io8 PROBLEMS OF FERTILIZATION 



H ion is the effective factor. The spermatozoa of 

 Arbacia exhibit a similar but much less pronounced 

 behavior and only to considerably higher concentration 

 of CO2, which agrees with their greater tolerance to 

 H ions. 



Alcohol is a substance which paralyzes the sper- 

 matozoa of Nereis at 5 per cent, and greatly decreases 

 activity at 2 per cent. However, it does not cause 

 aggregations similar to acids when tested under the 

 same conditions. But on the assumption that acid 

 aggregations are due to progressive paralysis, i.e., that 

 the acid acts as a trap, it is difficult to explain why 

 alcohol does not act similarly, though the difference is 

 readily understood if acids cause a specific form of be- 

 havior and alcohol does not. Nor do the spermatozoa 

 of Nereis exhibit any aggregation effect with reference 

 to drops of heated or cooled sea-water, which have 

 respectively activating and inhibiting effects. 



If the principle of chemotaxis may be regarded as 

 applying to spermatozoa in the foregoing sense, as 

 I believe to be the case, it is obvious that this form of 

 reaction may be of some significance in bringing the 

 egg and spermatozoon together in the process of ferti- 

 lization; we shall consider this subject later, but the 

 fact of capacity for chemotactic aggregation is of itself 

 by no means a proof that such aggregation is a factor 

 in fertilization. 



4. Reactions to Egg Secretions 



The reactions of spermatozoa to egg secretions of 

 their own and other species may obviously be of great 

 significance for the study of normal and hybrid ferti- 

 lization. In the study of this subject it is important 



