152 TROPISMS 



of Woods Hole. Here the acid treatment does not as a rule 

 dissolve all the jelly, or possibly some new jelly may be 

 given off by the egg. 



While Buller may be correct in assuming that micro- 

 scopic pieces of the egg jelly form the center of these 

 sperm clusters, the writer reached the conclusion that 

 the dissolved mass of the jelly makes the surface of the 

 spermatozoa transitorily sticky, so that if they impinge 

 against each other they will stick together for some time, 

 until the sticky compound formed by the jelly on the sperm 

 head is dissolved by the sea water, which occurs after a 

 short time. 



This agglutinating effect of the egg- sea water upon 

 the sperm of Arbacia gives rise to that ring formation 

 which Lillie considers a proof of positive chemotropism. 

 When a drop of egg-sea water is put into a sufficiently 

 dense suspension of spermatozoa, the spermatozoa at the 

 surface of the drop will agglutinate into practically one 

 dense ring around it, and through the diffusion of some 

 of the dissolved jelly through this ring numerous little 

 clusters will form at the external periphery of the ring, 

 and these clusters will fuse with the ring. In this way 

 the clear region behind the ring originates. The process 

 of fusion continues inside the ring with the result that 

 the latter breaks up into numerous bead-like spherical 

 clusters as Lillie described. In a former paper the writer 

 has pointed out the analogy between the phenomena of 

 transitory sperm agglutination (under the influence of 

 egg-sea water) and surface tension phenomena, inasmuch 

 as two small clusters upon coming in contact fuse into one 

 larger one and inasmuch as elongated clusters break up 

 into two or more spherical clusters. 



The ring formation described by Lillie has, therefore, 



