ILLUSTRATIVE OF NATURAL SELECTION. 157 



in similar localities, while the males, which frequent 

 the sunny open river-banks, have a totally different 

 colouration. In these cases, therefore, natural selec- 

 tion seems to have acted independently of sexual 

 selection ; and all such cases may be considered as 

 examples of the simplest dimorphism, since the off- 

 spring never offer intermediate varieties between the 

 parent forms. 



The phenomena of dimorphism and polymorphism 

 may be well illustrated by supposing that a blue-eyed, 

 flaxen-haired Saxon man had two wives, one a black- 

 haired, red-skinned Indian squaw, the other a woolly- 

 headed, sooty-skinned negress and that instead of the 

 children being mulattoes of brown or dusky tints, 

 mingling the separate characteristics of their parents 

 in varying degrees, all the boys should be pure Saxon 

 boys like their father, while the girls should altogether 

 resemble their mothers. This would be thought a 

 sufficiently wonderful fact ; yet the phenomena here 

 brought forward as existing in the insect-world are 

 still more extraordinary ; for each mother is capable 

 not only of producing male offspring like the father, 

 and female like herself, but also of producing other 

 females exactly like her fellow-wife, and altogether 

 differing from herself. If an island could be stocked 

 with a colony of human beings having similar phy- 

 siological idiosyncrasies with Papilio Pammon or 

 Papilio Ormenus, we should see white men living 

 with yellow, red, and black women, and their off- 

 spring always reproducing the same types ; so that 



