are not developed from any special organ, or limited to any particular part of the cyst."
The great majority of the higher Entozoa are oviparous; but we have several exceptions among the Nematoids, and one at least among the fluke-worms, which are viviparous. The distinction is however immaterial, for in both kinds the ovaries possess a similar structure, and the eggs accumulate in them in the same fashion. In the oviducts of the viviparous Cucullanus, as of the oviparous Echinorhynchus, there are found the same bodies which Rudolph conjectures to be cotyledons, or little placentae, into which the ovules are fixed, so that even in this respect no difference exists. The ovules of the oviparous species are of two kinds, containing either an undeveloped and inconspicuous embryo, or one that is fully formed, but motionless. The ovules of the viviparous species, on the other hand, contain a moveable embryo.
The number of ova produced by a single worm is sometimes prodigious, and almost incredible. *Ascaris lumbricoides* contains, when pregnant, many thousands; *Ascaris nigrovenosa*, according to Goeze, may have 700 living young at a birth; and the *Cucullanus* as many. But what are these to the calculations of Dujardin, who supposes that one *Taenia serrata*, with its 200 articulations, may contain in the united chain not less than twenty-five millions of ova! And it is in fact not uncommon to find eight or ten of these productive monsters in one poor dog. From this fertility we might conclude the numbers within the body of those animals which they infested would be fearfully great; but this is seldom the case, and least of all with those very species that we have instanced as so marvellous in their productive powers. The *Taenia* or tape-worm is often solitary, and rarely numerous in any individual. It is not difficult to reconcile this apparent contradiction of means and end, when we call to recollection the numerous accidents to which both worms and eggs are exposed, from the nature of their sites; how many undeveloped ova, how many young, how many adults, must daily pass away.
We have already slightly indicated the diseases that may arise from their presence and multiplicity, an injury that some physico-theologists would fain persuade us is counterbalanced by a series of benefits that animals derive from their parasites. One gravely tells us, that by their motions they cause a gentle irritation in aid of the intestinal functions, which, moreover, may stimulate the other viscera to the discharge of their duties, and prevent their falling into a state of inaction favourable to the commencement and increase of organic diseases. Another insists that the Entozoa drink up the superabundant chyme, chyle, or mucus, in the bowels. Another believes that they were created as a wholesome check on the pride and vanity of man, as trials of his patience and other virtues, and "finally to secure to him an entrance into an immutable and eternal state of felicity when that of probation is at an end, so that the gates of death may be to him the gates of peace and rest." Now it may be commendable to look for good in everything; but this, we think, is looking rather too far, looking also into a sort of kaleidoscope, in which we see all beautiful though unstable pictures patterned out of worthless things.
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1 M. Chevreul, however, found no oxygen in the gas of either the small or great Intestines of three different subjects. See Boasock's Physiology, vol. ii. p. 490. 2 Dr Drummond doubts whether the colour is dependent on the contents of the intestine. "It is certain that in a mass of individuals (of Echinorhynchus acus) found in the same portion of intestine, considerable diversity of colour prevails; and where there has been only a transparent mucus present, I have found specimens of a pure white, and others of a bright orange." Mag. of Nat. Hist., n.s., ii. p. 519. 3 Rudolph, Entoz. Synopsis, p. 582. See also Owen in Cyclop. of Anat. and Phys., ii. p. 126, and Drummond in Charlesworth's Mag. of Nat. Hist., ii. p. 517, 518. 4 Ann. des Sciences Nat., n.s., vol. x. p. 34. And so of *Filaria mediterranea* Rudolph writes: "Filariae nostrae prole quasi faretse sunt; quod si barum longitudinem illius vero minime spectas, fastuam multa millium millia singulis tribue." 5 Kirby's Bridgewater Treatise, vol. i. p. 331. The relationship of the Entozoa with other animals is involved in much obscurity, but we cannot therefore concur with Bär in his proposal to exclude them from a natural classification of the animal kingdom; nor do we exactly understand Rudolph's notion when he says they constitute a peculiar fauna, rather than any order or class parallel with the ordinary divisions of systematists. If the zoospores are to be reckoned distinct beings, they must probably go to throng the chaos of infusory animalcules; and Dujardin has discovered in the earth-worm and in the slugs a parasite (Albertia) that combines with the structure and habits of an entozoon many of the peculiarities of the rotatory animalcules. The hydatis may represent the hydraform polypes; the tape-worm the Cestum veneris of the gelatinous medusa; the Acanthocephala have some exterior resemblance to the sipunculoid genera of the radiated animals; the Nematoids, a nearer one to the Annelides; and the Trematoda have, with a very general yet erroneous assent, been made members of a family that embraces the Planaria—leech-like natives of fresh and salt waters—which Mr Swainson errs no less in arranging with the mollusca. Their affinities being thus so remote and uncertain, we are not surprised to find the classification of the intestine unsettled; but from among the many that have been proposed, we only select two for exposition here; that, namely, of Rudolph, which has been most generally approved; and that of Cuvier, for this, from its wider scope, will afford us an opportunity of noticing some tribes, remotely perhaps allied to the true worms, but which only now come within the plan originally laid down for our guidance.
