434 



PEARL— SEX RATIO IN DOMESTIC FOWL. 



The figures for the sex ratio of the dead embryos for the years 

 1916 and 1917, the only ones for which complete records are at 

 hand, are given in Table XI. 



TABLE XL 



Sex Ratio of Embryos Dying Between the Tenth Day of Incubation 

 AND Hatching. Various Breeds. 



These numbers are large enough so that the results are clearly 

 reliable. And it is equally clear that this portion of the prenatal 

 mortality is not differential in respect to sex. For the season of 

 1916 the sex ratio of the living chicks at hatching was 



ie^ = 48.3 ±0.89, 



a value not significantly different from that for the prenatal mor- 

 tality given in Table XL The sex-ratio figures for the living 

 hatched in 1917 are not available at the time of writing, but it is 

 evident enough, if we compare the figures of Table XI. with those 

 of Table VI. (p. 422), that there is no differentiation in respect of 

 sex of the mortality of the last eleven days of the prenatal life of 

 the zygote. 



Cole and Kirkpatrick's' data for pigeons appear to indicate that 

 probably the prenatal mortality in that form is not differential. It 

 must be said, however, that they take account of only a small amount 

 of the total prenatal mortality, those dying at the very end of incu- 

 bation, then group this with the post-natal mortality of the first five 

 days after hatching. The general impression given by this data, 

 however, is that the prenatal mortality is probably not differential 

 in the pigeon. 



It is evident from the data of Table XL, that the explanation 

 for the preponderance of females in poultry is not to be found in 

 the greater frequency of deaths of males during the last eleven 



