20 



it appears likely that many observations will be made by different 

 people. 



Notwithstanding the very complete review of the whole of the 

 possible causes of mimetic resemblance, as given by Professor 

 Poulton in the "Journal of the Linntean Society" for 1898 (Nat. 

 Select, the Cause of Mimetic Eesenib. and Common Warn. Col.), 

 there are still a large number of Entomologists who entertain doubt 

 as to the truths of mimicry at all. I will say here at once that I think 

 it is rather a pity that Professor Poulton's paper Avas not pnljlished 

 in a wholly entomological publication. It is certain that very many 

 entomologists have never even yet seen that comprehensive and 

 exhaustive paper, while a careful perusal of its pages, if one only 

 starts with a perfectly open mind, leaves one forced either to accept 

 Natural Selection as the cause of mimetic resemblance or to have 

 no explanation at all. One can even go so far as to state that those 

 who deny the truths of mimicry deny the truth of Natural 

 Selection. One of the commonest criticisms of mimicry is that the 

 same conditions of climate, etc., produce the same results, and that 

 two or more insects may evolve a pattern independently of one 

 another. One of the most negativing answers to this was shown 

 by Prof. Poulton to be the historical case of the two mimetic 

 Ithomiines, Methona covfiisa and Thyridia psidii, first noted by Bates 

 in the Amazon valley. These two transparent and black butterflies 

 of the same family, but of different genera, were examined micro- 

 scopically and were found to have been given a transparent appear- 

 ance in a different way. Both species, in common with all 

 Ithomiines, have two kinds of scales, usually one kind much 

 broader and shorter than the other. The Methona confiii^a was 

 foiind to have the long scales reduced to hairs and the broad scales 

 much reduced in size and shape. The Thi/ridia psidii was found to 

 have the long scales reduced but not to hairs, and the broad scales 

 reduced but retaining their original shape far more than the 

 Methona. Many other species of various families were examined 

 and the arrangement and nature of the scales was found to be 

 very different. In some the scales were set on edge so that 

 the light passed between them as in C'ast7iia linus. In others the 

 scales are fiat, but quite transparent, as in the Hypsid Moth of the 

 genus Anthfntujza. In others the scales are quite normal, except 

 that they are greatly reduced in number, so that light passed 

 between them. To say here that similar conditions of climate 

 produce similar results, is simply an untruth, for if climate can 

 make one species lose a number of its scales, it should act in the 



