Chapter I. 



Sexual Dimorphism and the Secondary 

 Sexual Characters. 



When we speak of sexual dimorphism we refer to the morpho- 

 logical and physiological differences between the two sexes, 

 differences which relate to other characters besides the 

 dimorphism of the generative cells. In so doing we recognise 

 two different groups of sexual characters : first, the generative 

 cells or the primary sexual characters, and, secondly, the so- 

 called secondary characters. But the term "secondary sexual 

 characters" is not always used in the same sense. By "secon- 

 dary sexual characters" one often means those morphological 

 and physiological characters which are directly connected with 

 the sexual functions (the actual generative cells being the 

 primary sexual characters), all the other differences between the 

 sexes being called "tertiary" characters. On the other hand 

 all the morphological and physiological differences between the 

 sexes, other than the generative cells, are sometimes designated 

 secondary sexual characters. Disputes about the boundary 

 lines between the characters designated primary or secondary 

 sexual characters have bulked largely in scientific literature. 

 These terminological polemics merely show an insufficiency of 

 knowledge of the facts. The standpoints taken up by those who 

 have been engaged in controversy as to the meaning of the 

 terms primary, secondary and tertiary sexual characters 

 reflect individual opinions on the value or importance of 

 the different characters in relation to the sexual and repro- 

 ductive functions. Some authors assess a higher value and 

 some a lower to a particular character according to their 

 opinions as to its precise functions. And as our knowledge is 

 still very incomplete, it is easy to understand that the opinions 

 of various authorities as to what are primary, secondary and 

 tertiary characters differ widely from one another. 



The distinction between primary and secondary sexual 

 characters might be based also on another wholly different 



