THE CATTSE OF MIMETIC RESEMBLANCE. 597 



the resemblance is never attained by precisely similar metbods, 

 and generally by metbods wbicb are extremely unlike. I propose, 

 in concluding tbis Section, to discuss a few examples from tbe 

 Lepidoptera, inasmuch as tbe resemblances in question have 

 been chiefly studied in this group, and because an explanation 

 based on the theory of external or on that of internal causes 

 has been sought more often and pressed more strongly in the 

 case of the Lepidoptera than in that of any other Order. 



The PierincB are specially liable to take on these resem- 

 blances. In tropical America they chiefly resemble the Itho- 

 miinee, Heliconince, and Papilionince, affording some of the best 

 and earliest recorded examples of mimicry (although Dr. F. A. 

 Dixey has now shown that they are more probably to be inter- 

 preted as common warning colours). The chemical nature of 

 the wing-pigments of the Pierince has recently formed the 

 subject of an interesting paper by F. Gowland Hopkins (Proc. 

 Eoy. Soc. 1894, p. 5, and Phil. Trans. 1895, B. p. 661). The 

 author shows that the white pigment so common in the group 

 is an impure uric acid probably uncombiued, that the yellow and 

 orange pigment is a derivative of uric acid to which he gives the 

 name "lepidotic acid," while a much rarer red pigment, less 

 fully investigated, is probably of a closely similar constitution. 

 These three pigments, with black, which is apparently intimately 

 associated with the cuticle of the scales, with a pigment placed 

 between the two laminae of the wing and with superadded 

 optical effects due to structure, account for the whole of the 

 colouring of Pierine butterflies. No pigment of similar consti- 

 tution to the Pierine white, yellow, and red, was found by 

 Mr. Hopkins in any other butterfly — not even in the allied 

 PapilionincB. The Pierine butterflies which resemble the Itlio- 

 miinae or other butterflies were found by Mr. Hopkins to achieve 

 this end, not by gaining the true pigments of their models, 

 but by means of the characteristic Pierine pigments. The 

 bands of warm red-brown, the spots of white and yellow, which 

 so closely resemble the same tints in the IthomiincB, are in 

 reality caused by pigments of an entirely different' nature — the 

 resemblance, even between the pigments themselves, is wholly 

 superficial. 



The argument that the resemblances we are discussing are 

 due to the common result of common forces, is simply an 

 improbable assumption. It has been proved again and again 



