Specificity in Fertilization 83 



seconds and the result is a homogeneous sperm sus- 

 pension. When, however, the same experiment is 

 made with the sea water which has been standing for 

 a short time over a large mass of eggs of the same spe- 

 cies, the thick drop of sperm seems to be less miscible 

 and instead of a homogeneous suspension we get, as a 

 result, the formation of a large number of distinct 

 clusters which are visible to the naked eye and which 

 may possess a diameter of I or 2 mm. The rest of the 

 sea water is almost free from sperm. These clusters 

 of spermatozoa may last for from two to ten minutes 

 and then dissolve by the gradual detachment of the 

 spermatozoa from the periphery of the cluster. 



This phenomenon seems to occur in sea urchins and 

 annelids. The writer has vainly looked for it in differ- 

 ent forms of the Californian starfish or molluscs and 

 in fish at Woods Hole. Lillie failed to find it in the 

 starfish at Woods Hole. 



The writer found that the sperm of the Californian 

 sea urchin Strongylocentrotus purpuratus will form clus- 

 ters with the egg sea water of purpuratus but not with 

 that oifranciscanus; while the sperm of franciscanus will 

 agglutinate with the egg sea water of both species, 

 but the clusters last a little longer with the eggs of 

 its own species. 



He also found that the clusters are more durable in 

 a neutral than in a slightly alkaline solution and that 

 the agglutination disappears the more rapidly the 



