a division of the terraqueous globe with re- spect to the different degrees of heat found in its differ- ent parts. The zones are denominated torrid, frigid, and temperate. The torrid zone is a band surrounding the teraqueous globe, and terminated by the two tropics. Its breadth is 46° 58'. The equator, running through the middle of it, divides it into two equal parts, each contain- ing 23° 29'. The ancients imagined the torrid zone unin- habitable. The temperate zones are contained between the tropics and the polar circles. The breadth of each is 43° 2'. The frigid zones are segments of the surface of the earth, terminated, one by the antarctic, and the other by the arctic circle. The breadth of each is 46° 58'.
ZOOLOGY is that part of natural history which relates to animals. See Animal Kingdom.
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1 See Du Cange, Glossarium ad Scriptores Medie et Infimae Gracitatis, tom. i. col. 334, voc. Διαγραφή. 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 unsuceptible 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 sea-weeds 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 Acrifa 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 shewn 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 impregnate the whole with sensibility." This property of 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 every thing." 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 shewn 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 excrementious or anal orifice; others have a kind of stomach with only one orifice, which is by turns a mouth and a rent; 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 gemmation, 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, that possesses all things in common, and usually shoots up in an arborescent form.
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1 "Imperfecta veteribus, nec inspe, dicta animantia, destituantur capite, auribus, naso, oculis, pteraque pedibus; ab insectis itaque diversissima, a quibus dudum removi naturae cryptogama."—Lamarck Systema Naturae, 1069. I.—INTESTINAL WORMS.
affords a striking illustration of the wide diffusion of animal life to have ascertained the fact, that almost every species of the vertebrated orders, and very many of the inferior classes, afford, either within or on the surface of the boar, 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 infect 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 (Fasciola hepatica), so common in the liver and gall-ducts 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 Trichocephalus occurs in the ape; the Cysticercus of the cellular tissue is common to him as to 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. Frisch took from a tropical prot an Ascaris, which was apparently identical with a worm that Rudolphi found in our domestic pigeon; and similar examples, more especially 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 birds, nor in amphibia and in fishes; nor, indeed, in the species of any two well-distinguished classes; and so also it is certained 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 verminous. 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 Trichocephalus, 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 Trichocephalus, 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 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, intestinal 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 in nutritive 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 vertebrated animals are verminous, 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. Ascariides prevail to such an extent in Abyssinia, as to regulate in some degree the movements 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 Ascariides are very frequent in the calves of Italy; while those born from the cows of Germany, says Rudolphi, are rarely infested 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 Taenia, 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 Taenia lata, Linn., a species of extreme rarity in the English, Dutch, and Germans, but very common in the natives of Switzerland and
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1 Synonyms: Fasciola; Enteobothria; Vermes; Intestina; Vermes intestinales; Splanchnobothria; Entozoa; Vers intestinaux. 2 Of upwards of 200 species examined by Dr Bellingham, several occurred in six, others in ten, and one in fifteen different animals. 3 Medico-Chirurg. Trans. ii. p. 382. Cyclop. of Anat. and Physiology, ii. p. 124. 4 Ent. Hist. Nat. Hist. part ii. p. 96, 97. 5 Rudolphi considers the Furia an apocryphal animal, but in favour of its existence we have to add to the testimony of Linnaeus and Soeder that of Dr E. D. Clarke. Travels in Scandanavia, part i. p. 208. 6 Paris's Pharmacologia, p. 517. Lond. 1820, 8vo. 7 Lectures on Morbid Anatomy, vol. i. p. 200. Intestinal 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 tumours 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 Rudolph, 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 animacules 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 animacules 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 semeniferi."
