282 THE entomologist's record. 



countries with high temperatures. In short, the " cold " 

 theory of melanism can only be maintained or bolstered up by 

 finding different explanations for almost every different case. 

 I have no doubt, that, if Mr. Merrifield's attention had been 

 directed to humidity as a cause of darkening, my own ideas of 

 melanism would have received substantial corroboration. I 

 think no better proof of the small effect " cold " can have in 

 darkening colour, could be produced than Mr. Merrifield's 

 remarks on " icing." He writes of some moths, produced from 

 pupae iced for a considerable time : — ■" The cooling in this case 

 not produce any change of colour, or, if any, it is a very slight did 

 one." Again, about another experiment, Mr. Merrifield (p. 93) 

 writes: — "The later ones of the 8 are very much darker 

 than the earlier ones, and, though the progressive darkening 

 is not quite regular, it is difficult to look at them without think- 

 ing that retardation of development has been the operative 

 cause, t/ie retardation in this case not being associated zvith cold, 

 as the pupae have rarely or never been at a lower temperature 

 than ^Qp. There are some other facts which rather favour the 

 view that retardation, without cold, may be a cause of, or at 

 least be associated with, darkening," etc. ; and again (p. 94), 

 " there is no marked difference (in colour) between those which 

 have been frosted and the rest." What a pity it seems that 

 Mr. Merrifield's attention had not been directed to the inci- 

 dental circumstance of " humidity," as some most valuable 

 results would undoubtedly have been obtained. 



Lord Walsingham's paper on Melanism, which has attracted 

 some attention, is also based on temperature. His paper can 

 hardly be said to propound a theory, as it scarcely seeks to 

 show what is the cause of melanism, but that, melanism once 

 having been produced, the dark coloration is an advantage to 

 the insect possessing it ; it then goes on to suggest that this 

 advantage, therefore, is the cause of the insect being melanic ; 

 although, how it can in any way be looked upon as a " cause " 

 of melanism, I fail entirely to see. But we have to bear in 

 mind that, although the whole of Lord Walsingham's theory (?) 

 {Presidential Address to the Yorkshire Naturalists' Society, 

 1885) that melanism is probably due to the rapidity with 

 which the insects would absorb heat because of their darker 

 coloration, is extremely interesting and full of good reasoning, 

 yet it is entirely misleading, because based on entirely fallacious 

 data. The assumption, that insects from high latitudes are 

 generally melanic, is entirely erroneous. They appear to be 



