CLUSTER FORMATION OF SPERMATOZOA 135 



ing cluster formation of sperm. It is interesting that Lillie states 

 that such eggs lost also their power of causing agglutination, which 

 seems to suggest that Lillie 's 'agglutination' and the writer's 

 'cluster formation' may be the same thing. Lillie states that such 

 eggs which have formed a fertilization membrane have lost their 

 power of being fertilized and he sees in this a support of his theory 

 that without 'fertilizin' the egg can no longer be fertilized. 



Eggs which have formed a fertilization membrane under the 

 influence of butyric acid can easily be fertilized with sperm if the 

 membrane is torn by shaking. The writer has repeated this 

 experiment this winter and confirmed the earlier observations 

 by Kupelwieser and himself to the same effect. He also made sure 

 that the eggs which after the artificial membrane formation can 

 be fertilized with sperm have completely lost the power of causing 

 cluster formation. 



We thus see that complete loss of the. power of inducing cluster 

 formation can be combined with maximal power of the eggs of 

 being fertilized. 



HYBRIDIZATION AND CLUSTER FORMATION 



The best test for a possible connection between fertilization and 

 cluster formation is afforded in the phenomena of hybridization. 

 If the phenomenon of cluster formation were inseparably associ- 

 ated with the power of the eggs of being fertilized, we should 

 expect that sperm should only be able to fertilize the eggs of a spe- 

 cies if the egg-sea water of the same species caused the cluster 

 formation of the sperm. 



It Is easy to show that no connection of this type exists. It is 

 impossible to call forth cluster formation of the spermatozoa of 

 the starfish Asterias ochracea with the egg-sea water of purpuratus 

 and yet 100 per cent of the eggs of purpuratus can be fertilized 

 with the sperm of ochracea and as many as 80 per cent of these eggs 

 may develop. The writer showed that this hybridization takes 

 place only in hyper-alkaline sea water and it was therefore nec- 

 essary to test the possibility of cluster formation in both neutral 

 and alkaline sea water; these tests gave always absolutely negative 

 •results. 