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 Linnæus, 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 organized, or has been thrown from organized 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. Rudolph has adopted an opinion very similar to that of Buffon; for it appears to him that 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 develope new organs, until it has acquired in every respect the form and structure and habits of the animal from
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1 Rudolph Eust. Hist. ii. part ii. p. 72, corp. p. 162. 2 Hodgkin's Lectures vol. i. p. 213. On these animated bodies, the reader will find ample information in Blainville's Manuel d'Anatomie. 3 Of various hypotheses of the earlier writers, Le Clerc has given an excellent account in his chapter xiv., "on the origin of Worms in animal bodies." History of Worms, trans. p. 329, &c. where it was separated. Now particles of matter fitted by creation, and their transmission through a living body, for immediate assimilation with it, or flakes of lymph detached from surfaces already organized, seem neither to exceed nor fall below that simplicity of structure which favors 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 favorable 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 favor 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 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. He but from innate workings are we to explain the first origin of worms that have neither sexual 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 Tunicate 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 favored by all causes which tend to disturb the equality between the secreting and absorbent systems. Thus there is 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 unfertilized 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 proboscis (Acanthocephala); the flat or fluke worms (Trematoda); the tape-worms (Cestoidae); and the cystic or hydatid (Cystica). 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 (Planaria) 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 Phanoglene and Enchelidium; and traces of them are visible in the Gyrodactylus auriculatus, in several Cercariae, in the Polystoma integerrimum, in the young of many Distome, 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 oxygenated 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 evolved by respiration in other animals is here furnished.
See an Essay "on the Equivocal Generation of Entozoa," by Dr. Drummond, in the Annales and Magazine of Natural History, vol. i. p. 10-108; and Dr. Good's Study of Medicine, vol. i. p. 292, &c. The argument, as handled by Dr. Drummond, does not satisfy us; and analogies adduced to invalidate the doctrine of equivocal generation by Dr. Good seem far fetched, and some of his alleged facts are not true. The remarks of Andral in favour of their spontaneous origin are strongly stated. See the article "Hydatids" in Cyclop. Pract. Med., vol. ii. p. 440.
Cycticercus cellulare: "The fact of its being found in the swine which man has domesticated, and not in the wild race, appears to furnish arguments of organized bodies which have been formed long after the general creation." Blumenbach's Elem. of Nat. History, trans. p. 243. This fact has been contradicted; but the history of insects and infusory animalculæ furnishes us with many similar, so that the argument is invalidated.
Cyclop. of Pract. Medicine, vol. ii. p. 438.
The reader will find the subject discussed at great length by Rudolph in cap. xviii. of his Historia Nat. Entozoorum, vol. i. p. 370-416. The Phanoglene, which lives in the larva of some neuropterous insects, has some prolongations like antennæ; and Diesing has described new genera (Anycrocanthus, Heterochelidus) with heads furnished with filaments of various forms.
Lamarck's Anim. sans Vert. iii. p. 546, note 1, 2d edit.
Respiratory tracheæ, similar to those of insects, have been ascribed to some of the nematoid worms, but erroneously. See Rudolph's Zoo. Synopsis, p. 579, &c.
M. Chevreul, however, found no oxygen in the gas of either the small or great intestines of three different subjects. See Bostock's Physiology, vol. ii. p. 490.
OL XXI. Intestinal 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 Rudolphi 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 Cestodea 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 Cucullani, as of the oviparous Echinorhynchi, there are found the same bodies which Rudolphi 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 unformed and inconspicuous embryo, or one that is fully formed, but motionless. The ovules of the viviparous species, on the other hand, contain a movable 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 *Tenia 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 *Tenia* 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.
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 Rudolphi'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 *cecum Venerei* of the gelatinous meduse; the Acanthocephala have some ex-
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1 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 mucous present, I have found specimens of a pure white, and others of a bright orange." *Mag. of Nat. Hist.* n. s. ii. p. 519.
2 Rudolphi *Entoz.* Symp., p. 382. See also Owen in *Cycol. of Anat. and Phys.* ii. p. 126, and Drummond in Charlesworth's *Mag. of Nat. Hist.* ii. p. 517-8.
