Chapter IX: 183 (2)

These vesicles in pork come from the eggs which the tænia has scattered in its passage, and if the pig comes by chance in contact with the fecal matter of a person infested by one of these worms, it is soon infested and becomes what is called measled; in this fecal matter there are either free eggs which have been evacuated by the worm, or else fragments, known long since under the name of cucumerinæ, which are full of eggs.

These fragments of tænia, which I have proposed to name proglottides, and which are nothing else than the worm in all its sexual maturity, are still living and wriggling at the moment of their evacuation, or else they are dead and often completely dried; but in either case, they are full of eggs. Each egg is surrounded by membranes and shells, which effectually protect it against all dangerous contact.

A fragment of the mature tænia, thus filled with eggs, when introduced into the stomach of the pig, is rapidly digested, and the eggs are set at liberty. These lose their shells by the action of the gastric 218 juice, and there issues an embryo singularly armed. As we have before said, it carries in front two stylets in the axis of the body, and on the right and left sides two other stylets curved at the end, which act like fins. These embryos bore into the tissues as the mole burrows into the soil. The middle stylets are pushed forward like the snout of the insectivore, and the two lateral stylets act like the limbs, taking hold of the tissues and forcing the head forwards. In this manner the embryos perforate the walls of the digestive tube.

An egg of the _Tænia solium_ may be swallowed by a man instead of passing into the stomach of the pig. It is hatched in his stomach precisely in the same manner, and the embryo takes up its lodging in some enclosed cavity. Some have been found in the eye-ball, in the lobes of the brain, in the heart, or in the muscles. We have lately read an account of the effects produced by one of these wandering worms, on a man who died after suffering from a peculiar disturbance of the mind. Two spirits seemed to haunt and speak to him, the one a German, the other a Pole. Filthy images were called up before his imagination. At the post-mortem examination, cysticerci were found to occupy the sella turcica, near the commissure of the optic nerves. One of these was alive, the others were calcified. Two others in a similar condition occupied a lobe of the brain.

Man harbours not only the _Tænia solium_, but another species very similar, which naturalists have only learned to distinguish from it during the last few years, the _Tænia medio-canellata_. We give a magnified representation of the scolex, that is to say, of the head of this worm, which has no crown of hooks in the middle of its four 219 suckers.

This solitary worm is introduced by means of beef, and the cysticercus, during its abode in the cow, manifests already the peculiar characteristics which enable us to recognize the species, that is to say, no crown of hooks, but four suckers, and in the middle of them, some blotches of pigment. Leuckart fed a calf with eggs of this tænia, and at the end of seventeen days, the animal died of acute miliary tuberculosis, produced by the great abundance of cysticerci. This second species, which had been always confounded with the preceding, and which is nevertheless the more common, has therefore a different origin from the _Tænia solium_. Observations made quite recently in the north of Africa demonstrate this. Great difficulty had sometimes been felt in explaining the presence of the tænia in persons who had not eaten pork. This embarrassment arose from the confusion of the two species, and this confusion is the more easy as the head of the colony must necessarily be found in order to distinguish them.

Scharlau, at Stettin, found tæniæ in seven children who had been fed, on account of anæmia, with raw meat. The tæniæ were those of this species. We have ourselves found them in children to whom the use of raw meat had been prescribed.

We do not think it necessary to speak here of a third species of tænia (_T. nana_), which also lives at our expense, but which has been 220 hitherto found only in Egypt.

We know perfectly well the itinerary of the _Tænia serrata_ of the dog, which is so abundant, that there are few of these animals that do not enclose some and even many of them. There are few except lapdogs which do not harbour them. We can easily assign the reason. Every tænia, like every animal, has its eggs; each plant has its seeds. These eggs are laid by the mother in the most favourable condition for the development of her progeny. The dog deposits its dung on the grass rather than in any other spot, because the eggs of its tænia, which are destined to the rabbits or hares, will have greater chance of arriving at their destination than if they were exposed on the bare earth, or in the water. Their prodigious number is calculated according to the chances of their arriving safely. The egg, when introduced into the stomach of the rabbit, is rapidly hatched in this organ under the action of the gastric juice, and the embryo which is produced from it seeks its hiding-place in the midst of the tissues which surround it; it bores into them, and establishes itself in the folds of the peritoneum. Then, once in its resting-place, it barricades itself, and waits patiently for an opportunity of introducing itself into the stomach of the dog.

This microscopic embryo is armed with six hooks, like embryos of all the cestodes; it employs them with much dexterity to pierce the walls of the organs, and to hollow out a space for itself in the substance of the tissues. Shut up in its hiding-place, membranes form around for its protection; its six hooks, having become useless, wither; other 221 hooks in the form of a crown appear by the side of four rounded projections, the future suckers; and, sheathed in a large vesicle full of a limpid fluid, it waits patiently for the moment when it will find a place in the stomach of a dog. If good fortune awaits it, it will wake up, some fine day, in the stomach of the animal which has eaten the rabbit, its former home, and a new life will commence for it. The organs in which it was imprisoned are digested, it gets rid of all its swaddling-clothes, unrolls itself, separates from the vesicle which has protected it hitherto, and penetrates into the intestine; there, immersed in the food of its host, it grows with extreme rapidity, and assumes the form of a ribbon or tape. The ends of this tape are successively matured, detach themselves, and become the complete worms, full of eggs, which are evacuated with the feces; scarcely have they made their appearance in the open air before they burst and scatter their eggs.

