Entozoa (Gr.Entozoa 0600504 within, andEntozoa 0600505animal), a group of invertebrate animals, which during some period of their existence live within and derive nourishment from the bodies of other animals, and with few exceptions belong entirely to the class of helminths or worms. Animal parasites form in fact a sort of sub-fauna, and their number is only to be estimated by the extent of the animal kingdom. The classification of entozoa has been attempted by many eminent zoologists since the days of Rudolphi, who may be considered the father of helminthology; but only recently, and chiefly through the labors of a few observers in. Germany, has it attained the position of a true science. Cuvier refers the entozoa to the class radiata, and subdivides them, following the plan of Rudolphi, into tamioidea or tapeworms, trematoda or flat worms, nematoidea or round worms, and acanthocephala or hooked worms. More correctly, however, they belong to the articulata, though their type is a degraded one, and some of them even approach in structure the mollusca. Adopting this arrangement, wo can best explain the progress and present state of heminthology by considering these subdivisions separately. - Toenioidea, cestoidea, ste-relmintha, tapeworms.

These parasites in their mature state inhabit the intestines of all classes of vertebrate animals. In their transitional state or immature stage they occur as cysts in the tissues and organs of such creatures as form the food of their true bearers or hosts. These cysts, of which the measles in swine are an example, in the early days of science were not looked upon as of an animal nature, and were called hydatids and acephalo-cysts; and not until the latter part of the 17th century was their true character recognized. In the 18th, many observers, and especially Gotze, noticed that their heads closely resembled those of the tapeworms. His observations were confined chiefly to the taeniae of animals, and appear to have had little influence with the scientific men of the next century, who fell back again upon the old and easy theory of spontaneous or equivocal generation; and so it remained until 1844, when Steenstrup's theory of alternation of generation was applied to the problem, and Siebold and Dujardin published essays on the connection between the taeniae and encysted forms of various animals.

Their experiments and those of Kuchenmeister, who must be considered the highest authority on the human helminths, cannot be given in detail here; suffice it to say that tapeworms have been produced in carnivorous animals of all kinds by giving them the encysted forms to eat, and the encysted varieties have been bred in others by administering the eggs or embryos of taenia?. Tapeworms consist of three parts, viz.: head, neck, and colony of joints. The head is a minute object, usually square, and provided with varieties of sucking disks and coronets of hooks, by which it attaches itself to the walls of the intestine. The neck is slender and marked by transverse wrinkles, which gradually are converted into joints. With age these joints increase in number, and finally those first formed become ripe, while new ones are continually given out from the head to supply in turn the place of those discharged. Their growth is generally rapid, and some species attain a length of 100 ft., while others are only a few lines long. Considered as a simple individual, the tapeworm has very limited power of motion, although a distinct layer of muscular fibre is found beneath the skin.

This integument is soft, white, moist, and porous; and through this nutrition is probably carried on by absorption, though the only organs subservient to this function are two pairs of longitudinal canals running along each side of the joints, and united by transverse branches. The skin contains also innumerable roundish, concentrically marked, calcareous corpuscles, recognized only by the microscope, which serve undoubtedly as a sort of skeleton. They possess no nervous system. The sexual organs, however, are remarkably developed. When the oldest joints have become sexually mature (which period varies greatly in different species), they pass off spontaneously by the anus - sometimes by the mouth - of the animal which harbors them. These are flat, quadrangular, yellowish white, and in some species are detached singly, in others by groups. These proglottides, as they are called, are true hermaphrodites, contain the sexual organs and eggs or embryos enclosed within shells, and possess the power of moving about; so that they have often been mistaken for trematoda, and in fact are now considered separate individuals. They discharge their eggs either through the genital opening or by self-destruction, which results either from the bursting of their walls or by decomposition.

