136 JACQUES LOEB 



The sperm of purpuratus shows no trace of cluster formation 

 with the egg-sea water of franciscanus and yet the eggs of fran- 

 ciscanus are readily fertilized with the sperm of purpuratus. 



If the cluster formation were caused by a substance which was 

 necessary for fertilization in the sense of Lillie's theory these and 

 probably many other hybridizations which occur should be 

 impossible. 



It often happens that in hybridization less than 100 per cent 

 of the eggs are fertilized. The writer tried whether the yield of 

 fertilized eggs could be increased if the egg-sea water from the 

 species which furnishes the sperm be added to the mixture. This 

 would furnish the sperm with the specific ' amboceptor. ' It was 

 found that hybridizations occur just as well if not better in normal 

 sea water than if the egg-sea water from the species from which 

 the sperm is taken be added. 



All these facts contradict the assumption that the substance 

 which induces the cluster formation of the spermatozoon is nec- 

 essary for fertilization. 



ARTIFICIAL PARTHENOGENESIS AND CLUSTER FORMATION 



The writer has expressed the idea that the causation of the de- 

 velopment of the egg either by a spermatozoon or by the agencies 

 of artificial parthenogenesis is due to an alteration of the cortical 

 layer of the egg which may or may not be accompanied by a 

 membrane formation; and he has shown that all hemolytic sub- 

 stances are able to bring about this alteration. Lillie agrees with 

 this idea but differs in regard to the origin of the agent which 

 causes this change in the cortical layer of the egg in the case of 

 fertilization by a spermatozoon. According to the writer, this 

 change is caused by a substance contained in the spermatozoon 

 while Lillie assumes that it is a substance contained in the egg 

 which must, however, be activated by the spermatozoon in order 

 to cause the alteration of the surface of the egg. It seems to the 

 writer that Lillie's asslnnption is unnecessarily complicated. 

 Moreover, if it should turn out that the substance which is re- 

 sponsible for the cluster formation is identical with the substance 

 which Lillie calls 'fertilizin' — which is very likely the case — 



