536 



FRANK K. LILLIE 



tozoa. At the same time there is of course diffusion of substances 

 pecuhar to the general suspension towards the introduced drop; 

 but that conditions thus arising are ineffective is shown by the 

 fact that no reaction is given to the introduced drop of pure sea- 

 water. We may, therefore, leave this centripetal diffusion out of 

 account. It should be remembered that 1 per cent CO 2 sea-water 

 is the minimum paralyzing strength for Nereis sperm. 



Fig. 5 Diagram of the reaction of a sperm-suspension of Nereis to an introduced 

 drop of 1 per cent CO2 sea-water; explanation in the text. 



The diagram therefore shows, that migration of the spermato- 

 zoa proceeds up the gradient to, or near to, the point of paralysis 

 of the spermatozoa; for in the case of the drop of 1 per cent CO 2 

 sea-water the ring forms well within the original margin of the 

 drop. With higher and lower dilutions of CO2 the width of the 

 clear margin is practically the same. 



The effects of greater and less CO2 concentration than the 

 1 per cent used in the initial experiment are interesting. In general 

 the use of a gi*eater concentration involves a larger aggregation, 

 and of a less concentration a smaller aggregation. Thus if a 

 drop of sea-water saturated with CO2 be introduced into a sus- 

 pension of fresh sperm beneath a raised cover slip a border of 

 dead or paralyzed sperm forms at its margin, and shortly a clear 

 zone forms external to it; the spermatozoa migrate in large 



