SPERM FILTRATES AND DIALYZATES. 323 



that used by Loeb, has succeeded in producing healthy viable 

 plutei of Arbacia punctulata by exposing ova of this species to 

 hypertonic sea-water alone. In view of these results it may be 

 that the butyric acid sensitizes the eggs to the action of the 

 hypertonic sea-water. Experiments were undertaken to de- 

 termine whether or not sperm filtrates may also act as sensitizers. 



The procedure employed in this phase of the investigation was 

 as follows: unfertilized eggs of Arbacia were exposed for periods 

 of one minute to two hours to a sperm filtrate and subsequently 

 for twenty to thirty-five minutes to Loeb's hypertonic sea-water. 

 A control series consisted of ova exposed first to sea-water and 

 then to Loeb's hypertonic sea-water. One set of unfertilized 

 and one set of fertilized eggs served as controls for each experi- 

 ment. 



In the majority of experiments no development took place in 

 the ova exposed to hypertonic sea-water only. When such an 

 exception occurred, the percentage of ova which developed was 

 small and the plutei did not swim at the surface of the water. 

 In every experiment many of the ova subjected to the double 

 treatment, i.e., to the filtrate followed by the hypertonic sea- 

 water, developed as far as the blastula and gastrula stages. A 

 small percentage developed into perfect plutei which swam at 

 the surface. The majority cytolyzed. Because of the high 

 percentage which cytolyze at the time when the blastulae and 

 gastrulae form, it is impossible to determine the exact percentage 

 which develop to. these stages. The sea-water containing them 

 was centrifuged and the residue examined. An effort was made 

 to ensure the transfer of equal quantities of eggs and of sea- 

 water in each experiment, and equal periods of centrifuging 

 were employed to ensure equal possibilities of precipitation of 

 ova or of developing individuals. The results of these experi- 

 ments are given in Table V. 



As already indicated the sperm filtrates rarely cause membrane 

 formation. In the few instances where these form, they are 

 thin and but slightly elevated. In one filtrate such membranes 

 developed on ova after an exposure to the filtrate for thirty to 

 thirty-five minutes. Of the ova remaining in the filtrate for 

 one to fifteen minutes and subsequently transferred to hypertonic 