He whose scientific curiosity is sharpened, has only to watch the dung of the dog at the moment of its evacuation to distinguish on its surface worms of a milky-white colour, contracting like leeches, which are the true _Tænia serrata_ in its adult state. Experiments made on this species have given sanction to what I had said respecting the cestodes.

The tænia, under the name of _Cysticercus cellulosus_, lives in the folds of the peritoneum of the rabbit and the hare, and passes directly from the rabbit to the dog to become complete.

It is very curious that the fox, so nearly allied to the dog in appearance, and which also eats rabbits, never has the _Tænia serrata_, but this animal nourishes other worms.

It was with these cysticerci that I made experiments on four dogs, 222 which I took with me to Paris, in order to convince those who could not believe in the migration of parasites. It was this species that I gave also to the dogs which served as a demonstration at Paris at the course of lectures given by Mons. Lacaze Duthiers.

Some years ago, while making a post-mortem examination, at the Museum of Paris, of some young dogs which I had previously infected with _Tænia serrata_ at Louvain, there were found by the side of these some _Tæniæ cucumerinæ_. These dogs had taken nothing but milk and cysticerci! Whence came these _Tæniæ cucumerinæ_? I knew not, and I frankly owned it to the members of the Commission who proposed the question to me. This however did not prevent my being greatly puzzled with the presence of this worm of whose origin I had no idea. Now we know whence they came. An acaris, the Trichodectes, lives in the hair of young dogs and harbours the scolex of this cestode. The dog, by licking its own hair, grows infested, like the horse, which in a similar manner introduces the gad-fly, and although it has taken no other nourishment, harbours its own epizoaria.

The name of _Cysticercus tenuicollis_ has been given to a vesicular worm which inhabits the peritoneum of the ox, the goat, the sheep, &c., and which turns to a tænia in the digestive tube of the dog. Mons. Baillet has made the principal experiments on this transmigration. The itinerary of another cestode worm, the _Coenurus_ of the sheep, is to pass through the sheep in order to reach the wolf or the dog. This worm has only lately been recognized in its tænoïd form; it has, on the contrary, been long known under the name of _Coenurus cerebralis_; this develops itself on the brain of the 223 sheep, and occasions the disease known by the name of "gid." This disease may be produced artificially. The sheep which swallows the eggs of this tænia shows the first symptoms of it towards the seventeenth day. If we kill it at this time, we find on the surface of the brain, either at the base or the summit, or sometimes between the hemispheres and the cerebellum, one or more white vesicles of the size of a pea, and on which no traces of buds are yet to be seen. This vesicle, of a milky-white colour, and filled with liquid, is the scolex. Near these vesicles are to be seen some very irregular yellow furrows, like tubes abandoned by some tubicolar annelid; this is the gallery through which the vesicular worm has proceeded to the place where it has been found.

A fortnight later, that is to say, about the thirty-second day, the coenurus is as large as a small nut, and one can see with the naked eye some small nebulous corpuscles, separate from each other, of the same form and size; these are the buds or scolices which have risen up, but which, as yet, have neither hooks nor suckers.

We give the representation of one of these vesicles, on the internal walls of which young scolices have been developed; this is nearly of the natural size. Fig. 2, _a_, _a_, shows these scolices of nearly the natural size. Fig. 1 represents an isolated and magnified scolex; 224 A, shows the segments of the future proglottides; D, the suckers; C, the hooks; H, the vesicle which contains them.

Eggs of the same tænia have been given to sheep at Copenhagen and at Giessen, and Messrs. Eschricht and R. Leuckart have obtained the same result as we had at Louvain. On the fifteenth or sixteenth day the first symptoms of "gid" declared themselves. At about the thirty-eighth day the crown of hooks appeared, the suckers were formed, and the whole head of the scolex was sketched out. All these heads can leave or enter the sheath at the will of the animal. It is truly a polycephalous animal when the scolices are expanded. This worm continues to grow for a long time in the cranial cavity, and produces by its presence the gravest results. The sheep necessarily dies at last, unless we remove the parasite by means of the trepan.

The coenurus, at this point of development, swallowed by a dog, undergoes great changes in a few hours. The proscolex, or large vesicle, withers; the different scolices unsheath their cephalic extremity, become free, penetrate into the intestine with the food, and attach themselves to its walls, so as to form as many colonies of tænia as there are distinct heads. A dog which has swallowed a single coenurus may therefore contain a considerable number of tæniæ.

The development of this worm proceeds very rapidly, and it only requires three or four weeks to attain many feet in length. The organization of this worm, in the state of strobila and of proglottis, is in every respect like that of the _Tænia serrata_; we have even endeavoured in vain to distinguish these worms from each other 225 by their hooks. The wolf or the dog follows the flock of sheep, scatters the proglottides or the eggs in their way, and the sheep, browsing on the grass with the eggs attached, become infested with their most dangerous enemy.

To arrest this disease, only one thing is necessary, to destroy by fire the head of every sheep attacked by the "gid." The rest of the animal may be eaten without danger.

Pouchet did not succeed in giving sheep the "gid" at first, for the very simple reason that he employed the eggs of the _Tænia serrata_, instead of those of the _Tænia coenurus_; he had confounded the two species. The coenurus of the sheep is a true calamity when it spreads in a country. The animal attacked by it is lost, and the mischief may be indefinitely propagated by giving as food to dogs the head of the sick animal, with thousands of young tæniæ enclosed within each.

