Ch. XIV.] 1861—1871. 269 



I can, enough to work a little, I hope my life may be very short, 

 for to lie on a sofa all day and do nothing but give trouble 

 to the best and kindest of wives and good dear children is 

 dreadful." 



The " Chapter on Man," which afterwards grew into the 

 Descent of Man, was interrupted by the necessity of correcting 

 the proofs of Animals and Plants, and by some botanical 

 work, but was resumed with unremitting industry on the 

 first available day in the following year. He could not rest, 

 and he recognised with regret the gradual change in his mind 

 that rendered continuous work more and more necessary to 

 him ae he grew older. This is expressed in a letter to Sir 

 J. D. Hooker, June 17, 1868, which repeats to some extent 

 what is given in the Autobiography : — 



" I am glad you were at the Messiah, it is the one thing that 

 I should like to hear again, but I dare say I should find my 

 soul too dried up to appreciate it as in old days; and then 

 I should feel very flat, for it is a horrid bore to feel as I 

 constantly do, that I am a withered leaf for every subject 

 except Science. It sometimes makes me hate Science, though 

 God knows I ought to be thankful for such a perennial interest, 

 which makes me forget for some hours every day my accursed 

 stomach.' 



The Descent of Man (and this is indicated on its title-page) 

 consists of two separate books, namely on the pedigree of 

 mankind, and on sexual selection in the animal kingdom 

 generally. In studying this latter part of the subject 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. 



0. D. to A. B. Wallace. Down, February 23 [1867]. 



Dbab 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 coloured ? 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 caterpillar he ever saw in Amazonia (of a 

 sphinx) was conspicuous at the distance of yard s> from its 