3 *Ann. des Sciences Nat.* n. s. vol. x. p. 34. And so of *Filaria medinensis* Rudolphi writes: "Filariae nostrae prole quasi fætus sunt; quod si barum longitudinem illius vero minuisset spectas, fortunam multa millium militia singulis tribuit."
4 Kirby's *Bridgewater Treatise*, vol. i. p. 331. ORDER I.—CYSTICA.
Character.—Body flattened or roundish, continued posteriorly into vesicle peculiar to one or common to several individuals. Head furnished with two or four bothria, or with four suckers, and circle of hooked prickles, or with four prickly proboscides.
Genus Echinococcus.—An external simple or double vesicle, the inner surface of which many entozoon adhere, like grains of sand. Of these the body is obvate, and the head armed with a ring of hooked prickles and suckers. The species infect the viscera of man, of apes, and of domestic cattle.
Genus Cysticercus.—Vesicle simple, containing many adherent entozoon. Of these the body is elongate and flattish, rugose; the head armed with a prickly beak and with four suckers. The only known species (C. cerebralis, Plate DII. fig. 6) is found in the brain of domestic animals, especially of sheep, and it is the cause of a disease known by the name of the sturdy. It is curable by the judicious use of the trephine.
Genus Cysticercus.—Plate DII. 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 prickly beak. The species are found in the muscles, principally in the abdominal viscera. One occasion makes mention 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 maccad. Blumenbach, as we have before mentioned, thought that the wild swine are not subject to this disease; but the assertion seems unfounded. "In suis domestici cerebro et musculis partibus musculosis vulgatissimus occurrit, neque vero necesse," Rud. Est. Syn. p. 180, c. p. 547.
Genus Anthocephalus.—External vesicle hard and elastic, containing a more delicate one, within which there is a solitary entozoon. Body elongate, depressed, passing into a large caudal vesicle. Head armed with two or four bothria and four prickled proboscides. This genus was previously named Floriceps by Cuvier, and naturalists in general have preferred that designation. The species seem to be almost peculiar to the fishes of southern climates, nestling in the abdominal membranes and viscera.
The Cystica are all gemmiparous. In the Cavernus, the emmae pullulate from every part of the inner surface of the vesicle, where heads and their necks have been found at different stages of development, and always united together in groups. They appear at first like minute tubercles, having the limpidness of glass, and gradually evolve from this formless condition into their perfect state. Siebold has also traced the evolution of the young in the
Echinococcus. The primary or maternal vesicle is lined with an extremely delicate epithelium, to which there adhere some limpid, mostly oblong, corpuscles, analogous to those primary buds met with in the neck of the Caecum. The liquid of the vesicle contains some free Echinococci, within whose bodies, when their coronet of hooks and suckers is everted, nothing more is to be distinguished than some scattered limpid corpuscles. These Echinococci evidently derive their origin from the primary vesicle. On examining the inner surface of it, we notice here and there some minute vesicles, enclosing a mass of delicate granulations, whence the heads of the Echinococci pullulate, either solitary or in groups of from two to seven or more. In fact one portion of the granulous mass forms a small roundish body, which is manifestly continuous with the rest of the mass by one of its extremities. This rounded mass soon acquires insensibly a pear-shape, whence it passes to an oval, while at the same time its attachment to the mass whence it issued becomes more slender and frail. We now begin to discern, in the interior of this body, the circle of hooked prickles and the limpid corpuscles; and now also the heads of the Echinococci commence to protrude and retract these parts, in doing which the entire body is alternately elongated and shortened. Arrived at this stage of development, the thin envelope that enclosed them is torn, but the young Echinococci do not immediately escape, for they are held to its inner surface by a slender cord proceeding from the envelope, and penetrating within their own bodies at a dimple indented in the posterior extremity. This dimple has nearly the appearance of a sphincter muscle grasping this cord of the envelope. After a short period the cords and the Echinococci separate. On being torn up, the envelope of the young Echinococci shrivels upon itself, the Echinococci are ejected, and in this manner they form a rounded mass, in the centre of which the shrivelled envelope is hidden, and upon which the worms repose, as the polypes do upon their stem. These masses sometimes remain for a space hanging from the inner surface of the maternal vesicle, and sometimes they are detached even before the Echinococci have themselves separated. The granulous mass contained in the vesicle is of the nature of a yolk; whence the heads derive the nourishment necessary for their development by means of the slender cords already mentioned. Siebold thinks it doubtful whether all the vesicles, large and small, that contain heads of Echinococci, and which float at freedom in the maternal vesicle among the freed heads, are detached from the inner surface of the vesicle, or whether some of them do not come direct from the freed heads, these having produced germs of Echinococci in their interior, and become distended by them into vesicles. Hanging from the free vesicles containing heads of Echinococci, he has often seen hooked spines, which were perhaps the remains of a 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 hydatids enclosed within each other after the manner of a nest of pill-boxes, we are forced to believe that the exterior hydatid 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 II.—Cestoidea.
