ch. xiv.J 18611871. 285 



kingdom generally. In studying this latter part of the sub- 

 ject he had to take into consideration the whole subject of 

 colour. I give the two following characteristic letters, in 

 which the reader is as it were present at the birth of a 

 theory. 



C. 1). to A. R. Wallace. Down, February 23 [1867]. 



Deak Wallace, I much regretted that I was unable 

 to call on you, but after Monday I was unable even to leave 

 the house. On Monday evening I called on Bates, and put 

 a difficulty before him, which he could not answer, and, as 

 on some former similar occasion, his first suggestion was, 

 " You had better ask Wallace." My difficulty is, why are 

 caterpillars sometimes so beautifully and artistically col- 

 oured ? Seeing that many are coloured to escape danger, I 

 can hardly attribute their bright colour in other cases to 

 mere physical conditions. Bates says the most gaudy cater- 

 pillar he ever saw in Amazonia (of a sphinx) was conspicu- 

 ous at the distance of yards, from its black and red colours, 

 whilst feeding on large green leaves. If any one objected to 

 male butterflies having been made beautiful by sexual selec- 

 tion, and asked why should they not have been made beau- 

 tiful as well as their caterpillars ; what would you answer ? 

 I could not answer, but should maintain my ground. Will 

 you think over this, and some time, either by letter or when 

 we meet, tell me what you think ? . . . 



He seems to have received an explanation by return of 

 post, for a day or two afterwards he could write to Wal- 

 lace : 



" Bates was quite right; you are the man to apply to in 

 a difficulty. I never heard anything more ingenious than 

 your suggestion, and I hope you may be able to prove it 

 true. That is a splendid fact about the white moths ; it 

 warms one's very blood to see a theory thus almost proved 

 to be true." 



Mr. Wallace's suggestion was that conspicuous caterpil- 

 lars or perfect insects (e. g. white butterflies), which are 

 distasteful to birds, benefit by being promptly recognised 

 and therefore easily avoided.* 



* Mr. Jenner Weir's observations published in the Transactions of the 

 Entomological Society (1869 and 1870) give strong support to the theory in 

 question. 



