12 MIMICRY— [CH. 



them especially liable to attack. If, however, they 

 could exchange their normal dress for one resembling 

 that of the Ithomiines it is clear that they would have 

 a chance of being mistaken for the latter and con- 

 sequently of being left alone. Moreover, in certain 

 cases these Pierines have managed to discard their 

 normal dress and assume that of the Ithomiines. On 

 theoretical grounds this must clearly be of advantage 

 to them, and being so might conceivably have arisen 

 tln?ough the operation of natural selection. This 

 indeed is what is supposed to have taken place on the 

 theory of mimicry. Those Pierines which exhibited 

 a variation of colour in the direction of the Ithomiine 

 "model" excited distrust in the minds of would-be 

 devourers, who had learned from experience to associate 

 that particular type of coloration with a disagreeable 

 taste. Such Pierines would therefore have a rather 

 better chance of surviving and of leaving offspring. 

 Some of the offspring would exhibit the variation in 

 a more marked degree and these again would in con- 

 sequence have a yet better chance of surviving. 

 Natural selection would encourage those varying in 

 the direction of the Ithomiine model at the expense of 

 the rest and by its continuous operation there would 

 gradually be built up those beautiful cases of resem- 

 blance which have excited the admiration of naturalists. 

 Wallace was the next after Bates to interest 

 himself in mimicry and, from his study of the butterflies 

 of the Oriental region^, shewed that in this part of 



1 Trans. Linn. Soc. vol. 25, 1866. 