They affect chiefly moist places, and, leaving the manure in which they have been deposited, wander about amid the herbage, and may in this way be devoured; or they fall into water, and there bursting, discharge their eggs, which are thus borne far and wide, and find entrance to a proper soil for future development. They are not capable of a long continued independent existence, and may even be destroyed within the intestine of their host, scattering their eggs along this canal, though harmlessly; for Leuckart found by experiment that eggs introduced into the intestine before being subjected to the action of the gastric juice remain unchanged; but that when previously submitted to its influence and then placed within the intestinal canal, the embryos became free. Proglottides may even be swallowed entire by animals which wallow in moist manure, and thus introduce the eggs to their proper dwelling place. When once they have set their offspring free, their object is accomplished and they disappear. Each proglottis contains a vast number of eggs, so that if one out of the many millions reaches a proper habitation the species will not decrease in numbers.

The embryos are enclosed in firm shells constructed to resist a strong pressure from without, and are either brown or yellowish, and round or oval. They probably cannot undergo a great degree of dryness, heat, or cold, or exist very long in fluid, without the destruction of the animal within. The history of the toenia solium, or common tapeworm, will best serve as an example of the usual method of development and transformation of the cestoidea, for it has been most fully studied on account of its frequent occurrence in the form of measles, and its important relation to man. This worm is improperly named, since many are sometimes found in the same intestine. It seldom attains a length of more than 20 ft., and is composed of 600 or TOO joints, which when mature contain myriads of eggs, and escape singly or at once into the outer world. The eggs being set free find their way into water or manure, and are thus scattered far and wide. One occasionally enters the stomach of man on lettuce, fruit, or unwashed vegetables, but more generally they are swallowed by the hog, whose filthy and omnivorous habits need only be considered to show how readily it may become infected.

In either case the egg shell is destroyed by the process of digestion, and the embryo, a minute globular vesicle, armed in front with three pairs of sharp spines, begins its active migrations. It sets out on its travels by boring into the blood or lymph vessels of the stomach or intestine, and is borne along by their currents till it reaches the capillaries, where it renews its activity and bores its way out of the circulatory system into any organ to which chance has carried it. There can be no doubt about this fact, for Leuckart has discovered the embryo several times in the vena portae. It is possible that the embryos may in some cases lose their hooklets in the vessels, and thus, being unable to proceed further, become encysted in the capillaries. Having reached thus a proper situation for higher development, it becomes surrounded by a new formation or cyst resembling the structure of the organ it may inhabit. If it happens to penetrate any serous cavity, this cyst is not formed, but otherwise the development is the same. This process goes on rapidly, so that in a week or two the cyst may be recognized by the naked eye.

The spines or hooklets now drop off, the primary vesicle goes on absorbing nutriment, and by the second or fourth week a protuberance grows out from its internal surface, which soon takes the form of the head of the future taenia. Upon this springs up a double circle of small hairs, which in six weeks become the complete double coronet of hooks. The neck now begins to extend, but the head still remains enclosed in the bladder, till the whole animal is set free. It may continue to live in this encysted stage till it dies of old age, unless set free by nature or art; and this undoubtedly is the fate of the largest portion of these immature creatures. If seated in the muscles, this encysted stage of tapeworm is seldom injurious to man; but if it take up its dwelling place in the brain or eye, which is not unfrequently the case, results most serious follow. In the hog the case is different, for many eggs being devoured at once, the embryos invade nearly every organ of the body, and produce the disease known as measles. We have still to consider the last and highest stage of development in the life of a taenia, viz.: the conversion of these cysts or measles into the mature intestinal worm.

When one of these cysts is accidentally swallowed by man, the little pea-like vesicle bursts, and the head of the worm protruding fastens itself to the intestinal walls by its hooklets. From this head bud out one after another numerous joints, which finally make up the mature worm. It may be easily understood how these small white cysts gain entrance into the stomach of man, for measly pork is often sold in markets, and although thorough cooking and curing destroy the larvae, still the cysts may adhere to the knife, and be thus transferred to vegetables, butter, cheese, and the like, which are eaten uncooked. It may often be the case too that pork is so slightly measly, that the butcher does not know the disease is present. There can be no question about the identity of these two forms, the toenia solium in man and the cysticercus cellu-losoe or measles in swine; for not only are their heads anatomically the same, but it had for a long time been noticed that where measles in pork were abundant, there taenia was of most frequent occurrence, and that where the use of this flesh was forbidden among nations or sects, there tapeworm was scarcely ever found.

