210 PROBLEMS OF FERTILIZATION 



rates of development are about the same for self- and 

 cross-fertilized eggs. 



In this table each letter stands for an individual, 

 the capital for the eggs and the small letter for the 

 sperm; thus Aa, Bb are self-fertilizations, Ab, Ba, and 

 Ca cross-fertilizations. An excess of sperm was used in 

 all the fertilizations; the difference in percentage of 

 eggs fertilized when selfed and crossed should be noted. 

 The eggs that are fertilized segment and hatch in the 

 same time, whether selfed or crossed; but the selfed 

 eggs do not survive, while the crossed eggs do. This 

 was the invariable result in a considerable number 

 of experiments, except that in one selfed lot some of 

 the larvae settled down, and four survived over a 

 month. 



It is clear from the discussion that the incompati- 

 bility of the self- sperm manifests itself in the cortical 

 reaction; for some reason the spermatozoon fails to 

 fuse with the egg, and as a consequence the activation 

 of the egg fails. This result is incidentally another 

 strong proof that the process of union of the gametes is 

 not a mechanical boring-in action of the spermatozoon. 

 The experiments may also be regarded as demonstrat- 

 ing that if the cortical barrier is once passed the other 

 processes of fertilization proceed normally. 



Morgan (1910) in his analysis of the subject con- 

 cludes that the failure to self-fertilize is due to the 

 absence of a reaction between the egg and the sperm; 

 and elsewhere (1913) he attributes this to the similarity 

 of the hereditary factors carried by the egg and the 

 sperm. The context of his analysis implies that he 

 is thinking of a chemical reaction of the character 



