CLUSTER FORMATION OF SPERMATOZOA 125 



METHOD OF OBSERVATION AND THE SPECIFIC CHARACTER 

 OF CLUSTER FORMATION 



If we put one or more drops of a very thick sperm suspension 

 of the CaUfornian sea urchin, S. purpuratus, carefully into the 

 center of a dish containing 3 cc. of ordinary sea water, and let 

 the drops stand for one-half to one minute, and then by gentle 

 agitation mix the sperm with the sea water, the at first rather 

 viscous mass of thick sperm is in a few seconds distributed equally 

 in sea water and the result is a homogeneous sperm suspension. 



When the same experiment is made with the sea water which 

 has been standing for a short time in a dish over a large mass of 

 eggs of the same species, the result is entirely different. The 

 thick drop of sperm seems to be less miscible and instead of a 

 homogeneous suspension of sperm we get as a result the formation 

 of a large number of distinct clusters which are visible to the 

 naked eye and may possess a diameter of 1 or even 2 mm. The 

 rest of the sea water is almost free from sperm. These clusters 

 of spermatozoa last for from two to ten minutes and then dissolve 

 by^ the gradual detachment of the spermatozoa from the periphery 

 of the clusters. This phenomenon is to some extent specific. 

 The sperm of the sea urchin Strongylocentrotus purpuratus, will 

 give the cluster formation with the supernatant sea water of the 

 eggs of S. purpuratus; the sperm of the sea urchin S. franciscanus 

 will give the cluster formation \\^th the supernatant sea water 

 of eggs of its own kind as well as with the supernatant sea water 

 of the eggs of S. purpuratus. ' In the latter case the clusters dis^ 

 solve a little more quickly than if franciscanus sperm is added to 

 the supernatant sea water of franciscanus eggs. The sperm of 

 purpuratus will not form clusters with the supernatant sea water 

 of the eggs of franciscanus. It is of interest that the specificity 

 is not reciprocal in the case of these two sea urchins. 



The sperm of neither formed clusters with the supernatant 

 water of starfish eggs or of mollusc eggs. 



The sperm of starfish (Asterias ochracea and Asterina) gave no 

 cluster formation with the supernatant sea water of their own eggs 

 or of the eggs of the two sea urchins. 