Rudolph confines himself to the proper parasites of animal bodies (Entozoa), which, following Zecler and Goeze, he divides into five orders: 1. Nematoidae; 2. Acanthocephala; 3. Trematoda; 4. Cestoidae; and, 5. Cystica. In our exposition of their characters and genera, we shall reverse Rudolph's plan, and begin with those of simplest organization.
Order I.—Cystica.
Character.—Body flattened or roundish, continued posteriorly into a vesicle peculiar to one or common to several individuals. Head furnished with two or four bothria, or with four suckers, and a circle of hooked prickles, or with four prickle-boscidiae.
Genus Echinococcus.—An external simple or double vesicle, to the inner surface of which many entozoa adhere, like grains of sand. Of these the body is obovate, and the head armed with a circle of hooked prickles and suckers. The species infest the viscera of man, of apes, and of domestic cattle.
Genus Cestocerus.—Vesicle simple, containing many adherent entozoa. Of these the body is elongate and flatish, rugose; the head armed with a prickle-beak, and with four suckers. The only known species (C. cerebralis, Plate VI. fig. 8) is found in the brain of domestic animals, especially of sheep, and it is the cause of a disease in them known by the name of the hardy. It is curable by the judicious use of the trephine.
Genus Cysticercus.—Plate VI. fig. 7.—External vesicle simple, containing a solitary entozoon, whose roundish or depressed body passes insensibly into a caudal vesicle. Head furnished with four suckers and a prickle beak. The species are found in quadrupeds, principally in their abdominal viscera. One occasionally makes good its habitat in the cellular substance between the muscles, and even in the eye and brain of man; and the same is very common in the muscles of swine, whose flesh is then said to be encased. Blumenbach, as we have before mentioned, asserts that the wild swine are not subject to this disease; but the assertion seems unfounded. "In suis domestici cerebro et omnibus partibus musculosis valgitudinis occurrit, neque fere deest." Rud. Est. Syn., p. 189, c. p. 547.
Genus Anthocephalus.—External vesicle hard and elastic, containing a more delicate one, within which there is a solitary
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1 Entozoon Synopsis, &c., Berlin, 1819, 8vo. 2 Bothria are small pits or excavations, with a thickened rim, placed round or near the mouth. 3 On this order the reader will consult with advantage Dr Hodgkin's Lectures on Morbid Anatomy, vol. i. pp. 184-197. 4 On this genus see some interesting observations by Dr Drummond in the Magazine of Natural History, n.s., vol. ii. p. 655, &c., and vol. iii. p. 227. intestinal former circle of them; nay, he believes that he has even seen the remains of suckers in these vesicles. Still, however, there remains much obscurity on this strange transmutation; and even a greater darkness covers the origin and the propagation of the maternal vesicle. Since the *Echinococcus hominis* frequently presents us with small hydroids enclosed within each other after the manner of a nest of pill-boxes, we are forced to believe that the exterior hydroid is the primordial vesicle, within which the others have been successively evolved; but how? "I can no more answer this question," says Siebold, "than I can account for the existence of the primordial vesicle itself."
**Order 2.—Cestoidea.**
**Character.**—Body elongate, flattened, soft, continuous, or jointed. Head very rarely simply hipped, usually furnished with two or four bothria or suckers. Androgynous.