There exists a singular cestode which bears the name of _Echinococcus_. We give a figure of the echinococcus of the pig, slightly magnified, and an isolated scolex (Figs. 55 and 56). In its first form it is composed of closed sacs, which grow to the size of a nut, and sometimes to that of an orange. It usually lodges in the liver of the pig, but establishes itself also in man. We have been assured that part of the population of Iceland have been attacked by it. The abundance of this parasite in that country is attributed to the want of cleanliness, and the number of dogs that they keep around them. The echinococcus becomes a tænia in this animal. It scatters the eggs with its dung, leaving them directly or indirectly on plants which the Icelanders eat; for they gather for food certain mosses, 226 sorrel, cochlearia, dandelion, &c., from the midst of the plains in which live flocks of sheep guarded by dogs. The eggs are scattered everywhere on plants or in the water.

Leuckart has made some very interesting experiments on the echinococci. In Fig. 57 is shown a tænia which proceeds from an echinococcus.

There is yet another tape-worm harboured by man, the _Tænia lata_, better known under the name of Bothriocephalus. We give in Figs. 58, 227 59, and 60 representations of this worm in the state of a colony, also the scolex or head separately, and an egg. Its history is very curious, especially with reference to its geographical distribution. It is only found in Russia, Poland, and Switzerland, and the limits 228 of the places which it inhabits are perfectly defined. Siebold, during his stay at Königsberg, could determine from the nature of the worms, whether the patient who consulted him lived on one side or the other of the Vistula.

A Russian naturalist, Dr. Koch, thoroughly studied this interesting worm and its evolution. He says that this cestode is rare at Moscow, while at St. Petersburg, Riga, or Dorpat it is common. If this be really the case, it must doubtless be attributed to the fact that in one place the inhabitants drink spring water, and in the other water from the river.

A very curious circumstance is the actual rarity of the Bothriocephalus among the inhabitants of the shores of the Lake of Geneva, though formerly it was very common there. This diminution, if we may not call it disappearance, is due to the change which has been made in the construction of water-closets, all of which formerly emptied themselves into the lake, so that the embryos were hatched in the water, and persons were infested by them through drinking it. At present the refuse of the towns is carefully collected for the purpose of manuring the land. This is the result of the advice of Mons. de Candolle, half a century ago; for this naturalist clearly understood how great was the loss to agriculture from the neglect of this fertilizing agent.

The itinerary of this tape-worm is simple. It passes from man to the water under the form of an egg, or of a proglottis; and from the water to man in the shape of a ciliated embryo. In this manner it is introduced with the water that is drunk. The Bothriocephalus, like other cestodes, is free at the commencement and the end of its life: 229 at the beginning, in order to penetrate into its host; at the end, to scatter its eggs.

Messrs. Sommer and Landois published, in 1872, an anatomical description of the sexual organs of the _Bothriocephalus latus_, of such completeness, that it will be long before any one will again take up this subject, which had so much occupied helminthologists ever since the celebrated work of Eschricht. This memoir is illustrated by superb engravings, which represent these organs under every aspect. Dr. Böttcher, of Dorpat, found in the small intestine of a woman, who died of peritonitis, at least a hundred Bothriocephali. They were but slightly developed, though there were some in a sexual state.

The largest tænia, though not the longest, is the _Tænia magna_, from the _Rhinoceros_, described by Marie; it is, no doubt, the same to which the name of _gigantea_ was given by Peters. The learned director of the Museum of Berlin gave me a fine specimen of it eighteen years ago. The generic name of _Plagiotænia_ has been proposed for this worm.

Almost all birds nourish large and beautiful tæniæ, but they must be studied immediately after the death of their host. They often change their form entirely at the end of a few hours.

Woodcocks and snipes always have their intestines stuffed full of tæniæ and the eggs of these worms. Every bird contains them by thousands. Fortunately we cannot be infested with the tænia of the snipe and the woodcock.

Fig. 61 represents the scolex of the _Tænia variabilis_ of the snipe, 230 and Fig. 62, by its side, shows the crown of hooks more highly magnified. We have made these drawings from worms collected from snipes some instants after their death. We close this chapter on the cestodes with the plate (Fig. 63) of a Tetrarhynchus which is usually found in the plaice. The perfect tetrarhynchi, that is to say, those that are adult and sexual, inhabit the intestines of voracious fishes, especially of the squalidæ.

There are other worms which migrate, and even some articulate animals; but their modifications of form are much fewer than in the preceding, and their changes are generally restricted to simple metamorphoses. We will place at the head of this chapter the Linguatulæ, which have so perplexed naturalists.

We sometimes find in the nasal fossæ of the dog and the horse a worm resembling a leech, with a body completely etiolated, which lives there entirely as a parasite, and whose history has only been known 231 for a few years. Chabert discovered the first species of this group in 1787 in the frontal sinus of the horse and the dog. It had been named _Tænia lanceolata_. All naturalists, Cuvier included, placed this animal among intestinal worms, under the name of _Linguatula_ or _Pentastoma_. The latter name had been given to it, because they mistook the hooks for mouths.

