TABOO AND GENETICS 29 



show that some accident while this horse was 

 still a fertilized egg or a very small embryo 

 might have upset this male type of body 

 chemistry — perhaps even caused him to develop 

 into a female instead, if it took place early 

 enough. This is well illustrated by the so-called 

 " Free-Martin " cattle, to be described later. 



For a long time a controversy raged as to 

 whether sex is determined at the time of fer- 

 tilization, before or after. Biologists now 

 generally prefer to say that a fertilized egg is 

 " predisposed " to maleness or femaleness, 

 instead of " determined." The word " deter- 

 mined " suggests finality, whereas the embryo 

 appears to have in the beginning only a strong 

 tendency or predisposition toward one sex type 

 or the other. It is now quite commonly believed 

 that this predisposition arises from the quantity 

 rather than the quality or kind of factors in the 

 chemical impetus in the nuclei of the conjugat- 

 ing gametes. A later chapter will be devoted 

 to explaining the quantitative theory of sex. 



Hence the modern theory of " sex determina- 

 tion " has become : 



1, That the chemical factors which give rise 



to one sex or the other are present in 

 the sperm and ovum before fertiliza- 

 tion ; 



2. That a tendency or predisposition toward 



maleness or femaleness arises at 



