42 The Philippine Journal of Science 1923 



fore, that oxygen is an essential factor in the development of the 

 egg of Oxyuris equi. 



Within from twenty-four to thirty-six hours after oviposition 

 individual blastomeres could be made out only with difficulty, 

 and in many instances could no longer be distinguished, because 

 the outline of the embryo became evident (Plate 1, fig. 4). 

 Within from forty-eight to sixty hours after oviposition devel- 

 opment had proceeded to the stages shown in Plate 1, figs. 5 

 and 6. The embryos showed a definite orientation in the shell, 

 the knoblike constricted portion being located at the opercular 

 end. Cultures of eggs seventy-two hours old showed a sausage- 

 shaped embryo (Plate 1, fig. 7) which exhibited sluggish move- 

 ments. Ninety-six-hour cultures showed embryonated eggs, 

 the embryos exhibiting lively and continuous movements within 

 the shells. 



LONGEVITY OF EMBRYONATED EGGS 



Although the eggs of Oxyuris equi offer considerable resist- 

 ance to lack of moisture and to absence of oxygen, and although 

 the embryonated eggs retain their vitality for some time even 

 though they are kept dry until the egg masses lose their glisten- 

 ing appearance, prolonged subjection of the eggs to unfavorable 

 conditions results in their gradual loss of vitality and, ulti- 

 mately, in death. Newly formed embryos were active within 

 the shell despite the fact that they were kept in a dry place. 

 After several days' drying the embryos were inactive in the 

 shell but resumed their activities rapidly when moistened. At 

 this stage hatching readily occurred in vitro. After two or 

 three weeks' drying the larvae appeared sluggish when mois- 

 tened, and many showed no movement within the shell. Such 

 eggs were still viable, because when they were fed to guinea 

 pigs they hatched in the small intestine. Embryonated eggs 

 that were kept dry on slides for about six weeks appeared 

 wrinkled within their shells and, although but few had under- 

 gone pronounced degeneration, the intact forms showed no 

 movement when moistened, were paler in appearance than 

 normal larvae, and failed to respond to heat stimulation. Larva- 

 kept in a moist beaker for a similar period showed more- 

 pronounced symptoms of degeneration. It is thus evident that 

 the embryonated eggs of Oxyuris equi, though resistant to un- 

 favorable conditions for a short time after the formation of 

 the embryo, succumb to environmental conditions after several 

 weeks. 