Character.—Body elongate, flattened, soft, continuous, or jointed. Head very rarely simply lipped, usually furnished with two or four bothria or suckers. Androgynous.
Genus Ténia.—Body elongate, flattened, jointed. Head with four bothria. The Taeniae inhabit the alimentary canal, and principally the small intestine; 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. Of those species which Rudolph has described without a mark of doubt, as to their reality, we find that one infests man thirty-two, the mammalia, sixty-five the birds, six the fishes, and two the reptiles. These numerous 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 Ténia. 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, Di-bothriorhynchus, were affixed by the prickles of their proboscis to masses of Ascarides, which again were the parasites of a butterfly.
Genus Trienophorus.—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 Ligula.—In its state before evolution the body is flattened, continuous, very long, grooved down the middle with a furrow; and neither head nor genital organs are visible. In its developed state the body is also flattened, unjointed, and very long; the head armed on each side with a very simple bothrium; and ovaries are seen on the medial side, in a single or double series, with threadlike filaments (lemmæ). The species are principally the intestinal parasites of birds; two of three kinds are found in fish; and one has occurred in the common seal.
Genus Tetrahyrnchus.—Plate DII. 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. Bremser 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 Drummund in Mag. Nat. Hist. n.s. vol. ii. p. 571, &c.; and Leblond in Ann. des Sc. Nat. tom. vii. n.s. p. 293. 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. Helmintology is indeed full of miracles. Lib. cit. tom. vii. n.s. p. 249-253.
Genus Gymnophyrmchus.—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 gillhead (Brama) and rays or skates (Rajii).
Genus Scolex.—Body flattened, unjointed. Head furnished with four bothria. The only species described (S. polymerus) 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 (Cyprinidae).
In the preceding order there were no appropriated organs of digestion, which begin now to be developed. In the majority of the Téniae 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 net-work. 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 Téniae, 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 Tetra-
rhynchos epistocotyle, Nordmann did not find any sexual organs; and the four retractile spinigerous proboscides led Wenzel 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 Ténia stylosa, when found in the intestines of Corvus 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 Ténia cucumerina describe also to be particularized, 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 Téniae 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 Téniae, 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 Gryphychus pusillus by Nordmann, is only the young of one of the Cestoidea, perhaps of a Ténia.
ORDER III.—Trematoda.
Character.—Body flattened or roundish, soft, furnished with suctorial 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 Nitzech, the Amphistoma and Diplostoma of Diesing; and the beautiful Diplostomum of Nordmann, found in the eyes of fishes, is nearly related.
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 vertebrated animals, and are exceedingly numerous, nearly 200 having been described. Of these, the most notorious is the Fluke (Plate DII. 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. i. p. 197, pl. 7, fig. 4) breeds in the wind-pipe of poultry, and produces the fatal distemper usually termed the gape.
The three preceding genera are the heads of a large family, extremely variable in the degree of organization, 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