50 Sterile and Hybrid Pheasants 



large number of cases, so that the irregularities of chance are ruled 

 out. 



The first numbers that will be given refer to the sterile hybrids 

 raised by crossing Reeve's % with males of P. torquatas, var. formo- 

 sanus, and P. versicolor. The numbers are as follows : — 



Infertile and Dead in 



Total eggs Addled shell Sex Totals 



99 68 1 6? 16<f 



The sex-ratio is here 6 ? to 16 (/ or 266 per cent, of males. The 

 especially interesting point brought out by these figures is the fact 

 that the number of birds which died in the shell is only one, so that 

 the disproportion in the sexes cannot be accounted for by supposing 

 that more female birds died in the shell than males. The cause of the 

 disproportion must be sought for at an earlier stage, cither at so early 

 a stage of developement that no trace of a developing chick could be 

 detected in the egg, or else at fertilisation itself. In other words the 

 disproportion of the sexes appears to be due not to a selective mortality 

 of the sexes, but to something tantamount to selective fertilisation. 



We may now give the total figures relating to all the cross-bred 

 pheasants raised by Mrs Haig Thomas. It must be noted that these 

 cross-bred pheasants were not sterile hybrids in the strict sense of the 

 term though they exhibit a considerable degree of sterility. The 

 crosses were mostly between Silver and Swinhoe Pheasants, and Golden 

 and Amherst, and Formosan and versicolor. 



Table of Sex-ratios in Hybrid Pheasants. 



Note. The death-rate of hatched birds from 1909—1912 was 143 males to 55 females 

 thus showing a preponderance of deaths among males. 96 out of the total 1522 eggs were 

 not incubated. 



The sex-ratio is here 135 $ to 228 </ or 168 per cent, of males. 

 This percentage represents a considerable drop from that obtained from 



