Self -Fertilization Induced by Artificial Means. 169 



THEORETICAL. 



It has been often assumed by embryologists that there exists 

 some sort of attraction between the eggs and the spermatozoa of 

 the same species. This idea would readily suggest itself to anyone 

 who saw spermatozoa collecting in crowds around the eggs, but 

 it by no means follows that this phenomenon is really due to an 

 attracting substance emanating from the egg. The result may 

 be due to the membrane of the egg, to which those sperma- 

 tozoa stick that come accidentally into contact with it. In 

 fact I have observed similar collections of spermatozoa in the 

 ascidian around pieces of the body tissue, where the result had 

 every appearance of being due to some sticky substance, exuding 

 from the piece, rather than to an attraction exerted by the piece 

 on the spermatozoa. 



Pfeffer's oft-qiioted experiment M'ith tlie antherozooids of ferns, 

 liverworts, etc., appears to support the idea that the antherozo- 

 oids are attracted to the malic acid that is present in the neck of 

 the archegonia, but in the light of the recent experiments of Jen- 

 nings and others, as to the way in which unicellular forms accu- 

 mulate in a drop of acid, we can readily see that the results may 

 have a very different interpretation from that usually given to 

 them. Confining our discussion to the results obtained with the 

 ascidians, I offer the following tentative analysis of the problem : 



The failure of the spermatozoon of Ciona to enter the egg of 

 the same individual may be conceived as due to some physical ob- 

 stacle. It Is conceivable that pores may exist In the egg-membrane, 

 or even In the surface of the egg itself. This is the argument 

 that Ptliiger^ used in the case of cross-fertilization of the frog's 

 egg. If in the ascidian there existed a correlation of such a sort, 

 that the size of a spermatozoon of a given individual Is always 

 greater than the pores of the eggs of the same individual, then 

 self-fertilization could not take place. That this Is not the real 

 explanation Is shown by the fact that good spermatozoa are ap- 

 parently capable of fertilizing the eggs of all other individuals. 

 This would certainly not be the case if the exclusion of the sperma- 



1 Archiv. f. die gesammte Physiologic, XXIX., 1882. 