We have shown, from the embryos, in 1848, that the Linguatulæ, instead of being worms, are articulate animals, more allied to the lerneans or acaridæ than to the helmintha. These observations, though received at first with much hesitation, were fully confirmed afterwards, especially by the learned researches of Leuckart. The linguatulæ have a very long body, sometimes rounded, in other cases compressed, with a mouth surrounded by four strong hooks, regularly disposed in a semicircle. They have often been found in the lungs of serpents, in certain birds, and in many mammals. A linguatula was also seen by Bilharz at Cairo, in the liver of a negro, and they have been observed in the hospitals of Dresden and Vienna.

It is to be presumed that this dreadful parasite has been introduced into man by means of the flesh of the goat, and perhaps of the rabbit. Linguatulæ are found in their primary agamous form, in open cavities like the nasal fossæ. Leuckart was the first to show that the linguatulæ, which lived at first encysted in the peritoneum of the rabbit, completed their evolution and became perfect in the nasal fossæ of the dog. The _Linguatula serrata_ (Fig. 65), which lives primarily in the goat, the guinea-pig, the hare, the rabbit, &c., 232 is found accidentally in man, and perfect in certain mammals. Examples have been given of sick persons being completely cured by the evacuation of worms from the nostrils; these worms were, doubtless, linguatulæ. Fulvius Angelianus and Vincentius Alsarius speak of a young man who had suffered for a long time from head-ache, and who passed a worm from his nostrils. It was as long as the middle finger. There is little doubt that this was the _Linguatula tænioïdes_. These parasites may perhaps sometimes lose their way in their peregrinations. Some years ago a lioness died of peritonitis at Schönbrunn, and, after death, the liver, the spleen, and other organs were found to be filled with encysted linguatulæ.

The nematode worms are long and rounded, like the ordinary ascarides of infants, which take up their abode in all the organs of animals of the various classes of the animal kingdom. About a thousand varieties are known, varying in length from a few millimètres to forty or 233 fifty centimètres.

They are not all parasites, as has been thought, since some are found in the sea, and others in damp earth, in putrid matter, and even on plants and their seeds. The migrations of nematodes are subjects of great interest. Their changes of form are usually not very considerable; but the modifications in their sexual apparatus, whether in the same individual, or in the succeeding generations, are very curious.

When we consider the numerous encysted and agamous nematodes, which are found in the different orders of mammalia, birds, reptiles, batrachians, and fishes, there is little doubt that all these beings are only migratory parasites, which pass together with their hosts into the animal to which they are destined. They are found, like ascarides, in animals of all classes. Some are to be met with in all the organs--the brain, the eye, the muscles, the heart, the lungs, the tracheal artery, the frontal sinus, the digestive tube, the skin, and even in the blood. Sometimes the two sexes live under the same conditions; sometimes the male is dependent on its female, or else one generation is parasitical, and the next is independent. There is a great diversity with respect to development. Some nematodes, like trichinæ, are developed so rapidly, that the embryos are already perfect in the egg before it has quitted its mother. Others, like the ascarides lumbricoides, lay eggs, in which the embryos do not appear till several weeks or many months after they have been laid. Between these two extremes we find all the intermediate degrees.

Diezing, who has done more for systematic helminthology than any 234 other naturalist, brought together, under the name of _Agamonema_, all the migratory agamous nematodes which wait for the opportunity of entering their final host. Diezing had kept himself quite independent of the discussion by fixing his attention exclusively on form, without taking account of migration and digenesis. One of these agamonemata, lodged in the midst of a pediculated cyst on the vagina of a bat (the little horse-shoe), was probably a worm that has lost its way; if not, we must admit that these mammals become the prey of some carnivorous animal. But what carnivore can habitually feed on the cheiroptera? There are but few fishes, either in fresh or salt water, which do not enclose in the folds of their peritoneum, especially round the liver, cysts full of these agamonemata.

We see in some of the nematodes examples of migration which are quite peculiar to them. Some of these worms are always free, others free at one part of their life only, others migrate from one animal to another; others again from one organ to another. The _Ascaris nigro-venosa_ of the frog lives sometimes in the lungs, at others in the rectum or quite out of the body in damp earth. The _Filaria attenuata_ lives in the rook (_Corvus frugilegus_), and it is said that it becomes sexual in the intestines of the same bird.

These worms are usually very tenacious of life; many of them can, it is said, be dried for weeks, months, or years together, and return to life as soon as their organs are moistened. Their eggs resist even the action of alcohol and the most active chemical agents, and eggs that had been prepared for the microscope, and had served for many years 235 the purposes of study, have been known to produce young ones as if they had been just laid.

_Natura non facit saltus_ is especially true as to the division of sexes among the nematodes. Between the true hermaphrodites and the true dioecious worms are found species in which the males gradually dwindle and become dependent on the female; this is to be seen in the _Sphoerulariæ_, among which the male is only an appendage to the female sex. We find here full evidence of the fact that the female is more important than the male, with regard to the preservation of the species. In some species the sexes differ but little, in others, the sexual differences become greater, and the male is only one third of the length of the female; but in some of them the disproportion is greater still. At the same time, we see nematodes whose males are attached to the females, so as only to form a single individual; in other cases, the male seems to disappear to such an extent, that we find nothing but the male organ in the female; indeed, there are instances of male worms, which, without changing their form, occupy the cavity of the matrix and, like the lernean crustaceans, are parasites of their females. The _Trichosomum crassicauda_ is an instance of this kind.

