Adjustment of colour in various pu'pa^, etc. 395 



These latter are also, though less transparent than the 

 green, chiefly so in the same area. 



The green pupae resemble green leaves and stems, and 

 Mr. Merrifield's experiments show that they are produced 

 by such surroundings : tlie hone-coloured pupse resemble, 

 and are produced by, such surfaces as bark, wood, or stone. 



Now the transpax'ency is no hindrance to the conceal- 

 ment of the former : it is rather an advantage. But to 

 the latter it is a distinct hindrance and, when once seen, 

 immediately betrays the fact that the pupa is not the 

 opaque object to which it presents so strong a superficial 

 resemblance. I believe that this is the reason why this 

 particular area is so invariably covered up by dark patches 

 of pigment in the pale bone-coloured pupse of this species. 

 I believe that the persistence of this particular mark 

 when the other pigment spots and masses are disappearing 

 in the palest pupse, is due to the operation of natural 

 selection. 



The experiments and observations Miss Cora B. 

 Sanders and I were able to conduct, in the summer of last 

 year, prove that pupaj (in this case of Vanessa urticm) are 

 subject to a tremendous struggle for life : they also 

 strongly indicate that the enemies are guided by their 

 sight in hunting for them. Hence it appears to me that 

 there is nothing improbable about the suggestion that this 

 dark patch covering the transparent area may have been 

 retained by natural selection in certain forms, because 

 transparency would be a danger, n)ay have been dismissed 

 in certain others, because transparency would be an 

 advantage. 



The pupae were compared and tabulated on Dec. 22nd, 

 1898, and on the following dates in 1899 — Jan. 6th, 7th, 

 9th, and 28th. Nearly all of them were extremely healthy, 

 and showed the effects of the conditions in a remarkable 

 manner. As these are the first complete and detailed ex- 

 periments which have been conducted upon this sensitive 

 species, and the' material was in such excellent condition, 

 the comparison was carried out with the utmost care, 

 and numerous details were recorded which are included 

 in the tabular statement below. The order is that in 

 which the pupse of P. machaon were considered so far as 

 the conditions were the same. The conditions which 

 were different are placed at the end. 



It is to be observed that the light-green forms (3 h) 



