NATURAL SELECTION 



verse bands ; while the delicate Ithomias are all more or less 

 transparent, with black veins and borders, and often with 

 marginal and transverse bands of orange red. These different 

 forms are all copied by the various species of Leptalis, every 

 band and spot and tint of colour, and the various degrees of 

 transparency, being exactly reproduced. As if to derive all 

 the benefit possible from this protective mimicry, the habits 

 have become so modified that the Leptalides generally 

 frequent the very same spots as their models, and have the 

 same mode of flight ; and as they are always very scarce 

 (Mr. Bates estimating their numbers at about one to a 

 thousand of the group they resemble), there is hardly a 

 possibility of their being found out by their enemies. It is 

 also very remarkable that in almost every case the particular 

 Ithomias and other species of Heliconidse which they resemble 

 are noted as being very common species, swarming in indi- 

 viduals, and found over a wide range of country. This 

 indicates antiquity and permanence in the species, and is 

 exactly the condition most essential both to aid in the 

 development of the resemblance and to increase its utility. 



But the Leptalides are not the only insects who have 

 prolonged their existence by imitating the great protected 

 group of Heliconidse; a genus of quite another family of 

 most lovely small American butterflies, the Erycinidse, and 

 three genera of diurnal moths, also present species which 

 often mimic the same dominant forms, so that some, as 

 Ithomia ilerdina of St. Paulo, for instance, have flying with 

 them a few individuals of three widely different insects, 

 which are yet disguised with exactly the same form, colour, 

 and markings, so as to be quite undistinguishable when upon 

 the wing. Again, the Heliconidse are not the only group 

 that are imitated, although they are the most frequent models. 

 The black and red group of South American Papilios, and 

 the handsome Erycinian genus Stalachtis, have also a few 

 who copy them ; but this fact offers no difficulty, since these 

 two groups are almost as dominant as the Heliconidse. They 

 both fly very slowly, they are both conspicuously coloured, 

 and they both abound in individuals ; so that there is every 

 reason to believe that they possess a protection of a similar 

 kind to the Heliconidae, and that it is therefore equally an 



