68 



THE BRITISH NATURALIST. 



[April 



this insect, I have taken it on our dry sand-hills at Hartlepool, quite 

 as dark as the darkest in Mr. Tutt's lengthy series, and what is more, 

 we never by an} 7 chance take a light coloured one. 



With reference to this assumed change of view, it must be 

 remembered that the earlier portion had been written a year or two 

 before, and that as it had appeared, the question was being discussed 

 in his correspondence, and he was extending his remarks and enlarging 

 his views in consequence. But the clear and definite theory, that 

 melanism was the result of the westerly winds charged with moisture 

 from the Gulf Stream, is no longer put forward as the active agent it 

 was assumed to be at first, but moisture is now spoken of as an 

 indirect or secondary cause at most. Thus at p. 48 he refers again 

 to swampy climates, and says : " But if moisture is to be taken as a 

 direct, rather than an indirect cause, we should expect to find melanic 

 variation occurring in the swamps of Tropical Africa, in the Forests 

 of the Amazon, on the banks of the Mississippi, and in many other damp 

 climates, even within tropical regions, and I am not aware that this is 

 the case." And on the next page " Although I certainly look on 

 moisture as an indirect rather than a direct cause of melanism." 

 Still further to emphasize the point I wish to make, that the settled 

 opinions of the earlier pages, were settled no longer, he writes on p. 49 

 " Lord Walsingham's idea as to the action of the actinic rays of the 

 sun in producing colour, and the absorbtion of certain of these rays 

 by clouds, &c, as a probable cause of melanism, is quite new to me," 

 and after discussing this point, he says (p. 50) : "Although I thus still 

 venture to differ from Lord Walsingham, I must candidly confess 

 that his remarks have modified my previously formed opinions, and 

 that I should not now feel inclined to give the probable action of 

 sunlight such short shrift as I gave it in a previous paragraph." 



But though we find in this portion of the pamphlet an inclination to 

 retreat from the very decided views enunciated at the beginning, he 

 returns very much to his earlier opinion before he concludes. Letters 

 from Mr. Smith, of Ashburton, New Zealand, Mr. Cockerell, and 

 Dr. Chapman, are quoted in support of the moisture theory. It is not 

 possible for me to quote the passages, and I am quite aware that I am 

 laying myself open to the remark that what I do not reply to is left 

 over because it is unanswerable, but I knew when I undertook to read 

 this paper, that I could not possibly discuss every point at length. 

 In reference to these letters quoted by Mr. Tutt, I will observe only 

 that of Dr. Chapman, who is one of the most thoughtful and original 

 of all students of Lepidoptera, does not support the idea that moisture 

 produces melanism. His communication is a careful argument which, 

 on the assumption that " dark colouration is advantageous to a species 

 living in a damp and cold climate," shows how by natural selection 



