152 E VOL UTION 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- 



