No. 581] ENTRANCE OF THE SPERMATOZOON 211 



egg with a certain velocity. This is, however, merely a 

 suggestion. The really serious difficulty of such an as- 

 sumption lies in the fact that the specific and transitory 

 cluster formation or agglutination of the spermatozoa is 

 not a general phenomenon. It may even turn out to be 

 confined to sea urchins and certain annelids. It is prob- 

 ably lacking in all cases of hybridization. Yet this would 

 not necessarily speak against the possibility of an ag- 

 glutination of the spermatozoon to the egg as a prerequi- 

 site of fertilization. 



This latter idea receives some support in the writer's 

 experiments on heterogeneous hybridization. He was 

 able to show that both NaOH as well as CaCl 2 , which 

 render possible the fertilization of the eggs of certain sea 

 urchins through the sperm of starfish, also favor the ag- 

 glutination of that sperm to the chorion of the egg. This 

 leads to the peculiar phenomenon of mere membrane for- 

 mation in the egg by the living spermatozoon without the 

 entrance of the latter into the egg. 21 



VI 



Lillie seems to take it for granted that the substance of 

 the egg which causes sperm agglutination is identical 

 with the substance which stimulates the spermatozoa into 

 greater activity. If this were correct the conditions for 

 the two phenomena should be identical, which is however 

 far from being the case. 



The writer showed that if we deprive the eggs of pur- 

 puratus of the jelly which surrounds them and if we wash 

 them afterwards a few times in sea water to deprive them 

 of the last vestiges of jelly substance which may still ad- 

 here to them they have lost completely and permanently 

 the power of forming clusters with the sperm of their 

 own species. Such eggs were washed four times in m/2 

 NaCl and when a drop of the supernatant NaCl solution 

 was added to NaCl sperm of purpuratus which was not 

 motile it activated the sperm very powerfully. 



The writer had found that the egg sea water of S. fran- 



"Loeb, Arch. f. Entwckliu]«mcch., XL, 310, 1914. 



