270 



ANIMAL AGGREGATIONS 



concentrations, associated with increased density of the sperm sus- 

 pension used, as shown in Table XXX. 



The smallest quantity of sperm was so thin that it was unable to 

 fertilize all eggs even in sea-water, and the largest was so thick that 

 it was opalescent ; but the block to development did not shift beyond 

 6.9 to 7.1. Increasing the quantity of sperm increases the number 

 of eggs fertilized in acid solution, but the shift is not so great as 

 expected if the failure to fertilize were attributable to impairment 

 of sperm. The slight shift favors the belief that the block is due to 

 an alteration of the properties of the egg. Unless the sperm are in- 

 jured by toxic action of egg secretions, all eggs which are fertilized 



TABLE XXX 



Showing the Effect of Different H-ion Concentrations in COz-Free 



Sea- Water upon Fertilizing Power at Different Sperm Dilutions 



(Data from Smith and Clowes) 



in these solutions develop normally, indicating that the fertilization 

 reaction, when once initiated in the neighborhood of the block, is 

 completed without impairment. 



Before continuing with this search for further suggested explana- 

 tions of this phenomenon, it is of interest to stop for a moment over 

 the controversy concerning the mechanism of aggregation of sper- 

 matozoa in sperm suspensions. Lillie (19 19) points out that with 

 active spermatozoa in a suspension we should expect to find the 

 individual spermatozoa colliding with each other and with the walls 

 of their container, but that on the whole their distribution is ap- 

 proximately uniform throughout, much as is supposed to be the 

 case with gas molecules. This arrangement is found in perfectly 

 fresh suspensions, but usually lasts only a short time before various 

 kinds of aggregations occur. 



