Sex Determination i8i 



Hertweg's experiments, using toads' eggs. Taking some 

 newly laid eggs she withdrew water from them, then 

 allowed them to be fertilized, and the resulting progeny 

 were 90 per cent females. The obvious conclusion is that 

 eggs with low water content produce females. 



Finally, there is the remarkable work of Riddle (ii) 

 with pigeons. Hertweg and Miss King had found 

 that sex is determined by the physiological factor of 

 water content. Riddle has investigated a little more 

 critically, analyzing the physiological conditions of both 

 male and female, and gives the following contrast: 



Male Female 



High percentage of water Low percentage of water 



Low percentage of fat High percentage of fat 



Low percentage of phosphorus High percentage of phosphorus 



High metabolism Low metabolism 



It appears from this that high water, low fat, and 

 low phosphorus are male attributes or conditions, 

 while the female attributes are the reverse. The main 

 feature of difference, however, to which the other con- 

 trasting conditions are subordinate is that the male 

 shows high metabohsm and the female low metaboUsm. 

 The idea is that any physiological conditions that 

 affect water content or fat content or phosphorous con- 

 tent in the egg will affect the sex in the resulting 

 progeny. 



Following these ideas. Riddle was able to control 

 sex by various means; furthermore, he makes the 

 somewhat startling statement that sex is a quantitative 

 phenomenon; that is, the difference between male and 

 female is a difference in degree only. A diagram 

 (fig. 40) will illustrate the situation. It represents a 



