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Introduction ~~ xix 
f 
about by natural selection—the less perfect the mimicry 
the more liable are the individuals to be attacked, and the 
less chance have they of reproducing their kind. 
This imitation was first accounted for by Mr. Bates in 
the case of the Heliconide, a group of showy, slow-flying 
abundant butterflies possessing “‘a strong pungent semi- 
aromatic or medicinal odour which seems to pervade all 
the juices of their system.”’ It does not follow, of course, 
that what seems to us a disagreeably smelling fluid should 
prove distasteful to the palate of a lizard or a bird. But 
careful observation of the butterflies convinced both Bates 
and Wallace that they were avoided, or at any rate not 
pursued, by birds and other creatures; and Belt found 
that they were rejected by his tame monkey which was 
very fond of other insects. So their conspicuous wings, 
with spots and patches of yellow, red, or white upon a 
black, blue, or brown ground, may fairly be considered an 
example of warning colouration—though Mr. Thayer has 
with great ingenuity and acumen endeavoured to show 
that the markings are effective for concealment and 
that their value as warning marks is doubtful. Now, says 
Mr. Beddard, ‘‘ in the same situations as those in which the 
Heliconias are found there also occur, more rarely, speci- 
mens of butterflies minutely resembling the Heliconias, but 
belonging to a perfectly distinct family—the Pieride. 
They belong to the two genera Leptalis and Euterpe, con- 
sisting of numerous species, each of which shows a striking 
likeness to some one particular species of Heliconia. This 
likeness is not a mark of near affinity; it affects no im- 
portant character, but only the shape and colouration of 
the wings.”’ 
The particular resemblance here described was the origin 
of the theory of Protective Mimicry, the conditions under 
which it occurs being, according to Mr. Wallace: (1) That 
the imitative species occur in the same area and occupy 
the same station as the imitated. (2) That the imitators 
are always the more defenceless. (3) That the imitators 
are always less numerous in individuals. (4) That the 
imitators differ from the bulk of their allies. (5) That the 
imitation, however minute, is external and visible only, 
never extending to internal characters or to such as do not 
affect the external appearance. 
