Vol. VIII. May, 1^05. No. 6 



BIOLOGICAL BULLETIN 



SOME FURTHER EXPERIMENTS ON SELF- 

 FERTILIZATION IN CIONA. 



T. H. MORGAN. 



My previous experiments with Ciona intcslinalis had shown 

 that, by adding chloroform, or alcohol, or ammonia to the sea 

 water, self-fertilization could sometimes be effected, although in 

 this species self-fertilization does not usually take place in sea 

 water. The experiments did not show why under normal con- 

 ditions self-fertilization does not occur. Other results appeared 

 to indicate that the eggs offer a resistance of some kind to the 

 entrance of the spermatozoa of the same individual and that the 

 lack of fertilization is due to the failure of the spermatozoa to 

 enter, and not due to their failing to stimulate the eggs after enter- 

 ing. An analysis of the conditions led me to the conclusion that 

 the inability of the spermatozoa to penetrate eggs of the same 

 individual could not depend on differences in size of the mi- 

 cropyle of the egg that might be correllated, supposedly, with the 

 size of the spermatozoa of the same individual ; also that the fail- 

 ure was not due to the lack of some exciting substance present in 

 eggs of other individuals. I hazarded the guess that the resist- 

 ance offered by the egg to the entrance of its "own" sperm 

 might be due to some substance contained in the egg, or in its 

 membranes, that brings the spermatozoa of the same individual 

 to rest, and I pointed out that this view could be tested by the 

 following experiment. If the eggs of an individual (A) were 

 removed and allowed to stand in sea water, and if then this water 

 were poured off and the spermatozoa of the same individual (A) 

 were added to the water, they should be so affected that they 

 would fail to fertilize the eggs of another individual (B). I should 

 have made the proviso, as subsequent events have shown, that 



