Ch^p. XI. Butterflies and Moths. 323 



the sexes mostly depending on the form of inheritance which 

 has prevailed. Inheritance is governed hy so many unknown 

 laws or conditions, that it seems to us to act in a capricious 

 manner ;'^ aiid we can thus, to a certain extent, understand how 

 it is that with closely allied species the sexes either differ to an 

 astonishing degree, or are identical in colour. As all the suc- 

 cessive steps in the process of variation are necessarily trans- 

 mitted through the female, a greater or less number of such 

 steps might readily become developed in her ; and thus we can 

 understand the frequent gradations from an extreme difference 

 to none at all between the sexes of allied species. These cases of 

 gradation, it may be added, are much too common to favour the 

 supposition that we here see females actually undergoing the 

 process of transition and losing their brightness for the sake of 

 protection ; for we have every reason to conclude that at any 

 one time the greater number of species are in a fixed condition. 



Mimicry. — This principle was first made clear in an admirable 

 paper by Mr. Bates,^' who thus threw a flood of light on many 

 obscure problems. It had previously been observed that certain 

 butterflies in S. America belonging to quite distinct families, 

 resembled the Heliconidas so closely in every stripe and shade of 

 colour, that they could not be distinguished save by an ex- 

 perienced entomologist. As the Heliconidse are coloured in 

 their usual manner, whilst the others depart from the usnal 

 colouring of the groups to which they belong, it is clear that 

 the latter are the imitators, and the Heliconidas the imitated. 

 Mr. Bates further observed that the imitating species are com- 

 paratively rare, whilst the imitated abound, and that the two 

 sets live mingled together. From the fact of 'the HeliconidsB 

 being conspicuous and beautiful insects, yet so numerous in 

 individuals and species, he concluded that they must be pro- 

 tected from the attacks of enemies by some secretion or odour ; 

 and this conclusion has now been amply confirmed,'" especially 

 by Mr. Belt. Hence Mr. Bates inferred that the butterflies 

 which imitate the protected species have acquired their present 

 marvellously deceptive appearance through variation and natural 

 selection, in order to be mistaken for the protected kinds, and 

 tlius to escape being devoured No explanation is here attempted 

 of the brilliant colours of the imitated, but only of the imitating 

 butterflies. We must account for the colours of the former in 

 the same general manner, as in the cases previously discussed 



* ' The Variation of Animals and xxiii. 18R2, p. 495. 



Plants under Domestication,' vol. ii. '" ' Proc. Ent. Soc' Dec. 3ii\ 



map. xii. p. 17. 1866, p. xlv. 



^° ' Transact. I.inn. Soc' toI. 



