THE SEGREGATION OF FECUNDITY FACTORS 

 IN DROSOPHILA. 



By EDWARD N. WENTWORTH. 



The inheritance of qualitative characters according to the Mendelian 

 scheme is so well established that even the practical breeder questions 

 no longer, but quantitative differences are still somewhat slow in 

 yielding evidence of their accord to this system. Nilsson-Ehle, Shull, 

 East and other plant breeders have indicated the means by which such 

 inheritance may take jilace, while Phillips has shown an interesting 

 example in size in duck crosses. The heredity of fertility is a subject 

 of practical importance in manj' species, and the problem resembles 

 those which the investigator has to attack in the genetics of size, vigor, 

 etc. Pearl has made an excellent contribution to the knowledge of 

 the subject in his recognition of a sex-linked fecundity factor in the 

 domestic fowl but beyond this paj)er little work has been done. 



The inception of the present experiment was rather accidental. 

 Early in September 1912 mice gained access to the writer's cultures 

 of Drosophila and either devoured or liberated nearly everything. 

 From the wreckage three pupae of orange-eyed flies were rescued 

 which hatched one male and two females. As one female died before 

 mating the idea of making an experimental study to see what would 

 come from inbreeding was conceived. The foundation pair were then 

 average flies in appearance and possessed of the orange-eyed character. 



The -F] generation, if it may be so termed, was composed of 

 126 flies. Fi'om these four lines were started. The largest and most 

 vigorous males were mated with the largest and most vigorous females, 

 the rather weak and small flies were mated together and two lines of 

 medium type, one based on size and the other on apparent vigor 

 were also established. These divisions were not based on any actual 

 measurements, but rather on general appearance and impression. 

 Fortunately the divisions were justified although later generations 



