ANALOGICAL RESEMBLANCES. 417 



they are distasteful to birds and other insect-devouring ani- 

 mals. The mocking forms, on the other hand, that inhabit 

 the same district, are comparatively rare, and belong to rare 

 groups ; hence, they must suffer habitually from some danger, 

 for otherwise, from the number of eggs laid by 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 practised 

 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 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 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 resemblance being generation after gen- 

 eration 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 sev- 

 eral equally striking cases of imitation in the Lepidoptera 

 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 sting, and I have never heard of an 

 instance of such kinds mocking other insects, though they 

 are mocked ; insects cannot easily escape by flight from the 

 larger animals which prey on them ; therefore, speaking 

 metaphorically, they are reduced, like most weak creatures, 

 to trickery and dissimulation^ 



