278 Colour and the Struggle for Infe 
Nearly a year later Darwin in his letter of May 5, 1868?, expressed 
his agreement with Wallace’s views: “ Except that I should put 
sexual selection as an equal, or perhaps as even a more important 
agent in giving colour than Natural Selection for protection*.” The 
conclusion expressed in the above quoted passage is opposed by 
the extraordinary development of Protective Resemblance in the 
immature stages of animals, especially insects. 
It must not be supposed, however, that Darwin ascribed an 
unimportant role to Cryptic Resemblances, and as observations 
accumulated he came to recognise their efficiency in fresh groups of 
the animal kingdom. Thus he wrote to Wallace, May 5, 1867: 
“ Hickel has recently well shown that the transparency and absence 
of colour in the lower oceanic animals, belonging to the most different 
classes, may be well accounted for on the principle of protection®.” 
Darwin also admitted the justice of Professor E. S. Morse’s con- 
tention that the shells of molluscs are often adaptively coloured’. 
But he looked upon cryptic colouring and also mimicry as more 
especially Wallace’s departments, and sent to him and to Professor 
Meldola observations and notes bearing upon these subjects. Thus 
the following letter given to me by Dr A. R. Wallace and now, by kind 
permission, published for the first time, accompanied a photograph 
of the chrysalis of Papilio sarpedon choredon, Feld., suspended from 
a leaf of its food-plant : 
July 9th, 
Down, 
Brecxennam, Kent. 
My Drear WALLACE, 
Dr G. Krefft has sent me the enclosed from Sydney. A 
nurseryman saw a caterpillar feeding on a plant and covered the 
whole up, but when he searched for the cocoon [pupa], was long 
before he could find it, so good was its imitation in colour and form 
to the leaf to which it was attached. I hope that the world goes well 
with you. Do not trouble yourself by acknowledging this. 
Ever yours, 
Cu. DARWIN. 
Another deeply interesting letter of Darwin’s, bearing upon pro- 
tective resemblance, has only recently been shown to me by my friend 
Professor E. B. Wilson, the great American Cytologist. With his kind 
1 More Letters, u, pp. 77, 78. 
2 More Letters, u. p. 62. See also Descent of Man, p. 261. 
3 More Letters, u. p. 95. 