All of this led to the belief, especially after the experiments performed in regard to the taenia) and cystic worms of the lower animals, that the measles in meat were the cause of tapeworm in man. To settle this point Kuchen-meister fed a condemned criminal three days before his execution on raw measly pork, and on examination after death the young tapeworms were found attached to the walls of the intestine. One point, however, remained to be proved, viz.: that the eggs of the tapeworm produce the measles in swine. For this purpose experiments were undertaken by the Saxon government under the direction of Ku-chenmeister and other scientific men of Germany. Young and healthy pigs were kept confined separately, and to them were given the eggs of tapeworms. At various intervals they were killed, and the encysted forms were found in myriads throughout the body. These experiments have been often repeated with the same success. To recapitulate: The tapeworm of the human intestine discharges millions of eggs, a single one of which need only reach maturity to produce millions more; therefore it is evident that the vast majority of these eggs perish undeveloped. These eggs must be devoured by some other host to reach their second or encysted stage. This stage is known as measles in swine.

Measles being eaten by man in turn produce the tapeworm. These two forms never produce each other in the same individual.

aenia solium, with different Views of the Head.

Fig. 1. - Taenia solium, with different Views of the Head.

Development of a Cyst.

Fig. 2.- Development of a Cyst.

1. Animal in cyst. 2. Animal with head developed. 3. Head and neck, greatly magnified. 4. Hooklet.

Hooklets of a Cyst, magnified.

Fig. 3. Hooklets of a Cyst, magnified.

Cyst found in Swine.

Fig. 4. Cyst found in Swine.

Various other taeniae infest man in one of their stages, the most dangerous of which is the echinococcus, or encysted form of E. hominis. The cysts produced by this parasite are often as large as a man's head, causing great suffering and death. In Iceland every seventh person is thus afflicted. The explanation lies in the filthy habits of this people, and in the great number of dogs they keep, which assist in spreading the seeds of the disorder. Here the cysts or hydatids contain instead of one scolex or head innumerable embryonic forms, which of course increases the risk of infection. The mature tapeworm produced artificially consists of but three joints, and on this account has hitherto escaped notice. Even now it is not known whether man himself or dogs are the hosts of the mature helminth. Another remarkable species dwelling in the intestinal canal of man is the bothriocephalus latus, or broad tapeworm. This differs from the true taeniae in the construction of its head and joints. The former is oval, flat, and instead of a coronet of hooks and round suckers possesses two longitudinal sucking grooves on each lateral margin, by which it fixes itself; the latter are one third of their width only in length, and the genital opening is found on the middle of each joint, instead of at the lateral margin, as in taeniae proper, and occurs on the same surface throughout its whole length.

They are sometimes as many as 2,000, but even then they do not make up a worm more than 20 ft. long. Thus far this parasite has been found in man only in its mature state. Its geographical distribution is limited to Russia (including Poland), Switzerland, Italy, and the maritime districts of France and north Europe, and it most probably undergoes its transitional stage of development outside the human intestine in some of the iriollusks, which form the food of man. A few other species of tapeworm infest mankind, but they are seldom met with, and will be found enumerated in the accompanying catalogue. The dog, from his domestic and omnivorous habits, is made the host of many of these entozoa, and does much to keep up their precarious existence. Without his aid the toenia camurus would undoubtedly become extinct, and thus the sheep breeders would be rid of a disease which often proves so fatal to their flocks, viz., the staggers. This disease is caused by the presence in the brain of hydatids or cystic camuri, which when eaten by butcher and sheep dogs are converted into the corresponding taenia, the embryos of which are in turn scattered broadcast over the pastures, where they find ready admission to the grazing herds.

