CHAPTER VIII 



Special Cases of Sex-Inheritance 



The mechanism of sex-determination that we have 

 examined gives equal numbers of males and females. 

 But there are known certain special cases where equality 

 does not hold. I have selected six such cases for 

 discussion. Each of these illustrates how the mechan- 

 ism of sex-determination has changed to give a different 

 result ; or how, the mechanism remaining the same, some 

 outside condition has come in that affects the sex ratio. 



It is so important at the outset to clearly recognize 

 the distinction between sex-determination and sex 

 ratio, that I shall take this opportunity to try to make 

 clear the meaning of this distinction. The failure to 

 recognize the distinction has been an unfailing source 

 of misunderstanding in the literature of sex. 



(1) A hive of bees consists of a queen, thousands of 

 workers, and at certain seasons a few hundred drones 

 or males. The workers are potentially females, and 

 these with the queen give an enormous preponderance 

 of females. In this case the explanation of the sex 

 ratio is clear. Most of the eggs laid by the queen are 

 fertilized, and in the bee all fertilized eggs become fe- 

 males, because as we have seen there is only one class of 

 spermatozoa produced, and not two as in other insects. 



There is a parallel and interesting case in one of the 

 wasps described by Fabre. The female lays her eggs 



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