Arrangements which would not have been suspected beforehand, are every day revealed, with respect to the conservation of species. We have recently learned from the works of Messrs. Malmgren and Ehlers, and later still, from those of Claparède, that in the same species we may find different males, producing different offspring. Messrs. Malmgren and Ehlers have opened this question by their persevering researches, 236 and Mons. Claparède expected to invalidate the results obtained by them by establishing himself at Naples, in order to devote himself to a new series of investigations. Contrary to his expectations, he arrived at the same conclusions, and announced that a nereid possesses, in one and the same species, two kinds of males and two sorts of females, and that these males differ from each other, not only in their manner of life but in their age, in the mode of formation of the spermatozoïds as well as in the form; that the females differ no less from each other than the males, and that each form is intended to provide, in its own manner, for the dissemination of the eggs.

We see this realized in annelid worms known by the name of _Heteronereidæ_. Certain individuals of small size live on the surface of the water; others, evidently much larger, live at the bottom of the sea and behave quite differently. The eggs and the spermatozoïds proceeding from these two forms differ sensibly from one another, and the difference of form corresponds with that of origin.

We see thus among some of them different males; among others different females: then eggs and spermatozoïds equally different in one and the same animal species.

A curious insect, the _Termes lucifuga_, appears also to distinguish itself by two sorts of males and females, which even take to flight at different periods. Great sagacity was required to reveal these strange facts. Mons. Lespes has had the courage to devote himself to these observations.

We see that all means are good that are for the preservation of the 237 species, but who would have suspected that in a single animal there would be found two males by the side of two females, neither of which resembles the other, and besides these, two kind of eggs and spermatozoïds! How great would be our astonishment were we to see two sorts of cocks, two kinds of hens, and two sorts of eggs produced by the same mother, and hatched at the same time!

Professor Ercolani bred in damp earth certain parasitical nematodes, kept them alive, saw them reproduce, and was even able to obtain several generations of them. These nematodes were the _Strongylus filaria_ from the lungs of the goat, the _Strongylus armatus_ from the intestines of the horse, the _Ascaris inflexa_, and the _Ascaris vesicularis_ from the fowl, and the _Oxyuris incurvata_ from the horse. The first three, whether they are born in damp earth, or in the midst of organs in which they habitually lodge, have the same external characters; nothing is remarked in them except a greater activity in their reproduction.

The _Strongylus armatus_, when born at liberty, appears no longer to have hooks at the mouth like those worms which live in the intestines. Mons. Ercolani has also remarked that these worms, when they become free, are ovo-viviparous, though they were before oviparous.

There are many of these nematodes which are true parasites of man, and although certain of these are as much dreaded as the plague or the cholera, we are far from knowing all their history, and especially the manner in which they are introduced.

A young naturalist, Dr. O. Bütschli, has lately made a good _résumé_ 238 of the state of our present knowledge of parasitical and wandering nematodes.

The Sclerostomata are distinguished by their mouth being surrounded by a horny armature. The river perch usually gives lodging to a viviparous nematode, the _Cucullanus elegans_, on the development of which a special work has been published. The young ones are provided with a perforating stylet, and penetrate into the bodies of small aquatic crustaceans, called cyclops. When they have obtained entrance into this living lodging, they bore through the walls of the intestines and shut themselves up in the perigastric cavity. The cyclops being pursued by the young perch, are swallowed with their guest, and the latter is set free in the midst of the stomach, where it passes through its sexual evolution.

Leuckart saw in his aquarium young Cucullani penetrate into the bodies of the cyclops. These crustaceans are therefore the vehicle of these nematodes. Another nematode worm, the _Dochmius trigonocephalus_, lives at liberty while young, but seeks for an asylum in the dog in its old age. The _Sclerostomum equinum_ causes aneurisms in the horse, which manifest themselves by colic. A hundred of these worms have been found in the same horse. The _Sclerostomum pinguicola_ is very common in the pig in the United States. This is the _Stephanurus dentatus_ of Diezing, noticed by Natterer in Chinese pigs in Brazil. Cobbold notices the same worm as living in the pig in Australia; they have been also found in Germany.

The _Strongyli_ are round, cylindrical worms, with bodies sometimes entirely red, which inhabit different organs in mammals and birds. 239 A very remarkable species, the _Strongylus gigas_ (Fig. 66), exists in the kidneys of the horse and the dog, and sometimes in man. It partly destroys this organ, and has been seen a mètre in length. The _Strongylus commutatus_ often lives in great abundance in the lungs of the hare, and the _Strongylus filaria_ in the lungs of the sheep, occasionally in such great numbers that their presence produces pneumonia.

Porpoises generally have strongyli in their lungs and their bronchia, and they are seen by thousands in the sinus of the Eustachian tube. 240 We collected a large bottle full from a single porpoise around its internal ear. When we consider the prodigious number of these creatures, may we not suppose that they are able to multiply in the organs which they occupy, as well as migrate to infest other individuals.

Different generic and specific names have been given to these Strongyli. A round worm found in the intestines of the dog, the _Strongylus trigonocephalus_, lives at first in damp earth or mud like the rhabdites in general; it then passes into the dog, and there becomes a sexual Strongylus. It is possible that there are others in the same category.

The _Ascaris lumbricoides_ is a large round worm which attains the size of a quill pen, and which is commonly found in the stomach or the lesser intestines of children when in good health. Aristotle was acquainted with it. It has been observed throughout Europe, in Central Africa, in Brazil, and Australia. The same species lives in the intestines of the pig; but the _Ascaris megalocephalus_, which is usually found in the horse, is of a different species.