This too has been made the subject of searching investigation in Germany, and shepherds are taught to keep their dogs free from this tapeworm, by putting out of their reach the flesh of animals afflicted with the staggers. Sheep may often be kept healthy by keeping them from moist places, and from pastures while the dew is still on the grass, for the proglottides seem to seek such localities, and the heat of the sun appears destructive to their vitality. Much more good may be effected by such preventive measures than by administering anthelmintics, or by attempting the removal of the cysts by the trephine or trochar. Very often immense droves of swine have to be slaughtered on account of the measles, and such attacks always prove that the victims have lately been in the neighborhood of some person who has a toenia solium. Wild swine are never affected in this way. Occasionally this variety of cys-ticercus is found in the flesh of other animals eaten by man, as the ox, deer, and bear, but very seldom. No doubt a great deal of measly pork is sold both fresh and salted, and enough is eaten in an uncooked state in the form of sausages, raw pork, and the like, to account for the wide distribution of taeniae.

Dr. Weinland, in his essay on human cestoidea (Cambridge, 1858), divides the toe-nioidea into two classes: First, the sclerolepi-dota, or hard-shelled tapeworms, the embryos of which, developed in the warm-blooded verte-brata, become mature taeniae only in the intestinal canal of carnivorous mammalia. Thus man obtains the toenia solium from swine; the dog the T. serrata, T. coenurus, and T. echinococcus from the rabbit, the sheep, and the ox respectively; the cat the T. crassicollis from the mouse; and so on. Second, the malacolepidota, or soft-shelled tapeworms, the eggs of which are to be hatched in the stomach of articulata and mollusks. The mature entozoa of this order inhabit the intestinal canal of such animals as prey upon the above, as fish, birds, and insectivorous mammalia. - Trematoda, ste-relmintha (Owen), isolated flat worms. These entozoa are characterized by their flattened, more or less elongated shape, and by ventral sucking disks. The same individual possesses the organs of both sexes. Rudolphi divided them into different genera, according to the number of cup-like suckers present. This classification has been given up, inasmuch as the more important distinctions of structure did not correspond to the external markings; but many of the names have been retained.

Thus the distoma hepaticum, or liver fluke, has two sucking disks. This, the best known of the trematode worms, resembles much a cucumber seed in form, and measures in length one inch, in width about half an inch. It is yellowish brown, probably owing to the bile in which it lives. In this class we first find evidence of an alimentary canal, in addition to the sexual organs, which gives it a higher rank than the cestoi-dea. This consists of a triangular opening or mouth, which may be used either as a sucker or means of obtaining nutriment. From this rises the intestinal canal. An excretory system is also present. This fluke has been found only in a few well authenticated cases in man. Its true home is in the gall ducts of sheep, and it is generally found in the same place in the human system. Cases are on record in which it has been found beneath the skin, having made its way thither by boring into the epidermis. In the liver of the lower animals it works sad havoc in autumn and winter, causing a dilatation and catarrh of the gall ducts, and an interference with the hepatic function, by which, of course, the secretion of the bile is disturbed and changed. They may occur in such quantities as to stop up the cystic duct, and their eggs are deposited in vast numbers in the bile.

The symptoms they create in man need not be stated here. The passage of this worm by the stomach or intestines is the only proof we could have of its presence before death. The generation and development of these worms had been a subject of great interest to naturalists, since Steenstrup made them the object of investigation in illustrating his theory of alternation of generation. The eggs of the distoma, escaping in the form of ciliated embryos, become converted while in the water into nurses or grand-nurses; that is to say, they are not themselves developed into young distomata, but produce in their interior several new organisms, which latter are the real young or larvae of the future animal. These nurses are supplied with organs of self-support. The young brood, known as cercarice, possess in some species tails by which they undertake wanderings on their own account, become attached to mollusks or like animals, and thus find their way into the intestine and liver of some larger animal. The tailless brood have the power of encysting themselves while in the water, and may thus be borne about till they are swallowed by some of the herbivora. This is the general plan of development in all trematode worms, but it is not yet known what peculiar metamorphoses this entozoon undergoes.

