224 CLASSIFICATION. [Chap. XIV. 



and insects, and thus often escape 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 Leptalis which mimic so many other butter- 

 flies, varied in an extreme degree. In one district sev- 

 eral 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 commoner 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 inhabit- 

 ing the same district, this variety, from its resem- 

 blance 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 resem- 

 blance being generation cfter 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 

 several equally striking cases of imitation in the Lepi- 

 doptera of the Malay Archipelago and Africa, and with 

 some other insects. Mr. Wallace has also detected one 

 such case with birds, but we have none with the larger 

 quadrupeds. The much greater frequency of imitation 

 with insects than with other animals, is probably the 

 consequence of their small size; insects cannot defend 

 themselves, excepting indeed the kinds furnished with 

 a string, and I have never heard of an instance of 



