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 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 

 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 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 

 several equally striking cases of imitation in the 

 Lepidoptera of the Malay Archipelago and Africa, and 

 with some other insects. Mr. Wallace has also de- 

 tected one such case with birds, but we have none 

 with the larger quadrupeds. The much greater fre- 

 quency 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 sting, and I have 