There can be little doubt, however, that sheep infect themselves by devouring snails which frequent the grass in moist meadow pastures, or by drinking ditch water. Whether "the rot" is actually caused by this parasite is not absolutely certain, though highly probable, as they are always found in this disease. Little benefit is to be derived from the use of anthelmintics, but a proper attention to these laws of prophylaxis will aid the farmer much in preserving his flocks in a healthy condition. The distoma haematobium forms a very common disease in man in Africa, according to Bilharz, who found it first in the blood of the portal and mesenteric veins. But its chief habitation is the bladder and intestines, and when present in numbers it is very detrimental. In the bladder the worms fasten themselves to the mucous membrane, and produce patches of inflammation, exudation, and haemorrhage. The fungous excrescences thus caused are pedunculated, and often of the size of a pea. Within them the animals may be found, and on their external surface the eggs. In the ureters the inflammation they create is sufficient to produce stricture, and consequent atrophy of the kidney. Several other species of trematode entozoa have been found both in man and herbivorous animals.

Some of them infest the eyes of animals, and are sometimes found in such prodigious quantities as almost to fill the cavity of the eyeball. - Acanthocephala, sterel-mintha, hooked worms. This group of entozoa, which resembles the nematoidea in form and distinction of sex, approaches more nearly the trematoda in its digestive system. It includes some of the most noxious of the parasitic helminths, but none infest man. They are included under one genus, echinorhynchus, which is characterized by its retractile proboscis, armed with recurved spines. It is found in the intestines of the hog and other animals. - Nematoidea, calelmintha (Owen), or round worms. This class is made up of the round worms which inhabit the intestine, lungs, and kidneys of man and the lower animals, or else are enclosed within cysts in the muscular system or beneath the epidermis. They too undertake migrations and undergo transformations, but we are less acquainted with their development than with that of the first two classes; all that we know of them is, that we find sexually mature and embryonic forms, but to trace a connection between them, or to discover their mode of growth, has hitherto been possible only in a few species.

They are distinguished from the cestoidea and trematoda by a more elaborate digestive apparatus, by a nervous system, and by individuality of sex. Most of the species are oviparous, and the development of their eggs has been lately made the study of helminthologists. The ova are enclosed in hard shells, within which under suitable conditions the embryo is further developed by segmentation, till it breaks from its habitation, and comes forth either a perfect worm, or in an intermediate form, in which it wanders into the tissues of man and other animals, where it may undergo the encysted stage, and finally on escaping become the mature individual, when it has found again a suitable habitation. The largest of this class is the strongylus gigas, which belongs to the dog and other animals, but which has been found at rare intervals in the human kidney. It is a long, cylindrical, red monster, with a mouth made up of six papillae. The male, as usual in the nematoidea, is the smaller, measuring from 10 to 12 in., while the female sometimes attains the length of 3 ft., and is half an inch in thickness. This sea serpent of the human entozoa seems really to cause very little trouble.

Like the ascaris, its relative, its fine red color seems owing to a reddish oil secreted by the vaccuoles of the skin. Another species, S. equinus, is very common in the intestine of the horse, and 8. longivaginatus has been found in the lungs and bronchial glands of man. The ascarides are very numerous, and inhabit the intestines of many animals. The ascaris lum-bricoides is the largest which infests the human intestine. It is found all over the world, and prefers the lower part of the small intestine. It is of a pale, pinkish hue, cylindrical and elastic, has pointed extremities, and varies greatly in size according to age and sex. The male measures from 4 to 6, the female from 8 to 18 in. in length. The head is trilobulate with a constriction below the papillae, which serve as sucking surfaces. The intestinal canal is a straight tube piercing the centre of the worm from end to end. They are very prolific, and as many as 64;000,000 ova have been found in one female. These eggs when immature are triangular and very irregular in shape, but when impregnated are enclosed in oval shells, within which the process of segmentation is carried on. Whether it is their nature first to go through a developmental stage outside of man, and to gain readmission in food or in drink, is not known.

