254 EDITH PINNEY 



results reveals a number of facts that may be of value in an 

 attempt to explain the results of hybridization on the basis of 

 cytological processes. 



1. Concerning the factors conir oiling mitosis 



The egg of Ctenolabrus cooperates normally with the spermato- 

 zoon of three different species during the early cleavage divisions. 

 Newman recognized the superiority of the hybridizing powers 

 of the eggs of certain species over those of other species. From 

 his experiments he concludes that "The three species which 

 h^^bridize with the largest degree of success have small eggs, those 

 of Tautogolabrus [Ctenolabrus], Stenotomus and Menidia." 

 "Considering the rather large size of the eggs of Fundulus hete- 

 roclitus . . . these eggs hybridize with rather marked suc- 

 cess." The results which he gives ('16) p. 556, table 2, show 

 that he obtained hatching embryos from five crosses with 

 Tautogolabrus (Ctenolabrus) and from three crosses with each 

 of the species, Fundulus, Stenotomus, and Menidia. Of these 

 three species, Fundulus gives the smallest total number of 

 hatching larvae and Stenotomus ranks next to Ctenolabrus in 

 the matter of producing individuals capable of hatching. New- 

 man thinks that the eggs of these species contain yolk which is 

 more easily digested than that in eggs of lower hybridizing quality. 



Cytological observations have shown that the egg of Ctenola- 

 brus is better adapted to cooperate in mitosis with the sperm of 

 foreign species than are the eggs of either of the other three 

 species used, Fundulus, Stenotomus, and Menidia. 



I have already expressed the idea that the factors which 

 determine whether or not a foreign spermatozoon shall take part 

 normally in the mitotic processes are attributes of the egg. The 

 fact that eggs of one species show the same behavior when fertil- 

 ized by the spermatozoa of several different species; that the 

 cleavage rhythm in hybrids is a function of the egg; that normal 

 mitosis occurs in crosses in which development does not proceed 

 very far; and, further, that the development of reciprocal hybrids 

 is often very unlike, all offer strong support for this view. Fur- 

 ther, if one consider the early appearance of abnormalities in 



