CLASSIFICATION 233 



iience they must suffer babituall}^ from some danger, for 

 otherwise, from the number of eggs laid bj all butter- 

 flies, they would in three or four generations swarm over 

 the whole country. Now if a member of one of these 

 persecuted and rare groups were to assume a dress so 

 like that of a well-protected species that it continually 

 deceived the practiced eyes of an entomologist, it would 

 often deceive predaceous birds and insects, and thus often 

 escape destruction. Mr. Bates may almost be said to 

 have actually witnessed the process by which the mimick- 

 ers have come so closely to resemble the mimicked; for 

 he found that some of the forms of Leptalis 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 common 

 Ithomia of the same district. In another district there 

 were two or three varieties, one of which was much com- 

 moner than the others, and this closely mocked another 

 form of Ithomia. From facts of this nature, Mr. Bates 

 concludes that the Leptalis first varies; and when a 

 variety happens to resemble in some degree any common 

 butterfly inhabiting the same district, this variety, from 

 its resemblance to a flourishing and little -persecuted 

 kind, has a better chance of escaping destruction from 

 predaceous birds and insects, and is consequently oftener 

 preserved — "the less perfect degrees of resemblance 

 being generation after generation eliminated, and only 

 the others left to propagate their kind." So that here 

 we have an excellent illustration of natural selection. 

 Messrs. Wallace and Trimen have likewise described 

 ■l several equally striking cases of imitation in the Lepidop 

 tera of the Malay Archipelago and Africa, and with 