**Genus Tenia.**—Body elongate, flattened, jointed. Head with four suckers. The Tenia inhabit the alimentary canal, and principally the small intestines, but they have been found very rarely in the liver and gall-bladder. They occur only in vertebrated animals, some of them nourishing two or three species. In those species which Rudolph has described without any work of doubt to their reality, we find that these insects may, thirty-two in mammals, sixty-three in birds, six in fishes, and two reptiles. These parasitic species he divides into two sections: first, those with an unarmed, and, secondly, those with a pricked head; but Mehlis has recently shown that many species which are furnished with hooked prickles when young, lose them when they arrive at maturity.
**Genus Bothriocephalus.**—Body elongate, flattened, jointed. Head subtetragonal, with two or four opposed bothria. Nearly allied to Tenia. Of twenty-four species described by Rudolph, one is peculiar to man, three to aquatic birds, and twenty to fishes. The genus has been subdivided into several others by De Blainville. The individuals of one of these subgenera, *Dibothriacanthus*, were affixed by the prickles of their proboscis to masses of Ascarides, which again were adhering to butter-fish.
**Genus Ligula.**—Body elongate, flattened, subarticulated. Mouth two-lipped, armed on each side with two tricuspidate spines. There is but one species, a native both of fresh and salt water fishes.
**Genus Tetrahyphalus.**—Plate VI., fig. 6. Body flattened, unjointed. Head furnished with two bipartite bothria, and protruding four retractile prickly proboscides. The species are all piscivorous, although one has been also found in the stomach of a tortoise, and another in some cuttle-fish. They adhere to the abdominal viscera, to the gills and fins, and even infest the muscles. Bremer is of opinion that the species are Bothriocephali in an imperfect stage of development; and Nordmann believes this opinion to be correct, at least in regard to certain species. On the genus see Drummmond in *Mag. Nat. Hist.*, n.s., vol. ii., p. 571, &c.; and Leblond in *Ann. des Sc. Nat.*, n.s., tome vi., p. 283. The latter took a species from the interior of a fluke-worm or Distoma, a true entozoon, the parasite of another of not superior organization, and scarcely of greater bulk. Helminthology is indeed full of miracles.
**Genus Gynocephalus.**—Body flattened, unjointed, very long, with a subglobular receptacle for the neck. Head furnished with two bipartite bothria, and emitting four naked retractile proboscides. Found immersed in the flesh of some gilthead (Brama), and rays or skates (Raja).
**Genus Scolex.**—Body flattened, unjointed. Head furnished with four bothria. The only species described (*S. polymorphus*) is common in the intestines of many fish and of the Cephalopods. There exists a suspicion that other Scoleces may be metamorphosed into Bothriocephali.
**Genus Caryophyllaeus.**—Body flattened, unjointed. Head enlarged, scalloped, two-lipped, the lips superior and inferior. The species is common in the intestines of the carps (*Cyprinorum*).
In the preceding order there were no appropriated organs of digestion, which begin now to be developed. In the majority of the Tenia there are two or four canals which run through all the articulations of the long tape-like body, and which, underneath the cephalic knob, are connected together by numerous anastomoses, forming there a sort of network. It is remarkable that no one yet has succeeded in proving any direct communication to exist between these canals and the proboscis. In all the Tenia, the Bothriocephali, the Schistocephalus, and in the Trienophorus, the generative apparatus, both fecundating and reproductive, is multiplicate, while it is simple in Caryophyllaeus. The orifices of both apparatus are, it seems, always separate. In *Tetrarhynchus epistocyle*, Nordmann did not find any sexual organs; and the four retractile spinigerous proboscides led by four canals to as many oblong, transparent, muscular reservoirs, which, he conjectures, ought consequently to be considered stomachs. In the posterior part of the body of these animals, the same distinguished naturalist discovered a vascular system composed of several longitudinal canals, and ramified by anastomoses; but no movement of any liquid could be perceived in it. On the posterior margin of the body there is a thick fringe of cilia, which is easily detached.
The eggs of the Cestoidea are multiform, and vary remarkably in size. According to Siebold, some have a single envelope, and others not fewer than three. The eggs of *Tenia stylosa*, when found in the intestines of *Coreus glandarius*, are quite peculiar in their structure; for they have four envelopes, of which the two external ones are round, the inner one oval, and that which lies between the second and the fourth is very narrow and drawn crosswise, having at the same time two very long twisted diverticula. The eggs of *Tenia cucumerina* deserve also to be particularised, from ten to twenty of them being always placed in a common envelope. The vesicle of Purkinje appears to be wanting in the eggs of the Cestoidea.
