324 



MYRA MELISSA SAMPSON. 



sea-water for twenty to thirty-five minutes, a larger percentage 

 developed than in other experiments. In this series no ova 

 developed after exposure to hypertonic sea-water alone. In 

 Table VI. the results of these experiments are summarized. 

 The figures indicate approximate percentages. 



TABLE V. 



A COMPARISON OF THE NUMBER OF OVA OF Arbacia WHICH DEVELOP 



AFTER TREATMENT WITH FILTRATE FOLLOWED BY EXPOSURE 



TO HYPERTONIC SEA-WATER. 



Time of observation and total count = 70 hrs. 



The letters B, G, and P indicate blastulee, gastrulse, and plutei respectively. 

 The figures given here indicate the number, not the percentage, of developing ova. 



A comparison of the effects of the preliminary treatment with 

 sea-water and with sperm filtrates reveals, in the latter experi- 

 ments, a slight increase in the percentage of ova which develop 

 into plutei perfect in macroscopic appearance and in reactions; 

 and a decided increase in the percentage which cytolyze after 

 exposure to hypertonic sea-water. The preliminary treatment 

 with the sperm filtrate apparently sensitizes the ova to the action 

 of the hypertonic sea-water. 



Tests were also made to determine whether the sperm filtrates 

 increase the susceptibility of the ova of Strongylocentrotus 

 purpuralus to the action of hypertonic sea-water. Certain 

 preliminary experiments were performed to familiarize the writer 

 with the effect of hypertonic sea-water alone on the ova of this 

 species. Ova were exposed to it for periods of thirty minutes to 

 four hours. The effect was tested by transferring them to sea- 



