262 THEORIES OF MIMICRY 



resemblance is a direct effect of climatic or other forces 

 connected with locality, when the results are in reality so 

 utterly different and yet superficially so entirely alike. 

 It is obvious that the methods by which the appearance 

 of a terminal thickening is produced in "the two mimics 

 are as essentially different as are those by which the 

 appearance of short antennae is produced in the model 

 on the one hand, and its two mimics on the other. The 

 fact which requires explanation is the extraordinary like- 

 ness in spite of the essential difference, and this, when it 

 is repeated again and again, cannot be interpreted by any 

 theory unless based upon the principle of selection. 



Many other examples of the same kind could easily be 

 brought forward : in fact, it may be admitted as a general 

 principle that in Protective Mimicry and Common Warn- 

 ing Colours the resemblance is never attained by precisely 

 similar methods, and generally by methods which are 

 extremely unlike. I propose, in concluding this Section, 

 to discuss a few examples from the Lepidoptera, inasmuch 

 as the 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 

 Mimetic Lepidoptera than in any other Order. 



The Pierinae are specially liable to take on these 

 Resemblances. In tropical America they chiefly resemble 

 the Ithomiinae, Heliconinae, and Papilioninae, 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 interpreted as Common 

 Warning Colours). The chemical nature of the wing- 

 pigments of the Pierinae has recently formed the subject 

 of an interesting paper by F. Gowland Hopkins. 1 The 

 author shows that the white pigment so common in the 

 group is an impure uric acid probably uncombined, 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 



1 Proc. Roy. Soc, lvii, 1894, p. 5, and Phil. Trans., 1895, B. p. 661. 



