Chap. XIII. ANALOGICAL EESEMBLANCES. 385 



p^emis. It deserves especial notice that many of the mimick- 

 inn^ forms of the Lcptalis, as ■well as of the mimicked forms, 

 can be shown hy a g^raduated series to be merely varieties of 

 the same species ; while others are undoubtedly distinct spe- 

 cies. But why, it may be asked, are certain Jbrms treated as 

 tlie mimicked and othei's as tlic mimickers ? Mr. Bates satis- 

 factorily answers this question, by showing);' that the form 

 Avliicli is imitated keeps the usual dress of the f^roup to which 

 it lielongs, while the counterfeiters have changed their dress 

 and do not resemble their nearest allies. 



^\'e are next led to inquire what reason can possibly be as- 

 signed for certain butterflies and moths so often assuming the 

 dress of another and quite distinct form ; why, to the perplexity 

 of naturalists, has Nature condescended to the tricks of the 

 stage? ]Mr. Bates has, no doubt, hit on the true explanation. 

 The mocked forms, wliich always aboimd in numbers, nuist 

 habitually escape destruction to a large extent, otherwise they 

 could not exist in such swarms ; and Mr. Bates never saw 

 them preyed on l)y birds and certain large insects which at- 

 tack other butterllies. He has good reason to believe that 

 this innnunity is owing to a peculiar and offensive odor which 

 they emit. The mocking forms, on the other hand, that in- 

 habit the same district, are comparatively rare, and belong to 

 lare groups ; hence they must suffer habitually from some 

 danger, A^r otherwise, from the number of eggs laid bv all but- 

 terflies, they would in three or four generations swarm over the 

 wliole country. Now if a member of one of these persecuted 

 and rare groups were to assume a dress so like that of a well- 

 ])rotected species that it continually deceived the practised 

 eyes of an entom(ilogist, it would often deceive predacious birds 

 and insects, and thus escape much destruction. Mr. Bates 

 may almost be said to have actually witnessed the process 

 by which the mimickers have come so closely to resemble the 

 mimicked ; for he found that some of the forms of Lcptalis 

 which mimic so many other butterflies, varied in an extreme 

 degree. In one district several varieties occurred, and of these 

 one alone resembled, to a certain extent, the conunon Ithomia 

 of the same district. In another district there were two or 

 three varieties, one of which was much commoner than the 

 others, and this closely mocked another form of Ithomia. 

 From facts^of this nature, Mr. Bates concludes that the I^op- 

 talis first varies ; and when a variety hajipens to resemble in 

 some degree any common butterfly inhabiting the same district, 

 17 



