MELANIC VARIATION IN LEPIDOPTERA. II7 



The only other manner in which such protection might be 

 supposed to arise would be perhaps owing to the strong contrast 

 which would exist between the extreme whiteness of snow and 

 the darker appearance of large or small patches of herbage in its 

 immediate proximity, rendering the latter more nearly black to 

 the perception, at least of human sight, than they would actually 

 be if separated from the shining snow. 



It may be admitted that this contrast would render a dark 

 object under such circumstances less visible than a lighter one. 

 But the amount of protection afforded by reason of these special 

 conditions would appear inadequate to account for any strong 

 hereditary tendency to strive to obtain it. 



Coming to the question of archaic derivation the researches 

 and experiments of Weismann * and Edwards f may be admitted 

 to have established a well supported theory that in cases of 

 seasonal dimorphism and polymorphism, one or other of the 

 varieties produced is probably that which has descended through 

 the longest period from an ancestral form. Both these authors 

 have called attention to the fact that there is less disposition to 

 vary in the female sex, and if the females are truly more con- 

 servative than the males, we should be inclined to look to the 

 former sex as most likely to indicate the typical colouration of an 

 archaic race. 



Mr. MacLachlan | pictures the survivors of an arctic fauna 

 moving northward as increasing temperature succeeded the 

 glacial period, a portion of them settling on the tops of high 

 mountains, stragglers reaching the home of their ancestors, and 

 becoming the progenitors of our present arctic species ; but he 



* ' Studies in the Theory of Descent,' vol. i, and Appendix; English 

 edition. 



f ' Butterflies of North America,' and 'Canadian Entomologist,' vol. 

 vii, pp. 228 — 240 ; vol. ix, pp. I — lO, 51 — 55, 203—206. 



+ Journal of Linnean Society, (Zoology) 1878, xiv, p. 105. 



