60 S Indies in the Theory of Descent. 



warmth would always change a given colour * in the 

 same manner in all butterflies, and would there- 

 fore always give rise to the production of the same 

 colour. But this does not occur ; Polyommatus 

 Phl&as, for example, becoming black in the south, 

 whilst the red-brown Vanessa Urticce becomes black 

 in high northern latitudes, and many other cases 

 well known to entomologists might be adduced. 2 

 It indeed appears that species of similar physical 

 constitution, i.e., nearly allied species, under similar 

 climatic influences, change in an analogous man- 

 ner. A beautiful example of this is furnished 

 by our Pierince. Most of the species display 

 seasonal dimorphism ; as, for instance, Pieris 

 Brassica, Rap a, Napi, Krueperi, and Daplidice, 

 Eiichloe Belia and Belemia, and Leucophasia 

 Sinapis, in all of which the difference between the 

 winter and the summer forms is of a precisely 



1 [Assuming that in all butterflies similar colours are pro- 

 duced by the same chemical compounds. R.M.] 



a [Mr. H. W. Bates mentions instances of local variation in 

 colour affecting many distinct species in the same district in 

 his memoir " On the Lepidoptera of the Amazon Valley ;" 

 Trans. Linn. Soc., vol. xxiii. Mr. A. R. Wallace also has 

 brought together a large number of cases of variation in colour 

 according to distribution, in his address to the biological section 

 of the British Association at Glasgow in 1876. See "Brit. 

 Assoc. Report," 1876, pp. 100 no. For observations on the 

 change of colour in British Lepidoptera according to distri- 

 bution see papers by Mr. E. Birchall in " Ent. Mo. Mag ," 

 Nov., 1876, and by Dr. F. Buchanan White, " Ent. Mo. Mag./' 

 Dec., 1876. The colour variations in all these cases are ot 

 course not protective as in the well-known case of Gnophos 

 obscurata, &c. R.M.] 