Their great number, sometimes 300 or 400 together, leads to the belief that they may under favorable circumstances reproduce themselves in the original host. Any opening between the intestine and any cavity of the body may prove a loophole for its passage, and in this way its presence in strange places, as the bladder or abdominal cavity, may be accounted for. At all events, it is impossible for it to make an opening through the intestine or any tissue of the body, for it is without the means of doing so. The presence of ascarides has been attributed to illness and bad flour and bread. They are most abundant in moist localities, as seacoasts and river valleys, and they may gain admission to the intestines on raw fruit, or in mollusca and larvae of insects, which abound in such places. Bad food or the want of food will undoubtedly cause their discharge, as well as illness, but only because they are starved out, and because bad food and sickness generate an unhealthy action in the intestine, which thus becomes disagreeable to them.

So their discharge is more frequent in summer, but it is on account of the frequent diarrhoeas which follow the eating of green fruits and vegetables, by which they become sickly and are expelled, and not because they are generated by such food of itself; for it must take a long time for them to reach maturity, and they are seldom seen before this age. All attempts to produce these worms in the lower animals by administering eggs have thus far failed. The oxyuris or ascaris vermicularis, the thread or pin worm of the rectum, is the smallest of the human intestinal worms, the male being about two lines and the female five lines long.

Taenia echinococcus. a. Cyst, opened, b. Collection of Vesicles or Scolices. c. Single Scolex greatly magnified.

Fig. 5. - Taenia echinococcus. a. Cyst, opened, b. Collection of Vesicles or Scolices. c. Single Scolex greatly magnified.

Bothriocephalus latus, with View of Tail magnified.

Fig. 6. - Bothriocephalus latus, with View of Tail magnified.

Distoma he paticum.

Fig. 7. - Distoma he paticum.

Ciliated Embryo of Distoma.

Fig. 8. - Ciliated Embryo of Distoma.

Cercaria of Distoma hepaticum.

Fig. 9. - Cercaria of Distoma hepaticum.

Ascaris lumbricoides.

Fig. 10. - Ascaris lumbricoides.

1. Female. 2. Head. 3. Front view of head, showing the trilobulate form. 4. Tail. 5. Male.

Oxyuris ver micularis (female).

Fig. 11. - Oxyuris ver-micularis (female).

1. Natural size.

2. Magnified.

Trichina spiralis.

Fig. 12. - Trichina spiralis.

Its structure resembles that of its larger relative, and its head is also three-lobed, faintly marked. - The muscles of man are sometimes found after death to present a sanded appearance, which is caused by the presence of innumerable little cysts scattered throughout their substance; these are generally isolated, but in immediate contiguity. These minute bodies when examined microscopically are found to contain immature worms coiled up in the narrowest compass. They are cylindrical and tapering, 1/28 of an inch long by 1/600 of an inch thick, and their name is trichina spiralis. Both in the hog and in the human subject they are sometimes found in great abundance in the muscular tissue, sometimes as many as 70,000 or 80,000 to the cubic inch. When first discovered in 1832, and for many years afterward, they were supposed to be harmless, no symptoms connected with their presence having been detected. It is now known that in the cases first observed the parasites had long lain quiescent in the muscular tissue, and that their recent introduction into the system forms one of the most dangerous affections to which the human race is liable.

The true physiological history of trichina spiralis is as follows: When the muscular flesh of pork containing the encysted parasite is eaten in an uncooked or imperfectly cooked condition, the cysts are digested and destroyed in the stomach, but the worms themselves, retaining their vitality, pass into the small intestine. In this situation they lose their spiral form, and begin to increase in size; and by the fourth or fifth day they arrive at maturity, attaining a length of from 1/9 to 1/7 of an inch. At the same time the sexual organs are fully developed, copulation takes place, and the females become filled with mature eggs and embryos, which last are produced alive and in great abundance. These embryos, which are of minute size but in form similar to their parents, then begin to penetrate the walls of the intestine and to dispose themselves over the body. This causes at first an irritation of the intestine, which is usually the earliest symptom of the attack. Within a fortnight after the commencement of the symptoms the embryos are usually to be found scattered throughout the body and limbs, in the tissue of the voluntary muscles. They are still not more than 1/140 or 1/120 of an inch long.

