SOMATIC AND GENETIC STERILITY 



55 



and oviduct. It is, however, improbable that the physiological 

 tone of the bird had ever been sufficiently good to allow the 

 formation of yolk. Genetically the bird might have been 

 either a good or a poor layer. 



GENETIC STERILITY 



Bird No. 349 belongs to a family in which are individuals 

 with, and individuals lacking, both factors for high fecundity. 

 At autopsy this bird was in laying condition, with an egg in the 

 oviduct and a series of five growing yolks and four discharged 

 follicles in the ovary. Two of the three eggs recorded were 

 laid respectively on the day of death and the second preceding 

 day. These two eggs and the one in the duct account for three 

 of the four follicles. The other may have furnished the yolk 

 for a floor egg, explained as in the case of No. 383. There was 

 no yolk in the body cavity; the peritoneum was normal. This 

 bird had made no nesting records. Whether this bird was the 

 extreme of genetically poor layers or whether her sterility was 

 due to somatic causes too subtle for detection by rough autopsy 

 examination is impossible to state absolutely. The probability, 

 however, is extremely great that this bird genetically carries 

 .only Li or Lo — that is, has only one dose of any of the factors 

 on which production depends. This is evident from the follow- 

 ing considerations: 



X 9 different 9 9 



Sire d" No. 627 



Winter production Over 30 

 Observed 10 



9.6 



Under 30 

 13 1 



12.8 S. 



Zero " 

 (+No. 349, the 

 discussion 



bird under 



Ex-pected 



Now the dam of No. 349 was No. 303 J, whose genetic constitu- 

 tion wsiS fLiLo. fhk, with a winter record of 23 eggs, and a record 

 for the year of 79 eggs. Absolutely the most likely result of 

 mating such a bird with a Type 4 male, where, as in the present 

 case, there is only one in the family, is a bird which will make a 

 winter record under 30 — that is, one which carries but one dose 



