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. [Illustration: Fig. 66.--Strongylus gigas.--1, female, showing _a_, the mouth; _b_. the intestine; _c_, genital pore; _d_, anus. 2, cephalic extremity of the male; _a_, mouth; _b_, oesophagus. 3, caudal extremity of the male; _a_, cup; _b_, penis. 4, egg.] 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. [Illustration: Fig. 67.--Ascaris lumbricoides.--1, complete worm, 2, head, 3, tail of the male, 4, middle of the body of female.] 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.