They soon become enclosed in distinct cysts, where they grow to the size of 1/28 of an inch, and at the same time become coiled up in the spiral form. This period of the invasion of the muscular tissue by the parasite is one of great danger to the patient, being characterized by swelling and tenderness of the limbs, pain on motion, and general fever of a typhoid character. The attack is often fatal about the fourth week. If the patient survive that period, the trichina) become quiescent, cease their growth, and may remain without further development or alteration for an indefinite period. The only protection from danger of being infected with trichina from eating pork is to be sure that the meat is always thoroughly cooked throughout. - Tricocephalus dispar (fig. 13) is a nematoid worm which is found, rather rarely and in small numbers, in the cavity of the human caecum, and exceptionally in the colon or in the small intestine. Its anterior or cephalic extremity is slender and filamentous, while its posterior portion is thicker and more robust. The male, when extended, is about 1 1/2 in. long; the female 1 1/2 to 2 in. The eggs are ovoid in form, 1/500 of an inch in length, and marked at each extremity by a minute nipple-like projection.

They are discharged into the cavity of the intestine, and the embryo is developed only after a considerable time. This worm is not known to give rise to any disagreeable symptoms. - One more of the human entozoa is sufficiently interesting to be mentioned here at length, viz.: the filaria medinensis, or Guinea thread worm. This is confined to certain localities in the tropical regions. It is seldom over 9 ft. long, and is found of all lesser sizes according to its age. The male has not yet been described, for either its small size prevents detection, or else it never occurs in man. In shape the female resembles a flattened cord, one line in diameter. Its color is pale yellow, and it is viviparous. Its head is circular and armed with four straight pointed spines, by which it probably penetrates the tissues. It inhabits the subcutaneous areolar tissue, and chiefly that of the ankles, feet, and legs; but it has also been found in the abdominal parietes and arms. It often proves an endemic, attacking certain regiments in armies and sparing others. It appears to follow the rainy seasons, and to occur mostly in low and marshy districts.

There can be hardly any doubt that this animal is an inhabitant of wet places, and that man infects himself only by allowing it to come in contact with his skin. Those who take great precaution against wetting their feet, sleeping on the ground, and bathing in marshy pools, generally escape it. The worm may lie coiled up or extended at full length beneath the skin. As many as 50 individuals have been observed in one person, but usually one alone occurs. If superficial, its growth may be watched from day to day, and it has been seen to increase more than an inch in 24 hours. It often lies concealed for a long time without causing any symptoms of its presence, and may thus be borne from one country to another. When about to open externally, a little boil is found on the skin, which either bursts or is opened, and the anterior end of the worm protrudes. It is removed by seizing this and making gentle traction. All that readily yields is wound about a compress, and bound down over the wound till the following day, when the process is repeated till it is wholly extracted. Great care is taken not to break the worm, for serious results often follow such accidents.

It is probable that the young or germs inhabit wet soils, and enter the tissues of other animals to attain their full development after being impregnated outside. The attempt of the mature female finally to escape seems to imply that, its end being accomplished, it would return to its former home, and deposit its young, where new hosts may offer themselves for their reception. - Many other less important varieties of these three classes of entozoa have been described. - Medical Treatment. The administration of drugs in the encysted stages of tapeworm would of course be useless, and their diagnosis is often a most difficult problem. The following remarks apply then only to the intestinal forms. Nothing should be done until the passage of joints gives the infallible sign of the presence of the worm. All statements of patients regarding their own symptoms must be received with much doubt. A long catalogue of fearful and frightful ills is ascribed to their presence, but probably in the majority of cases without any cause whatever. It is true that the worm feeds upon the nutriment of the patient, but this has not yet formed a part of his organization, and is not assimilated.

