258 EDITH PINNEY 



the permeability of the egg, Gray puts forward the hypothesis 

 that the effects of hybridization in sea-urchins are due to changes 

 in the permeability of the egg, which differ according to the species 

 of sperm that is used. The crosses with fishes do not bear out 

 the idea that the effects of hybridization are a function of the 

 spermatozoa, for ill three crosses with the same egg and different 

 spermatozoa the same result was obtained, namely, normal 

 nuclear division ; while in three crosses in which the same species 

 of spermatozoa was used to fertilize three different species of eggs, 

 the outcome, though not the same in each of the three crosses, 

 was similar in that abnormal behavior of the chromatin was 

 noted in each. The greatest interest for us here lies in the 

 fact that artificial treatment of the eggs can modify the character 

 of mitosis, demonstrating that it is the condition of the cyto- 

 plasm that governs the nuclear behavior and not the interacting 

 germ plasms, for in this case the two parental germ plasms are 

 the same. 



4. The respective roles of the germ nceclei and the cytoplasm of the 



egg in fish hybrids 



In spite of the fact that a great deal of variation occurs in the 

 individuals obtained from one cross, rather broad differences in 

 the developmental success of the various crosses may be recog- 

 nized, and from table 1 a curious relation existing between the 

 crosses listed there may be noted. In the cross in which nuclear 

 behavior is abnormal the greatest success in development occurs 

 in the more distantly related species, while, in cases in which 

 mitotic behavior is normal, the converse is true, the highest 

 success in development is obtained in crosses between the more 

 closely related species. 



The cases in which the behavior of the chromatin has been 

 studied are as yet almost too few to warrant a general application 

 of this statement, but the idea is one that will bear testing. It 

 is reasonable to think that the results of a cross will be more 

 nearly an expression of the relationship between the two inter- 

 acting germ plasms if the cytoplasm of the egg furnishes no hin- 