The _Ascaris acus_ of the pike lives at first in a common white 241 fish, the _Leuciscus alburnus_, and passes with this fish, which serves it as a vehicle, into its final host.

Another common nematode, the _Oxyurus vermicularis_ (Fig. 69), a parasite of man, is a small worm of the size of a fine pin, which often multiplies in the rectum of children, causing intolerable itching. It is by means of their microscopic eggs that they penetrate into the system; these are hatched in the stomach, and are completely developed at the end of eight or ten days. They pass from the anus in great numbers.

The brood of worms from the eggs of the _Ascaris megalocephala_ of the horse live in freedom, and go through all their phases until their sexual development separately; there are males and females. The generation which descends from these is distinguished by being of a 242 much smaller size.

The name of _Trichocephalus_ has been given to nematodes which have the cephalic extremity very thin, and ending in such a fine point that it is difficult to discover the mouth. The Trichocephalus of man (Fig. 68) is a curious nematode, which was discovered by a student at Göttingen, in 1761. It is usually found in the cæcum, in which more than a thousand have been met with together. The female is from 40 to 50 millimètres long, the male about 37 millimètres. A female _Trichocephalus affinis_ having laid her eggs in an aquarium, the whole of the contents were introduced into the stomach of a lamb, seven months afterwards, and the walls of its intestines became infested with trichocephali.

No animal at any time has attracted so much attention as that little worm which lives in flesh, rolled up; it is about the size of a millet seed, and was found by chance in the dissecting-room of a London hospital, some forty years ago. The plague and the cholera did not inspire so great fear, and this fright had almost passed from Germany throughout the rest of Europe. We were not among those who wished to take measures at all hazards against the invasion of this worm, since nothing induced us to believe that more trichinæ existed then in Belgium than in ordinary times. These measures would have produced no other effect than uselessly to disturb the minds of the public.

Trichiniasis, which was the name given to the disease caused by these worms, reminds us of tarantism, that is to say, the effects produced by the bite of the tarantula. Mons. Ozanam wrote an interesting work on this subject, in which he said that nervous tarantism existed 243 during two centuries in Europe, as an epidemic malady. According to him, there prevails at present in the province of Tigre, in Abyssinia, a sort of chorea, or endemic musicomania, which has a great analogy with tarantism; it is the "Tigretier." Nothing but music and dancing can have any beneficial effect during the crisis; but these means would evidently be inefficacious in trichiniasis.

The Trichina is a nematode worm, and not an insect, as it was at first called. Let us imagine an extremely slender pin, such as entomologists employ to fasten the smallest insects, rolled upon itself in a spiral form so as to lodge in a cavity hollowed out in the midst of the muscles, in a space not larger than a grain of millet. These trichinæ 244 of the muscles can be discerned by the naked eye. But before we enter on a particular description (and they are now known in their minutest details), let us notice what were the circumstances which led to their attracting so much attention.

It was in 1832; a demonstrator of a course of anatomy at Guy's Hospital in London, Mr. J. Hilton, found in the flesh of a man sixty-six years of age, who died of a cancer, a great number of little white bodies which he took for vesicular worms. The scalpel, during the dissection of the muscles, met with granulations which blunted the edge of the instrument. Astonished to find in the flesh hard corpuscules which the instrument divided with difficulty, he removed some of them, examined them attentively, but, no doubt, he was not sufficiently acquainted with helminthology to understand their true nature. He referred to Professor R. Owen, the celebrated naturalist of the British Museum, who recognized them as new worms, and gave them the name of _Trichina_, because they are as thin as a hair; he added the specific name of _spiralis_ on account of the manner in which they were rolled up in their cyst. _Trichina spiralis_ is therefore the name of this animal.

Some naturalists, at that time, believed that the filaments of the fecundating fluid of the male were parasitical worms, such as are found in other liquids; and these filaments which were designated by the name of spermatozoïds (the animalculæ of the older naturalists), were considered as beings having a certain affinity with trichinæ. The trichinæ were the intermediate state between these filaments of the fecundating fluid and worms properly so called. It is now known with certainty that these filamentary bodies are no more animals than the 245 globules of blood, and that all that was thought to have been observed of their organization was nothing but pure fancy.

The trichinæ, which are now completely known in the minutest details of organization and manner of life, have a distinct mouth, and they have a complete digestive tube with an orifice at each end of the body, like all worms in the form of a thread, which, for this reason, are called by naturalists _Nematodes_ as opposed to _Cestodes_ (in the form of a ribbon or tape). Besides this nutritive apparatus, trichinæ, like nematodes in general, have the sexes divided into two distinct individuals, so that there are males and females, which can be easily distinguished from each other by the size and form of the body.

Trichinæ are found in the flesh of almost all the mammals. If we eat this trichinous flesh, the worms become free in the stomach as digestion goes on, and they are developed with extreme rapidity. Each female lays a prodigious number of eggs; from each of these comes a microscopic worm, which bores through the walls of the stomach or the intestines, and thousands of trichinæ lodge themselves in the flesh, where they hide till they are again introduced into another stomach. When the number is great, their presence may cause disorders or even death. Leuckart's experiments on animals aroused the attention of physicians, and then it was found that patients who had shewn exceptional symptoms, had fallen victims to the invasion of these parasites. Leuckart counted 700,000 trichinæ in a pound of the flesh of a man, and Zeuker speaks of even five millions found in a similar 246 quantity of human flesh.

