FERTILITY AND STERILITY IN DROSOPHILA 169 



These facts make it evident that incompatibility of some kind 

 had arisen between the egg and sperm of the inbred stock. It is 

 not evident that this is in any way related to the appearance of 

 the affected females in this strain. 



In regard to the method of transmission of the sterility as it 

 affects the female, Mast, one of Castle's students, came to the 

 conclusion that ''An entirely fertile male may transmit partial or 

 complete sterility of the female sex as a racial character to his 

 granddaughters though not apparently to his daughters. " Since 

 Castle and Mast's paper deals primarily with the effects of in- 

 breeding, the data upon which these conclusions are founded are 

 very small. As will be seen from my tables, this method of trans- 

 mission has been verified many times, the exception to be taken 

 here is that in all likelihood the partial fertility bears no relation 

 to the complete sterility. The reciprocal cross that led Mast 

 to the above conclusion 



. . . resulted in one case in the production of females half 

 of which were sterile and the other half were of low productiveness. 

 This case shows that a female of a race inclined to sterility may trans- 

 mit that character directly to her cross-bred offspring This 



difference in heredity through the two sexes would seem to indicate 

 that sterility of the female is dependent upon egg structure, the eggs 

 produced by mothers of a fertile race always yielding fertile daughters. 

 But the eggs of cross-bred females, whose father was of an infertile 

 race, produce some of them fertile, some infertile females. 



Such a method of transmission is not borne out in my cases. 

 The females transmit sterility to the granddaughters in the same 

 way as the males and it is certain that the defect skips a genera- 

 tion. Castle and Mast 's paper gives us no certain proof as to the 

 defect in the female. It seems to be assumed that she is laying 

 eggs but that these eggs are incapable of fertilization. If this is 

 true her sterility cannot be compared at all to that of the females 

 in my case. In all my experiments, however, I have never found 

 but one or two questionable cases in which the female having laid 

 her eggs proved sterile. In fact, toward the end of the experi- 

 ments it was easy to tell which sex was at fault by observing 

 whether or not the female was laying her eggs. While this was 

 never made the final test it always held good that when the female 



