TABOO AND GENETICS 6i 



the clutches also tend to produce males all 

 along. In both cases, the male-producing eggs 

 were found to be the ones with the smaller 

 yolks. Family crosses also produce small 3^olks, 

 which hatch out nearly all males. Some pairs 

 of birds, however, have nearly all female off- 

 spring. Riddle investigated a large number of 

 these cases and found the amount of yolk 

 material to be large. In other words, there 

 seems to be a definite relation between the 

 amount of yolk and sex. 



A great number of clever experiments were 

 carried out to find out if eggs originally pre- 

 disposed to one sex were actually used to pro- 

 duce the other. Selective fertilization with 

 different kinds of sperm was impossible, since 

 in these birds there is only one type of sperm — • 

 two of eggs — as to the sex chromosome. For 

 instance, by overworking females at egg-pro- 

 duction, the same birds which had been pro- 

 ducing more males than females were made to 

 reverse that relation. 



One of the interesting results of the experi- 

 ments was the production of a number of inter- 

 sexual types of various grades. This was easily 

 verifiable by colour and other characteristics. 

 To make sure that the instincts were corre- 

 spondingly modified, behaviour was registered 

 on moving-picture films. Where the first egg 

 of a clutch (the one with a small, normally 



