23,1 Schwartz: Life History of the Horse Oxyurid 45 



small intestine where it molts twice. Cobb,(D on the other 

 hand, found that Enterobius vermicularis hatched in the human 

 stomach when capsules containing these eggs were swallowed. 

 Cobb states that the capsules were not dissolved and that a 

 considerable amount of gastric fluid entered them. It is pos- 

 sible, of course, that the larva? in Cobb's experiments emerged 

 from the shells before the gastric fluid entered the capsules. 

 In view of the rapid disappearance of the larva? from guinea 

 pigs, no observations on molting were made. Repeated fa?cal 

 examinations of guinea pigs that were fed Oxyuris eggs failed 

 to reveal any larva?, and it may be taken for granted that these 

 were digested in the intestines of these animals. 



Whether the failure to find larvse in the lungs and liver of 

 guinea pigs that were fed eggs of Oxyuris equi may be accepted 

 as conclusive proof that migrations to these organs do not occur 

 in the course of the life cycle of these parasites is impossible 

 to determine definitely from the data at hand. It is probable, 

 however, that such migrations do not occur in the life history 

 of Oxyuris equi, development being simple and direct following 

 ingestion of embryonated eggs. 



Following the discovery of the migrations of the larva? of 

 various Ascaridse, attempts were made by various investigators 

 to discover migrating larvse in the life history of more or less 

 common nematodes, but these attempts have been in the main 

 unsuccessful. Thus Fullerborn(2) failed to observe migrations 

 of larva? of Trichuris trichiura, a nematode parasitic in the 

 lower portion of the digestive tract of man, whose morphological 

 affinities with Trichinella spiralis, a nematode whose larva? invade 

 the blood stream, warranted the expectation that a migration of 

 larva? would probably occur. Fullerborn observed, contrary to 

 his expectations, the beginning of development of these larva? in 

 the csecum of rabbits and guinea pigs. Graybill(3) and Riley (?) 

 likewise report negative results with Heterakis papillosa, a nema- 

 tode parasitic in the ca?cum of chickens and other birds, whose 

 development following ingestion of embryonated eggs took place 

 in the normal habitat of this parasite. I have repeatedly fed 

 the eggs of Ascaridia perspicillum, a nematode parasitic in the 

 intestines of chickens, to guinea pigs and chicks and I have 

 been unable to demonstrate migrations of the larva? despite 

 careful and tedious examinations of the liver, lungs, and other 

 organs. On the contrary, I found that the larva? develop in 

 the lower portion of the small intestine of guinea pigs and 

 chicks where they increase considerably in size. Ransom, (6) 



