xxrv.] NATUEAL SELECTION. 325 



same region ; we never find an imitator living remote from 

 the form which it counterfeits. The mockers are almost 

 invariably rare insects ; the mocked in almost every case 

 abound in swarms. In the same district in which a species 

 of leptalis closely imitates an ithomia, there are sometimes 

 other lepidoptera mimicking the same ithomia ; so that in 

 the same place, species of three genera of butterflies and 

 even moths may be found, all closely resembling a species 

 of a fourth genus. It deserves especial notice, that many 

 of the mimicking forms of the leptalis, as well as of the 

 mimicked forms, can be shown, by a graduated series, to 

 be merely varieties of the same species ; whilst others are 

 midoubtedly distinct species. But why, it may be asked, 

 are certain forms treated as the mimicked, and the others 

 as the mimickers ? Mr. Bates satisfactorily answers this 

 question, by showing that the form which is imitated 

 keeps the usual dress of the group to which it belongs, 

 whilst the counterfeiters have changed their dress, and do 

 not resemble their nearest allies." ^ 



The purpose of mimicry is the protection of the Its pnr- 

 mimickers. The species which they mimic, probably in protection, 

 consequence of some odour that they emit, are not preyed 

 on by birds ; and of course it is a protection to the butter- 

 flies which do not emit any such odour, to be mistaken for 

 those which do. The mimicking forms have no doubt its cause 

 been produced by the survival, through successive genera- selection.^ 

 tions, of those individuals belonging to defenceless species, 

 which most nearly resembled the kinds that have natural 

 means of protection. For the same reason, insects that 

 sting are never known to mimic others, though others 

 sometimes mimic them.^ 



1 Danvin's Origin of Species, p. 503. ^ Ibid. p. 606. 



