FERTILITY AND STERILITY IN DROSOPHILA 167 



It is to be recalled that Castle in his cultures found both males 

 and females sterile. Moenkhaus found in his strain, in 64 cases 

 tested, that the males alone were sterile.- Moenkhaus in attempt- 

 ing to harmonize Castle 's results with his own points out that the 

 two cases can not with certainty be compared since Castle took no 

 account of the emergence of larvae but merely the production of 

 pupae. In other words, Castle 's measure of productiveness was 

 eggs that gave rise to pupae; Moenkhaus 's measure, the emergence 

 of larvae. From my studies this difference seems rather apparent 

 than real since in only one or two very questionable cases have I 

 found that larvae aftei* emerging from the egg were unable to 

 develop to the adult stage. I do not wish to be misunderstood 

 on this point. Not every zygotic combination, as is evident from 

 my later studies, results in the production of a well formed fly. In 

 fact, the percentage, as I have been able to show, may be very low. 

 Whether the sperm enters the egg, or having entered the combi- 

 nation dies, is another question. The fact holds in my strains 

 that if the larvae emerge some of them develop to the hatching 

 stage. 



1 wish to point out that my results and those of Castle are more 

 likely to be harmonized on the asumption that a distinction exists 

 between fertility and sterility. Castle and Moenkhaus seemed 

 to consider that the defect related to sperm and egg structure. I 

 infer from Castle's paper that he supposed that sterile females 

 occurred more frequently in a strain inclined to low productivity; 

 that low fertility and complete sterility as it affects the female are 

 causally related. I interpret him to mean that there is a range in 

 the capacity of the eggs for" fertilization by good sperm, extend- 

 ing from zero (or complete sterility) to high fertility. In my 

 strain no such condition is involved; but it is conceivable that 

 the egg-laying power ranges in degree from zero to complete 

 productivity. If so some of the sisters of the sterile females 



2 He mentions one exception which from the present standpoint seems signifi- 

 cant. "In one instance I found among a brood, beside a sterile male, two females 

 that failed to deposit eggs although eggs were evidently present in the oviducts." 

 It seems likely that this is the same defect that I have found so prevalent in my 

 cultures. 



