326 



MYRA MELISSA SAMPSON. 



water and to inseminated sea-water. Ova treated for thirty 

 minutes to two hours were uninjured. Longer exposures caused 

 cytolysis of ova transferred to sea-water and prevented normal 

 fertilization and development of ova subsequently inseminated in 

 sea-water. The percentage of the ova affected bore a direct 

 relation to the duration of the exposure to the hypertonic sea- 

 water. 



A repetition of Loeb's method of producing parthenogenesis in 

 this species demonstrated that treatment with 1.5 per cent, 

 butyric acid for one minute followed by hypertonic sea-water 

 for one hour led to development of the majority of the ova. 

 Other experiments indicated that a slight decrease in hydrogen- 

 ion concentration (e.g., p H 8.3-8.7) facilitated the process. In place 

 of the butyric acid ova were given a preliminary treatment with 

 sperm filtrates in the hope of obtaining development, or of 

 intensifying the action of the hypertonic sea-water. The results 

 at the end of eighteen hours are indicated in Table VII. 



TABLE VII. 



EFFECT OF EXPOSURE TO FILTRATE FOLLOWED BY HYPERTONIC SEA-WATER ON 

 OVA OF Strongylocenlrotus purpuralus. 



It has already been mentioned that ova of Strongylocentrotus 

 purpuralus are more resistant to parthenogenetic agents than 

 are those of Arbacia punctulata. In these experiments ova of 

 the former species, exposed either to hypertonic sea-water alone 



