320 



MYRA MELISSA SAMPSON. 



franciscanus at Pacific Grove, California, from January to June 

 1921, yielded similar results. Longer exposures were required 

 than with ova of Arbacia. The ova of S. franciscanus were the 

 more susceptible to the action of the sperm filtrates, but un- 

 fortunately ripe ova of this species were rare during these months 



--> '/ 



GRAPH X. The effect of limited exposure of ova to sperm filtrates Arbacia. 

 Experiment 156 Observation at the end of twenty-four hours. The percentage 

 of ova divided and cytolyzed is indicated. A = sea-water. B = exposure to 

 5 per cent.* nitrate for five minutes. C = exposure to 5 per cent, filtrate for ten 

 minutes. D = exposure to 5 per cent, filtrate for thirty minutes. E = exposure 

 to 5 per cent, filtrate for sixty minutes. F exposure to 5 per cent, filtrate for 

 twenty-four hours. 



of 1921 because of an extremely cold season. It is well known 

 that the ova of 5. purpuratus are resistant to parthenogenetic 

 agents, Loeb (1916, pp. 99-103). The hope that the conditions 

 of low temperature (i2-i5 C.) and high hydrogen-ion con- 

 centration (p H 7.6-7.8) prevailing at Pacific Grove might favor 

 normal segmentation and normal development of ova treated 

 with sperm filtrates was not realized. Yet, as will be demon- 

 strated in later experiments, a brief exposure to such filtrates 



* 5 per cent, filtrate = a filtrate from a 5 per cent, suspension. 



