Chap. XIV.] ANALOGICAL RESEMBLANCES. 377 



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 pre- 

 daceous 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 resemblance to 

 a nourishing 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 re- 

 semblance 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 Triinen 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 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 ani- 

 mals which prey on them ; therefore, speaking metaphorically, they 

 are reduced, like most weak creatures, to trickery and dissimulation. 



It should be observed that the process of imitation probably never 

 commenced between forms widely dissimilar in colour. But starting 

 with species already somewhat like each other, the closest resem- 

 blance, if beneficial, could readily be gained by the above means ; 

 and if the imitated form was subsequently and gradually modified 

 through any agency, the imitating form would be led along the 

 same track, and thus be altered to almost any extent, so that it 

 might ultimately assume an appearance or colouring wholly unlike 