The _Trichina spiralis_ produces about a hundred young worms at the end of a week (viviparous); and a pig which had swallowed a pound of flesh (5,000,000 trichinæ) might contain after some days 250 millions, reckoning that only half the worms hatched were females, which is not the case, for there are more females than males. It appears that trichinæ can become sexual in all warm-blooded animals, but the number in which they can become encysted is not so great. It appears that they are not encysted in birds.

In the month of December, 1863, R. Leuckart wrote to me from Giessen; "The Trichinæ are playing a great part at present in Germany (with the exception of Schleswig-Holstein). Two epidemics have made their appearance within a few months, and have produced a veritable panic, so that no person will any longer eat pork. The authorities everywhere are obliged to subject the flesh of these animals to microscopic examination."

We owe to Leuckart (1856 and 1857) and to Virchow (1858) the knowledge of the principal facts of the history of these worms. Virchow ascertained by experiment that they become sexual in the alimentary canals at the end of three days; and these two naturalists discovered, after many researches, that trichinæ are neither strongyli nor trichocephali, but a different kind of nematode, which are hatched in the stomach of those whom they infest, and that their embryos, instead of migrating, establish themselves in the host himself. The embryos of parasites do not usually remain in the animal which gives them lodging; they are evacuated, as well as the eggs, and are conveyed 247 to another animal. The trichinæ are sexually developed in the same animal in which they have been engendered.

Worms which produce eggs do not usually hatch them in the same animal; they are evacuated with the feces. The trichinæ are an exception. These agamous worms, when introduced into the stomach, rapidly pass through their evolutions there, become sexual, lay eggs, and the germs which are produced from them pierce the tissues, and become encysted in the muscles or other closed organs. It appears that the _Ollulanus tricuspis_, a nematode of the cat, presents the same phenomena. It is a species of trichina, which lives at first in the muscles of the mouse which serves it as a vehicle, then in the stomach of the cat, where it becomes sexual and complete.

The _Spiroptera obtusa_ is a worm remarkable for its peregrinations. It passes with the excrements of the mouse into the larva of _Tenebrio molitor_, which is very fond of it. At the end of a month it is encysted in this insect, and after five or six weeks it becomes sexual in the mouse. The _Spiroptera obtusa_ of the mouse lays eggs which are evacuated with the feces; and these become, with the eggs which they enclose, the prey of meal worms, the larvæ of the _Tenebrio molitor_, a coleopterous insect. These germs come forth in the intestine of the larva, they perforate the intestine and become encysted in the folds of fat which surround it. Some fine day the insect is swallowed by the mouse, and the Spiroptera, set at liberty in the intestine, will be gradually matured until its sexual development is complete.

The ordinary crab of our coasts, _Carcinus mænas_, is the vehicle 248 of a nematode which becomes a _Coronilla robusta_ in the stomach of a ray.

The _Heteroura androphora_ is another nematode which lives in the stomach of tritons. The male is always rolled round the body of its female. The two sexes are always free, contrary to that which is observed in the syngami. The Blattæ, coleopterous insects, also harbour sexual nematodes. Radkewisch saw two species of anguillulæ, the _Anguillula macroura_ and _appendiculata_, in the _Blatta orientalis_, and an _Oxyuris brachyura_ in the _Blatta germanica_. These eggs leave the body with the feces, and resist the action of deleterious agents.

_Heterodera Schachtii_ is the name given to a nematode which Mons. Schacht discovered on beet-root. This is also a dimorphous worm; the male has the usual form, the female resembles a lemon. The _Leptodera appendiculata_ inhabits the foot of the _Arion empiricorum_, in the larva state, and becomes sexual (male and female) in the decomposed body of the snail. The next generation has the sexes united, and lives in damp earth. The _Leptodera pellio_ lives in the same way in the bodies of lumbrici; another Leptodera inhabits the intestine of the snail, and a third the salivary glands. The nematode so generally known under the name of _Ascaris nigro-venosa_ also belongs to this genus. It lives in the lungs of the frog. There is one also in the lungs of the toad, but it differs from the preceding.

Leuckart looks upon these worms as females, and their reproduction as parthenogenetic. Schneider considers that the male exists by the side of the female sex, and that they are consequently hermaphrodites. These worms in the lungs are viviparous, and embryos are found in 249 the midst of the intestine of the same animal which gives lodging to the female. These same worms, proceeding from an hermaphrodite parent, or from parthogenetic females, live at liberty, and not parasitically in damp earth or in a decomposed body, and differ from their parents in size as well as in sexual organs. They all become either male or female, and consequently their fecundity is dependent upon copulation. Their parents could all multiply without it, but they cannot. The females alone produce a new generation.

A worm known by the name of _Vibrio anguillula_ lives in grains of corn while still green, and multiplies there to a prodigious extent; it is this which causes the disease known by the name of smut. The grains grow hard, and enclose nothing but little dried worms, which remain thus without apparent life, yet without dying, until they are moistened, when they become damp, the tissues swell, the organs resume their natural appearance, and the functions are restored at the end of a few hours.

In a grain of corn affected by smut, anguillulæ without distinct organs are found, which may be dried and revived eighteen times in succession, according to Mons. Duvaine, who thinks that these anguillulæ, leaving an infected grain, come out of their envelopes in a field of corn, cling to the young stalks, and rise with them. They begin to develop themselves in the rudimentary flower of the corn, and acquire genital organs like nematodes. Males and females are always found separately in a grain of corn.

