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 
