668 ENTOZOA duce 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- mintlia, hooked worms. This group of en- tozoa, which resembles the nematoidea in form and distinction of sex, approaches more nearly the trematoda in its digestive system. It in- cludes some of the most noxious of the para- sitic helminths, but none infest man. They are included under one genus, echinorhynchus, which is characterized by its retractile probos- cis, armed with recurved spines. It is found in the intestines of the hog and other animals. Nematoidea, ccelelmintha (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 sys- tem or beneath the epidermis. They too un- dertake migrations and undergo transforma- tions, 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 dis- cover their mode of growth, has hitherto been possible only in a few species. They are dis- tinguished from the cestoidea and trematoda by a more elaborate digestive apparatus, by a ner- vous system, and by individuality of sex. Most of the species are oviparous, and the develop- ment of their eggs has been lately made the study of helminthologists. The ova are enclosed in hard shells, within which under suitable con- ditions the embryo is further developed by seg- mentation, till it breaks from its habitation, and comes forth either a perfect worm, or in an in- termediate form, in which it wanders into the tissues of man and other animals, where it may undergo the encysted stage, and finally on esca- ping become the mature individual, when it has found again a suit-able habitation. The largest of this class is the strongylm gigas, which be- longs to the dog and other animals, but which has been found at rare intervals in the human Iddney. 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, 8. equinus, is very common in the intestine of the horse, and S. 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- tricoides 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 mea- sures from 4 to 6, the female from 8 to 18 in. in length. The head is trilobulate with a con- striction below the papillae, which serve as suck- ing 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 segmen- tation is carried on. Whether it is their I nature first to go i through a develop- j mental stage outside ! of man, and to gain j 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 circum- stances reproduce themselves in the original host. Any opening between the intestine and any cavity of the body may prove a loop- hole for its passage, and in this way its I presence in strange places, as the blad- I der or abdominal cavity, may be ac- counted for. At all events, it is impos- sible 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 as- carides 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 in- sects, which abound in such places. Bad food or the Avant of food will undoubtedly cause their discharge, as well as illness, but only be- cause they are starved out, and because bad food and sickness generate an unhealthy action in the intestine, which thus becomes disagree- able to them. So their discharge is more fre- quent in summer, but it is on account of the frequent diarrhoeas which follow the eating of green fruits and vegetables, by which they be- FiG. 10. Ascaris lumbricoides. 1. Female. 2. Head. 8. Front view of head, showing the trilobulate form. 4. Tail. 5. Mate.
