SPERM FILTRATES AND DIALYZATES. 327 



or to filtrate and hypertonic sea-water, failed to develop. Occa- 

 sionally atypical membranes formed after the double treatment 

 and irregular division ensued. It is of interest that ova which 

 had been exposed to the filtrate for two hours did not shrink 

 when transferred to hypertonic sea-water, as did those transferred 

 directly from sea-water to the hypertonic sea-water. This would 

 seem to indicate that the permeability of the ova exposed to 

 the filtrate had increased. Another indication of the effect of 

 the filtrate in these experiments follows: Ova given the double 

 treatment of filtrate followed by hypertonic sea-water were less 

 capable of normal fertilization and development than those 

 exposed to hypertonic sea-water alone. 



Summary of the Function of Filtrates as Factors in Parthenogene- 

 sis. Exposure of ova oi Arbacia punctulata or of Strongylocentrotus 

 purpuratus to sperm filtrates of the same species produce changes 

 which render them more susceptible to the action of hypertonic 

 sea-water. This is indicated in Arbacia by a larger percentage of 

 development and of cytolysis; and in S. purpuratus by a greater 

 tendency of ova to cytolyze or to lose their power of normal 

 fertilization and development if exposed to both filtrate and 

 hypertonic sea-water. 



VI. FILTRATES AS FACTORS IN FERTILIZATION. 



The increase produced by sperm filtrates in the susceptibility 

 of Arbacia ova to parthenogenetic agents, and the apparent 

 increase in permeability of ova of 5. purpuratus suggest that 

 such preparations may also facilitate fertilization. 



An attempt was made to obtain "resistant" eggs early in the 

 breeding season in order to try the effect of fertilizing such ova 

 in sperm filtrates. During two seasons such "resistant" eggs 

 were not found. The ova obtained were either immature, as 

 indicated by their failure to develop if fertilized with a small or 

 large amount of sperm suspension, or else ripe. In the latter 

 case no increase over the usual percentage of development could 

 be expected. 



Conditions leading to increase in permeability of mature ova 

 tend to allow the entrance of more than a single spermatozoon 

 when such eggs are inseminated. This polyspermy usually 



