40 



While I was studying these wonderful experiments the 

 following correspondence appeared in " Knowledge " : — 



" Knowledge " September, 1903. 

 Protective resemblance in Butterflies. 



Sir, 



Some years ago I made a collection of butterflies in the 

 district of Santos, Brazil, and amongst them are two specimens 

 obtained from the granite quarries, which in colour and mark- 

 ings exactly reproduce the texture of granite. I have no doubt 

 this is an instance of ordinary protective resemblance, for I 

 remember how difficult it was to see these butterflies when once 

 they had settled on the granite surface. The point, however, 

 which strikes me as of considerable interest is that the general 

 colouring of the butterflies is a cool blue grey exactly the shade 

 of the freshly quarried stone on which it invariably settled. 

 The weathered surfaces of the granite were greenish grey. The 

 fact seems to point to the very rapid evolution of the butterfly's 

 present colouring, since the quarries in question have probably 

 only existed for some two or three hundred years and before 

 that time the butterflies could not have found access to a freshly 

 cleft granite surface. I am not entomologist enough to name 

 the butterfly but would send a photograph to anyone interested. 

 I should be glad if any of your correspondents who have studied 

 the question of protective colouring could say whether there is 

 any warrant for concluding that a change in colour of the kind 

 indicated could be evolved within so limited a period. 



(Signed) W. S. Rogers. 



[This observation is of much interest, and there can be 

 little doubt that the colour of the species has changed during 

 the period mentioned under the influence of natural selection. 

 During the last half of the nineteenth century British entomo- 

 logists have noticed a distinct tendency on the part of certain 

 moths, normally of a pale grey colour, to be replaced by dark 

 varieties, in the manufacturing districts of the north of England, 

 where the habitual resting-places of the insects — palings, tree- 

 trunks, etc. — tend, through the deposition of soot, to be darker 

 than usual. It must be remembered that a century or two is a 

 comparatively long period in the life of a species of insect. 



(Signed) G. H. Carpenter.] 



