STUDIES OF FERTILIZATION 541 



3. Reaction to other acids 



The sperm of Nereis exhibits the same positive chemotaxis 

 to other acids as to CO 2. It is hardly necessary therefore to 

 enter into details. Sulphuric, hydrochloric, nitric, and acetic 

 acids were tested. They agree very closely with respect to the 

 effective dilutions; N/1000 dilution of any of these acids is an 

 effective chemotacticum agreeing quite closely in the degree of 

 the effect produced with 1 per cent CO 2; N/2000 may cause slight 

 ring formation in a drop introduced into a fresh sperm suspension, 

 but, if the suspension has reached the non-aggregative stage, no 

 reaction ensues, owing to the fact that the acid concentration in 

 question furnishes no gradient. 



Drops of stronger concentration cause a ring-shaped aggrega- 

 tion which continues to grow until diffusion eliminates the acid 

 gradient. None of these acids cause the least sign of agglutina- 

 tion of the spermatozoa whatever their strength. 



A drop of N/10 acid introduced within a sperm suspension 

 beneath a raised cover kills all the spermatozoa in its immediate 

 neighborhood, as the acid diffuses the zone of dead sperm increases 

 but as the margin of the diffusing acid reaches a dilution that is no 

 longer fatal it becomes marked by a clear border which is due to 

 the migration of sperm to it, even though they are carried into a 

 fatal concentration; and so the drop continues to grow so long as 

 an acid gradient remains. 



There is never the least sign of negative chemotaxis with respect 

 to any concentration of any acid, nor indeed of any other agent 

 tested. This being the case it is obvious that the aggregation of 

 the spermatozoa can not be by any trial and error method of 

 behavior, but must take place through orientation. 



4. Behavior with reference to alkalis 



The spermatozoa of Nereis do not exhibit any chemotactic 

 reaction, positive or negative, to drops of KOH or NaOH injected 

 into a suspension beneath a raised cover-slip. The drop remains 

 empty at first, and spermatozoa that enter it by chance are 

 agglutinated, so that in a short time the drop becomes filled 



