276 THE AMEBIC AN NATURALIST [Vol. XLIX 



writer is, however, under the impression that no proof 

 for the existence of a positive chemotropism of the sea 

 urchin sperm for the eggs of the same species has thus 

 far been given. 



The writer observed that this phenomenon of sperm 

 agglutination depends on the motility of the sperm: 19 

 It only appears when the sperm is extremely motile and 

 it lasts only a number of minutes, often only a fraction 

 of a minute as Lillie had found. The writer observed 

 that the duration of the clusters depended to some extent 

 on the alkalinity of the solution. The more alkaline the 

 latter the more rapidly the cluster scatters. The pres- 

 ence of a salt with a bivalent metal, especially Ca, seems 

 necessary for the cluster formation. Sr and Ba act like 

 Ca and so does Mg but in the latter case a slightly higher 

 concentration is needed. The more Ca is added the more 

 powerful the agglutination becomes. These facts sug- 

 gest the following origin of the agglutination. From the 

 jelly surrounding the eggs a certain substance is dissolved 

 in the sea water which reacts chemically with a certain 

 substance at the surface of the spermatozoon. If this 

 reaction takes place in the presence of one of the salts 

 of a bivalent metal, especially Ca, a sticky precipitate is 

 formed on the surface of the spermatozoa, which is slowly 

 soluble in the solution ; and the more rapidly the more al- 

 kaline the solution. If the spermatozoa are very active 

 the impact with which they strike each other may lead to 

 their sticking together and this agglutination will last 

 until the precipitate is dissolved again. 20 



The writer mentions this fact here because it might give 

 us a clue to the role of the motility of the spermatozoon 

 for its entrance into the egg. One can imagine that the 

 spermatozoon must stick to the surface of the egg in or- 

 der to be taken into it and this sticking may not come 

 about unless the spermatozoon strikes the surface of the 



10 Loeb, Jour. Exper. Zool., XVII, 123, 1914. 



Lillie measures the degree of agglutination by its duration; if our as- 

 sumption is correct he really measures the time required for the solution of 



