226 W. V. LAMBERT AND C. \V. KNOX. 



hatching. Jull (1924) found a sex ratio of 47.18 in embryos 

 dying after the eleventh day of incubation taken as an average 

 of the results of continuous hatches throughout a three-year 

 period. Thomsen (1911) in a total of 805 embryos examined 

 before hatching found a ratio of 47.82, while Crew and Huxley 

 (1923) observed a prenatal sex ratio of 45.24 out of a total of 420 

 embryos examined. In the latter case, some of the parents of 

 the embryos were subjected to treatment with a thyroid extract. 



MATERIAL AND METHODS. 



The material for the present study was obtained primarily 

 from the FI and Fo generations and backcross chicks of crosses 

 made between the Rhode Island Red and White Leghorn breeds, 

 and also of FI data from crosses made reciprocally between the 

 Black Langshan and White Plymouth Rock, the Black Langshan 

 and Buff Orpington, and the White Plymouth Rock and Buff 

 Orpington. In addition a number of observations were made on 

 data from the White Leghorn breed. 



All eggs were candled on the sixth, twelfth, and eighteenth 

 days of incubation, and embryos found dead on these respective 

 days were classified as Di, D 2 and D 3 . All embryos found dead 

 between the eighteenth day of incubation and the day of hatching 

 were listed as dead in the shell (DS). All chicks of the D z 

 and DS classes, and chicks dying before it was possible to deter- 

 mine their sex from the external appearance, were dissected and 

 the sex determined in that manner. The sex ratio on all living 

 chicks was determined as soon as that was possible from their 

 external appearance. 



In 1925 the total sex ratio from 121 hens between the hatching 

 dates of March 4 and May 6 was obtained with the exception of 

 losses due to straying, loss of bands, predatory enemies, and 

 losses due to fire which destroyed a portion of the hatch of one 

 week. Data are given showing the number of individuals upon 

 which the sex was not determined, but there is no reason to believe 

 that the sex ratio of these chicks would have deviated greatly 

 from the ratios observed. 



In addition to the above, observations were made upon the 

 live chicks and dead embryos of a number of hens during the years 



