152 EVOLUTION AND DISEASE. 
of new characters by the male, or at any rate increased 
functional importance of certain organs possessed, when 
in the state of hermaphroditism, by all the forms. By 
natural selection the male would acquire (or, if already 
in his possession in a functional condition, would 
gradually develop) means for seizing and retaining 
the female, such as the claspers of sharks, the callous 
pads of frogs, &c. Paternal duty requires the male to 
protect the young and defend the females from harm ; 
hence horns, teeth (as in the musk-ox), spurs, tusks, &c., 
become more developed in him. 
The duties of the female require her not only to furnish 
the material out of which the young are to be formed, 
but in many cases she is required to provide them with 
nutrition long after they enter the world. The material 
which the female thus provides is of the very kind neces- 
sary, in many instances, to build up such structures as 
horns, tusks, teeth, and the like. Further, this material 
is required by the female at the corresponding period of 
life in which these structures become developed in the 
male, viz.,on the advent of puberty. We may state with 
certainty, that a distinct correlation exists between the 
generative organs of the female and the development of 
the secondary sexual male characters. The more de- 
veloped and functional the female reproductive organs 
become, the less likely is she to manifest the secondary 
characters of the male. It may be argued, that in some 
cases the female simulates the male, as in the few 
examples of female deer possessing horns. Quite true ; 
but so long as the female is engaged in the duties of 
reproduction, these secondary characters are never de- 