The embryo, while yet in the egg, is endowed with certain motions; and Dujardin discovered that the Tenia have then six hooked spinules, or horny falciform teeth, disposed symmetrically in pairs. These spinules have no relation, as one is at first disposed to conclude, with the spinules that arm the interior of the extrusile proboscis, or the circumference of the oval aperture, for they exist in the embryos of unarmed Tenia, as well as in those which are so provided; nor are the shape and disposition of the two kinds at all analogous.
The articulations of the body are not formed until some time after the embryo has quitted the envelope of the egg, but the first traces of the suckers surrounding the beak are sooner recognisable. It is probable that the little worm from the tench, described under the name of *Gryporhynchus pusillus* by Nordmann, is only the young of one of the Cestoidea, perhaps of a Tenia.
**Order 3.—Trematoda.**
**Character.**—Body flattened or roundish, soft, furnished with succorial pores. Androgynous.
**Genus Monostoma.**—Body soft, roundish, or flattened. The sucker anterior and solitary. The Monostomes live in the abdomen and intestines, and have been found in the muscles, of vertebrated animals. Of the species described in Rudolph's Synopsis, one is from a mammal, nine from birds, ten from fishes, and three from reptiles.
**Genus Amphistoma.**—Body soft, roundish; an anterior and posterior pore or sucker. Of eighteen species, twelve belong to birds, three to the mammalia, and three to reptiles. The genus has been recently subdivided, or its definition will at least embrace the Holostomum of Nitzeck, the Amphistoma and Diplodiscus of Dissing; and the beautiful Diplostomum of Nordmann, found in the eyes of fishes, is nearly related.
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1 See Burdach's *Traité de Physiologie*, vol. iii., pp. 32-34, Paris, 1838. Genus Distoma.—Body soft, flattened, or roundish. Suckers solitary, one anterior, the other ventral. A genus better known by the name of Fasciola. The species are the parasites of every order of vertebrate animals, and are exceedingly numerous, nearly 200 having been described. Of these, the most notorious is the Fluke (Plate VI., fig. 9), generally believed to be the cause of the rot in sheep, by which disease numerous flocks are annually destroyed. Another species (Fasciola trachea, Montagu in Wern. Mem., l. p. 197; pl. 7, fig. 4) breeds in the windpipe of poultry, and produces the fatal distemper usually termed the gapes.
The three preceding genera are the heads of a large family, extremely variable in the degree of organisation, but, amid this diversity, always marked by having from one to three suckers of more or less perfect formation. It is from the number, the form, and the position of these organs that attempts have anew been made to subdivide the family into groups and genera; for many new and extraordinary forms have been discovered since the publication of Rudolph's work. Our space forbids us to characterise these novelties, but we may mention the Gregaria of Dufour, living in groups in the alimentary canal of tardigrade insects; the Diplostomum, which peoples the humours of the eyes of fish; the Cercaria of fluviatile mollusca, so remarkable for its anomalous mode of propagation; and the Diplozoön, the only animal known which is truly double, having two heads and two bodies united at their middle, and in organic connection, and, unlike the Siamese twin, no monstrous production, but a normal species after its kind.
Some of the species in the family are without sex, and seem to be composed of granules lying in a fluid gelatinous matrix, held together by a thin skin, which gives the animal form and consistency. On the contrary, in the greater number of the species there is a digestive apparatus, consisting of a mouth, an oesophagus or pharynx, and an intestine forked or sometimes ramified; but there is no anus, for the ascription of this name to the posterior sucker is founded in error. In several genera we find subservient to the digestive organs a double system of vessels, one closed, the other (furnished with a reservoir, named by some helminthologists the cisterna chyli) has a communication with the exterior by means of a caudal aperture, the vent of some secretion. These more complex species are all hermaphrodites, some fecundating themselves, while others copulate after the fashion of the snail. The sexual organs are often very complicated and much interwoven, but they have distinct orifices. The eggs are diversiform, and usually laid anterior to the formation of the embryo. There are some exceptions, however, and at least one species of Monostoma is viviparous. When the embryo is matured, the upper part of the shell of the egg bursts and opens like an operculum, allowing the embryo to pass out; and then it swims about vivaciously in the circumfluent medium by means of cilia that cover the body. We know not what may be the number and the nature of the metamorphoses through which the young passes before assuming the shape of the parent. The young of the Monostoma mutabile, observed by Siebold, contained all of them a worm of a peculiar figure, having no correspondence with the figure of the mother, but resembling the cyst of some Cercariae. Analogy induces Nordmann to believe that this worm within the young is in fact changed into a cyst, from which, under favouring circumstances, the Monostoma is ultimately developed.