Whether epilepsy is ever caused by tapeworm is a matter of great doubt, and more valid proof is needed to show more than a coincidence between the presence of the two. Some species cling more firmly than others, and are more difficult to dislodge. Of course, unless we obtain the head we fail, for the scolex may go on producing new colonies indefinitely. The only way to effect their removal is to render their habitation disagreeable to them. Various drugs (called anthelmintics) are employed to drive out these intruders. A brisk cathartic may dislodge one or two ascari-des if present, or bring away a piece of tapeworm. Cowhage (mucuna pruriens) and tin filings are now seldom used. Santonine, the active principle of santonica or semen contra, is used in doses of 3 to 6 grains three times a day. The oil of wormseed (chenopodium) is used in doses of 5 to 10 drops. Spigelia or pinkroot, alone or with senna, is a favorite anthelmintic in the United States, and the bark of the pride of China (melia azedarach) in the south. Tansy and wormwood, though not frequently used, may be added to the list. The small worms in the rectum are best treated with injections, either of ice water, salt water, infusion of quassia, lime water, or decoction of aloes.

The tapeworm is advantageously attacked with oil of turpentine, petroleum, the oleo-resin of male fern (aspidium filix-mas), pomegranate bark, kameela (from Rottlera, tinctoria), or by kousso, the flower of Brayera anthelmintic a. An emulsion prepared from the seeds of the common pumpkin has been used with very good effect, and has the merit of causing no disagreeable symptoms. Some of these drugs, as male fern, santonine, pome-grante, and kousso, produce more or less intestinal disturbance; and some, as santonine, pomegranate, spigelia, and azedarach, produce nervous symptoms. Benzine and picric acid have been suggested for destroying the trichina spiralis; but unfortunately the presence of this dangerous parasite is not likely to be recognized while accessible in the intestine, except during an epidemic, and it is not probable that any drug has power to dislodge or affect him after he has made his way into the tissues. It is said that the disease of sheep called rot, which is accompanied by the presence of these parasites in the biliary passages, does not occur where the bog bean (menyanthes trifoliata) or tornen-til grows, no matter how damp the pastures may be; nor are the sheep which feed in salt marshes or have salt mixed with their food subject to rot.

No remedies as yet discovered are of any avail in the treatment of the tre-matoda, and their presence can only be correctly diagnosticated when their passage into the outer world is observed. Among the nematoidea, the oxyurides, or pin worms, are the most troublesome, on account of the intolerable itching caused by their nightly wanderings outside the intestine. No treatment can wholly remove them, but cathartics and cold enemata are the best remedies. - The bibliography of helminthology has received many valuable additions within a few years, since it has become a distinct science. For a more complete account of its progress the following books may be referred to: Rudolphi, Entozoo-rum sive Vermium Intestinalium Historia Na-turalis (3 vols. 8vo, Amsterdam, 1808); Steen-strup, publications of Ray society, " Alternation of Generation" (London, 1845); Bremser, Ueber lebende Warmer im leoenden Menschen (4to, Vienna, 1819); Diesing, Systema Hel-minthum (2 vols. 8vo, Vienna, 1850); Dujar-din, Histoire naturelle des helminthes ou vers intestinaux (Paris, 1844); Van Beneden, Vers cestoldes ou acotyles (4to, Brussels, 1850); Leuckart, Blasenbandwurmer und ihre En-twickelung (4to, Giessen, 1856); Owen, "Lectures on Invertebrata" (8vo, London, 1843); Kuchenmeister and Von Siebold, translated in Sydenham society publications (2 vols. 8vo, London, 1857); Leidy, "A Flora and Fauna within Living Animals" (Smithsonian publications, vol. v., 4to, Washington, 1853); Wein-land "Human Cestoides" (8vo, Cambridge, 1858); Davaine, Traite des entozoaires (Paris, 1860); Leuckart, Untersuchungen uber Trichina spiralis (Leipsic, 1860); Cobbold, "Entozoa" (London, 1864); and Pagenstecher, Die Tri-chinen (Leipsic, 1865).

Tricocephalus dispar.

FIG. 13. - Tricocephalus dispar.

1. Male, natural size.

2. Male, magnified.

8. Female, natural size.