62 TABOO AND GENETICS 



male-producing yolk) produces a female, she is 

 usually found to be more masculine than her 

 sister from the second egg with the larger yolk. 

 This is true both as to appearance and as to 

 behaviour. Some of these were quite nearly 

 males in appearance and behaviour, though 

 they laid eggs. 



Testicular and ovarian extracts were injected. 

 The more feminine birds were often killed by 

 the testicular extract, the more masculine by 

 the ovarian extract. Finally, to make assurance 

 doubly sure, some females which should theo- 

 retically^ have been the most feminine were dis- 

 sected and shown to be so. That is, out-crosses 

 which produced a predominance of females in 

 the fall were mated with females which had 

 been overworked at egg production until they 

 threw nearly all females. Dissecting the females 

 thus produced, they were shown to have right 

 ovaries, which means double femaleness, since 

 normally the pigeon is functional only in the 

 left ovary, like other birds. The right one 

 usually degenerates before or at hatching and 

 is wholly absent in the week-old squab. 



In pigeons, Riddle thinks the " developmental 

 energy " of the eggs is in an inverse ratio to 

 their size. The last and largest eggs of the 

 season develop least and produce most females. 

 The second egg of a clutch is larger than the 

 first, but develops less and the bird produced 



