332 THE ZOOLOGIST. 



instances cited by Mr. Distant are quite inappropriate as illustrations of 

 his fundamental suggestions, though possibly they might be brought 

 forward in support of a theory that assimilative colouration has been 

 sporadically developed from recent geological times down to the present day. 



On glancing through the quotations given, one is at once struck by the 

 practically complete absence of anything in the way of experimental evidence 

 as to the direct action of the environment, and this is the more strange 

 seeing that such evidence is actually available. It will be sufficient to refer 

 to the splendid series of exhaustive experiments made by Prof. Poulton 

 upon the influence of both food and surrounding colours on the larvae and 

 pupae of various Lepidoptera. These experiments have been carried out 

 with the most scrupulous care and exactitude, and the conclusions which 

 can be drawn from them are worth scores of hasty observations and 

 occasionally inaccurate generalizations made by travellers and sportsmen. 

 It would be beside the point to enter into details as to the results obtained 

 by Prof. Poulton, since we are only discussiug the possibility of the 

 survival of primaeval assimilation ; but it may be mentioned that these 

 experiments definitely prove that certain of these organisms possess, in 

 varying degrees, the capacity of being modified in colour by the direct 

 action of different light-waves ; and, further, I consider it is sufficiently 

 demonstrated that this capacity can only be satisfactorily explained by the 

 theory of natural selection, and not by any theory of purely internal or 

 external causes. 



But to resume: with reference to the attempt to explain the crimson 

 colour in the wings of the African Touracos (Turacus and Gallirex) as 

 being due to the occurrence of coppeHn the districts which they frequent, 

 I quite agree with the objections raised by Dr. Bovvdler Sharpe.* In my 

 experience of these beautiful birds, both in Natal and Mashonaland, I can 

 find no connection between their distribution and the occurrence of coppers ; 

 and besides, the fact, noted by Mr. Distant, that they have been known to 

 moult several times in captivity in England without impairing the brilliancy 

 of their feathers, appears to entirely negative any such direct connection. 

 Moreover, no attempt is made to explain why it is only these birds which 

 are affected in this curious way ; or why, in them, the effects are confined 

 to a limited number of feathers. 



It is noticeable that wherever phenomeua are explained upon the theory 

 of natural selection a detailed explanation of the " why and wherefore " is 

 always expected, whereas exponents of theories of purely environmental 

 causes are so frequently content to confine themselves to the widest of 

 generalities. 



* Dr. Sharpe's objections are given on the page criticized, and given as 

 a qualitative contradiction, — Ep. 



