ON THE ORIGIN OF SEXUAL DIMORPHISM. 421 



Now, if we remove the generative organs — the origin of sexual 

 activity — we leave an animal purely vegetative, and one in which 

 none, or hardly any, of the secondar}'^ sexual characters will 

 make their appearance. They are not then part of the essential 

 vegetative basis of the animal, but a mere expression of its sex. 

 Remove the sex, and we remove them also. Can it then be said 

 that they are hereditary, even although the sexual activity from 

 which they arise be so ? I suggest that they are not, although 

 their partial appearance in some cases, even after the destruction 

 of the generative organs (if not due to an imperfect destruction), 

 would seem to show that perhaps they may eventually, after 

 many generations, become so. 



What I conceive to happen is somewhat as follows : — In 

 animals which exhibit neither sexual dimorphism nor seasonal 

 armature or ornamentation, the influence of the generative organs 

 is exerted equally upon the sexes, as well as, probably, through- 

 out life. In animals exhibiting the phenomenon either of 

 sexual dimorphism or seasonal armature or ornamentation, 

 the generative organs, when the individual is young, have 

 usually little or no influence on the body, which follows in its 

 growth the simplest possible laws. As soon, however, as the 

 generative organs commence to grow, their influence is usually 

 very marked. Their increase — often sudden, and, one might 

 almost say, violent — is effected at the expense of the other 

 organs, which, as in the case of the muscles of the Salmon, are 

 actually robbed of their material. The whole metabolism of the 

 body is disturbed, and the nervous system is particularly affected. 

 The pigment and material thus set loose is not necessarily 

 transferred in its entirety to the genitalia, but may, as in the 

 case of Oncorhynchus, find its way to the skin or elsewhere. I 

 have suggested that in some such cases the condition of the 

 animal is purely pathological. The heightened coloration is, as 

 in the human jaundice, the mere outward manifestation of disease 

 — a disease to which, in this case, the animal eventually succumbs. 

 There must, however, be numerous cases where the animal, al- 

 though sickening, survives. It is here that the power of Natural 

 or Sexual Selection supervenes as a guiding influence on the 

 manner and direction of the transference of pigment and matter. 

 This matter, at first transferred haphazard, is guided into 



