_A. lumbricoides_ Linn. is one of the largest known Nematodes ♂ = 4-6 in., ♀ = 10-14 in.; Figs. 66 and 67). It is a common parasite in man, and has been found in the ox. It is now generally recognised as the same parasite which inhabits the pig, and which Dujardin regarded as specifically distinct, and named _A. suillae_. In the latter host, however, it never attains the dimensions it does in man. It inhabits the upper and middle parts of the small intestine, and has been known to escape into the body-cavity and set up abscesses there, or to make its way into the stomach, and to be voided through the mouth. It is practically cosmopolitan in distribution, and is very common in Japan—Baely found it in twenty-one out of twenty-three _post-mortems_—and in Tonquin and tropical Africa. Heller[177] states that no one is free from these worms in Finland, and they are common wherever there is a plentiful water supply, as in the marshy districts of Holland and Sweden. In Iceland alone they seem absent. When examined alive they give off an irritating vapour which seriously affects some observers, causing catarrhal symptoms, which in Bastian's case lasted six weeks. The usual number found in one host is small, one to six or eight, but cases are on record where many hundreds occurred in one person. The details of the life-history of this form are not yet completely worked out. The eggs leave the body of the host with the excreta, and formerly it was thought they re-entered the alimentary canal in drinking-water, etc., and there developed into the adult without change of host. This view has been combated by Leuckart, who failed to rear the Nematodes by direct feeding, and it has been noticed that the youngest parasites found in the {140}intestine are already 2 to 3 mm. long. Von Linstow has recently suggested that the larval stages may be hatched out in the body of the millipede _Julus guttulatus_, whose habits might easily lead it to eat the eggs of the parasite in manured gardens, etc., and which is itself sometimes unconsciously eaten when hidden in fruit or vegetables. This would account for the frequent presence of the parasite in pigs, and also for the fact that in man it is commonest in children who are apt to eat windfalls, and in maniacs and people with perverted tastes.