ORGANIC RESPONSE 271 



weed butterfly, Anosia, by the viceroy butterfly, 

 Liminitis (see plate). The larva of the former 

 feeds upon the milkweeds, and it is supposed that 

 its body-fluids partake of the disagreeable taste of 

 the food-plant, and that on this account, being 

 conspicuously colored, it is avoided by butterfly- 

 hunting birds. Another group of butterflies not at 

 all closely related to Anosia is the genus Liminitis, 

 of which some seven or eight species are found in 

 North America. All of these but two are marked 

 with a white stripe across each wing and are very 

 different in appearance from Anosia. The impor- 

 tant exception is Liminitis archippus, which resembles 

 Anosia so closely in general appearance that unless 

 one were an entomologist he would hardly think 

 of discriminating the two when on the wing. The 

 advantage to Liminitis archippus of its masquerade 

 may be inferred from the fact that whereas Anosia 

 ranges over nearly the whole of North America and 

 the viceroy also, the other species of Liminitis have 

 very restricted and comparatively narrow ranges. 



For such mimicry to be successful it is necessary 

 that the mimic should vary widely from the type 

 of its congeners and that it should be much less 

 abundant than the " model." Natural Selection l 

 has usually been called upon to explain such a phe- 

 nomenon, but the theory offers many difficulties in 

 such a case, and scientists are far from agreed upon 

 an explanation. The fact of mimicry is, however, 

 indisputable. 



1 See next chapter. 



