CHEMOTROPISM 151 



phenomenon which has no relation to chemotropism or 

 any other tropism. 



Buller had already observed that the supernatant sea 

 water of sea urchins contains a substance which causes 

 the agglutination of spermatozoa. 00 



A drop of sea water in which egg's had been deposited was placed 

 upon a slide and a drop containing spermatozoa near it. On joining 

 the drops a large number of small balls were formed in a very few 

 seconds. When very numerous spermatozoa were present the balls 

 became 0.1 mm. in diameter, containing many thousands of spermatozoa 

 packed together in a dense mass. 



Buller explains the phenomenon as being due to small 

 bits of egg jelly floating in the sea water 



so small that they will (like spermatozoa) pass through ordinary filter 

 paper and, so transparent that one cannot directly see them. A few 

 spermatozoa become attached to each piece of jelly, the presence of which 

 may be inferred from the manner in which the small groups of sperma- 

 tozoa move about. Owing to the length of the spermatozoon, although its 

 head may be imbedded in a jelly particle, the tail may remain partly free. 

 The little collections of spermatozoa thus move about hither and thither 

 in no particular direction. When two such groups come by accident 

 into contact they fuse. Certain of the spermatozoa adhere to both little 

 masses of jelly and lock them together. The fused mass combines with 

 other simple and fused masses, and so on. c 



The writer was able to show that when the jelly of the 

 egg of Strongylocentrotus purpuratus is dissolved by an 

 acid treatment the eggs when washed and transferred 

 to sea water no longer give off agglutinating substances, 

 while the acid sea water containing the dissolved jelly, 

 when rendered neutral through the addition of alkali, will 

 cause the agglutination of sperm. 302 While all the jelly 

 can be washed off with an acid treatment in the egg of 

 purpuratus, the same is not true for the egg of Arbacia 



cThis explanation of the fusion of two clusters to a larger one is per- 

 haps not correct. The writer is inclined to ascrihe it to the adhesion or 

 agglutination of the spermatozoa of two neighboring clusters with each 

 other, clue to a sticky surface on the sperm head. 