Genus Tristoma.—Capsulae of Bose.—Body flattened; two simple suckers in front and a radiated one behind; the mouth emitting a proboscis between the former. The species infests the gills of various fish. It is occasionally found at freedom in the sea, and has occurred on the British coast.
Genus Pentastoma.—Body roundish or flattened; mouth protruding a little hook, placed between the anterior suckers, of which there are two on each side, arranged in a lunated manner. Parasites of the viscera of the quadrupeds. The best known species is found in the frontal sinus of the dog and of the horse, growing to the length of six inches. The sexes are distinct. The name Linognathus has been preferred for the genus, of which Diesing has published a monograph, with descriptions of eleven species. Because the sexes are separate, Cuvier gives it a place among the Nematoidae, while Diesing thinks its peculiar structure entitles it to be reckoned the type of a separate order, which he names Acantothoraces; and Miram expresses an opinion the same as Diesing's. Recherches sur l'Anatomie du Pentastome Trematode, in Ann. des Sc. Nat., n.s., tome vi. p. 135. (Plate VI. fig. 5.)
Genus Polystoma.—Plate VI. fig. 10, 11.—Body roundish or flattened; six suckers in front, a ventral and posterior one solitary. This genus is the type of a family named Polystomatidae by Blainville. It contains many genera, and among them the Tricota, and others which have been confused with the Leeches. The bulk of the species prefer the exterior of animals, especially the gills of fish, to which they adhere by means of the prehensile organs or suckers on the hinder part of the body. All of them are hemaphroditic. The orifices of the genital organs are in front, not far from the mouth. On each side of this there is an oblong or round sucker; in the oesophagus a body resembling a tongue has been distinguished; the alimentary canal is dendritic, without an anus, and all the body is permeated with a double vascular thread, in which there is obviously a circulation of blood, attended with a vibratile motion. Some species are furnished with eyes, or eye-like specks; and the surface of the body is variegated with spots, or tinctured of a deep colour.
Order 4.—ACANTHOCEPHALA.
Character.—Body roundish, utricular, elastic; proboscis retractile, armed with spinules arranged in rows; sexes separate.
Genus Echinorhynchus.—The only genus of its order, but a very numerous one, for not less than 100 species have been discriminated. They are found in the intestines and other viscera of vertebrate animals, retaining themselves in their position by means of the prickly proboscis, which is not the organ for taking their food, for its extremity is not perforated. The sexual organs are very complex. The ovaries are not attached, but float free in the cavity of the sac-like body. They produce minute spicula, and appear to be discharged posteriorly through a minute pore. It seems that the species undergo a considerable change in figure in their progress from the embryo to the adult state; and some lose the prickles of their proboscis.
Order 5.—NEMATOIDEA.
Character.—Body cylindrical, elastic, the intestinal tube terminated at one end by the mouth, at the other by an anus; sexes separate.
Genus Ligurhynchus.—Body elastic, round; head evulvar; mouth with a smooth protusible tube. Of the three species mentioned in Rudolph, one infects the badger, one the seal, and one the conger eel. Diesing has lately characterised several allied genera.
Genus Orthostoma.—Body round, elastic, attenuated towards each extremity; head with an inferior and superior lip. The Fasula of Lamarck. The species are intestinal, and occur in quadrupeds and fishes occupying the swimming-bladder of the latter.
It is probably in the neighbourhood of Ophistoma that we should place the genus Tetastoma of E. Forbes, a strange parasite, "fixing itself by means of four suckers or mouths to the walls of the stomach, and of the vessels of the Cydippe, after interrupting the circulation of the fluids." Mr Forbes first described it as a tongue-shaped organ existing in the stomach of the crystalline-medusans, but its parasitical nature was discovered by Major Playfair of St Andrews. See Athenæum, Sept. 26, 1840, p. 746.
Genus Ascaris.—Body round, elastic, attenuated at both extremities; head trivalvular: spiculum of the male double. The species are numerous, and difficult of discrimination. The most common example of the genus is A. lumbricoides, found in the small intestines of man, of the swine, of the ox, horse, and ass. See Plate VI. fig. 3.
Genus Strongylus.—Body round, elastic, attenuated at both