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THE AMEBIC AX NATURALIST [Vol. XLIX 



the egg if the sperm of the same species is mixed with the 

 sperm or the blood of a species widely apart. If, for 

 instance, the sperm of a sea urchin is mixed with the 

 sperm of certain annelids (Chcetopterus) or molluscs and 

 if after some time the eggs of the same sea urchin are 

 added to the mixture of the two kinds of sperm no egg is 

 fertilized. If the solution is, however, subsequently 

 diluted with sea water or if the egg that was in this 

 mixture is washed in sea water, the same sperm mixture 

 in which the egg previously remained unfertilized will 

 now fertilize the egg. From these and similar observa- 

 tions He riant 1 2 draws the conclusion that the block 

 existed at the surface of the egg, inasmuch as a reaction 

 product of the two types of sperm is formed after some 

 time which alters the surface of the egg and thereby pre- 

 vents the sperm from entering. This view is not only 

 supported by all the experiments but also by the observa- 

 tion of the writer that foreign sperm or blood is able to 

 cause after some time a real agglutination if mixed with 

 the sperm of a sea urchin or a starfish. 13 We can imagine 

 that the precipitate forms a film around the egg and 

 acts as a block which can be removed mechanically by 



It is not impossible that the block which exists in the 

 fertilized egg is due also to an alteration of the physical 

 character of the surface of the egg which in this case is, 

 however, induced from within the egg by changes caused 

 by the entrance of the spermatozoon, which, however, are 

 not necessarily identical with those causing development 

 as was shown by the facts in the second chapter. 

 IV. 



We will now turn to the question whether the motility 

 of the spermatozoon plays no other role than to bring the 

 spermatozoon so close to the surface of the egg that sur- 



into the egg. It is easy to show that if the spermatozoa 



