23, i Schwartz: Life History of the Horse Oxyurid 47 



2. Oviposition is preceded by marked peristaltic movements of 

 the uterus, and following the expulsion of the eggs the females 

 become quiescent and exhibit no further signs of vitality. 



3. The eggs of Oxyuris equi develop rapidly and are embryo- 

 nated in about four days. 



4. Exposure of eggs to air appears to be requisite to develop- 

 ment. The moisture content of the eggs is protected by a gluey 

 water-insoluble substance, which accounts for the readiness with 

 which the parasites develop in a dry place. 



5. Continued exposure of embryonated eggs to environmental 

 conditions (dry and moist) results in a gradual lowering of 

 their vitality, and after a few weeks of such exposure they 

 lose their vitality entirely. 



6. Embryonated eggs of Oxyuris equi hatch in vitro, but the 

 larva- die in water as a result of plasmoptysis. The larva- 

 retain their vitality for a short time in physiological salt solu- 

 tion, and although they show sluggish movements they do not 

 molt in vitro. 



7. In guinea pigs hatching larvae were not observed in the 

 stomach. Emergence of larvae from the eggshell through the 

 birth pore in the shell that is guarded by the operculum occurred 

 in the small intestine. 



8. Oxyuris equi larva- were rapidly eliminated from the diges- 

 tive tract of guinea pigs, and no evidence of an invasion of the 

 liver, lungs, and other organs could be found in these animals. 



9. The life history of Oxyuris equi appears to be simple and 

 direct. Following oral infection, the larva- hatch in the intestine, 

 settle down in the caecum and colon, and by successive molts 

 attain sexual differentiation. 



10. On the basis of the foregoing observations it can be safely 

 concluded that the eggs of Oxyuris equi must be eliminated from 

 the host before development can take place, and that horses 

 become infected as a result of swallowing water or food that 

 has become contaminated with the eggs. 



REFERENCES TO LITERATURE CITED 



1. Cobb, N. A. Oxyuris larvae hatched in the human stomach under normal 



conditions. Proc. Linn. Soc. New South Wales II 6 (1890) 168-185. 



2. Fullerborn, F. Uber die Anpassung der Nematoden an den Para- 



sitismus und den Infektionsweg bei Ascaris und anderen Fadenwiir- 

 mern des Menschen. Archiv fur Schiffs- und Trop.-Hyg., Pathologie 

 und Therapie exotischer Krankheiten 24 (1920) 340-347J 



3. Graybill, H. W. Data on the development of Heterakis papillosa in 



the fowl. Journ. Exp. Med. 34 (1921) 259-270. 