The ermine lodges in its lungs and tracheal artery a long worm, to 250 which I have given the name of _Filaroides mustelarum_. It usually forms a little sac, which resembles a tubercle. Many individuals of different sexes, wound round each other, are so closely tied together that they can with difficulty be separated. They resemble a ball of cotton. This filaroid sometimes gets into the frontal sinus, and mechanically destroys a part of its osseous walls, so that the skull is pierced by a hole above the frontal sinus. Dr. Weyenberg made this observation.

It is probable that other species of Mustela will present the same phenomena, for the skulls of this animal are often to be found perforated above the orbital cavity.

The _Ollulanus tricuspis_ is a worm which lives in the walls of the stomach of cats; it is viviparous, and the young ones sometimes wander into the muscles of their host. But the natural course of things is that the young are evacuated with the feces, and that these dejecta, according to all probability, form part of the food of mice, and pass with them into the cat. It is to be hoped that Leuckart will soon put this migration out of doubt by a decisive experiment, and will prove that the mouse serves as a vehicle for three different worms, the _Cysticercus_, the _Spiroptera obtusa_, and the _Ollulanus tricuspis_.

Many nematodes lodge in the substance of the walls of the gizzard of birds. In the large goosander we have found one which has round its head four blades, crossing each other, toothed on the concave side. We have given the name of _Ascaracantha tenuis_ to this worm. It has very small eggs. The _Trichosomum crassicauda_ is a nematode of the 251 rat; the female is 2·5 millimètres in length, and the male ·17 millimètres, and it lives in the uterus of its female. Five males are occasionally found in one female. This observation made by Leuckart has been confirmed by Bütschli. The male has its digestive tube incomplete; its female feeds for it.

The bat of the high mountains of Bavaria, known under the name of _Vespertilio mystacinus_, harbours a nematode, the _Rictularia plagiostoma_, the same which is found in Egypt in the hedgehog (_Erinaceus auritus_). The bat on the banks of the Rhine has not this remarkable worm. We must therefore conclude that the bat of Bavaria finds and eats the same insect as the hedgehog in Egypt, and that this insect does not live on the banks of the Rhine. We have never met with this nematode in the mystacines of Belgium, and yet we have opened them by hundreds.

A bird found in Florida, the Anhinga, has in its brain a nematode whose presence in that organ is not accidental.

The _Echinorhynchi_ form a very remarkable group of parasites. They migrate from one host to another; but the vehicle by which the greater part of them is conveyed is not known. We represent in Fig. 72 a species which is very common in the intestine of the sprat.

It is known that these worms migrate when young, and undergo metamorphoses when they change their host. The _Asellus aquaticus_ of fresh water, harbours besides other worms, the _Echinorhynchus hoeruca_; the _Gammarus pulex_, another fresh-water crustacean, lodges the larva of the _Echinorhynchus proteus_ (Fig. 72). We commonly find this beautiful species of the Echinorhynchus in the alimentary cavity 252 of the sprat, and it is easily distinguished by its peculiar form and its orange colour.

The _Asellus aquaticus_ seems also to serve as the vehicle of the _Echinorhynchus angustatus_. The hooks of the embryos differ from those of the adults, as the six hooks of the cestodes differ from the crown of the adults. Leuckart has described those of the envelope of the _Echinorhynchus proteus_ and the _Echinorhynchus angustatus_. The embryo of the Echinorhynchus has only two large hooks on each side, but several smaller ones. The two species mentioned above have on each side five or six hooks placed at right angles with the median line, but they are not all of the same size.

The animals are allied to the _Gordii_ in their development. In fact, their development is like that of the echinodermata; the larva is the _Pluteus_, in which the true echinorhynchus develops itself, borrowing the skin of the pluteus. According to the experiments made by Schneider, the larvæ of cockchafers must be the vehicles of the 253 _Echinorhynchus gigas_. Pigs disseminate the eggs, and the embryos infest these larvæ, in the bodies of which they pass through their principal changes.

The _Gregarinæ_ are microscopic beings, with an extremely simple organization, the nature and the genealogy of which have only lately been known. They live at first encysted by thousands together, under the name of _Psorospermiæ_; they are afterwards hatched in the form of _Amoebæ_, and then transformed into Gregarinæ. They migrate from one animal to another, or from one organ to another, to settle in the intestine, where they assume their adult form. In this state they are monocellular, and do not at any time possess organs which resemble the sexual organs of other classes. The disease of silk worms, known by the name of "pebrine," has been attributed to the development of psorospermiæ.

We give the representation (Fig. 74) of gregarinæ which we have found abundantly on the Nemertes; and (Fig. 75) a peculiar species which lives in the larva of an agrion.

We also give a sketch (Fig. 76) of some very remarkable parasites, 254 whose affinities are still problematical, and which only inhabit spongy bodies, such as the kidneys of cephalopods. The name of _Dicyema_ has been given to them.

Prof. Ray Lankester has quite recently made some very interesting observations, at Naples, on these problematical beings; and my son has just devoted a part of his vacation, with two of his pupils, to elucidate the points of their organization and development, which are still obscure. He went to reside at Villefranche, near Nice, in order to obtain fresh cephalopods every day. His observations have led him to a result quite different from that which I expected.