60 
NATURAL SELECTION 
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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 Hcliconidse 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 Heliconidae ; — 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 Heliconidee 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 Heliconidee, and that it is therefore equally an 
