ae se Da DS aaa & a 
D.—ZOOLOGY. 85 
detailed resemblance to one out of many different appearances which the 
same object may present—e.g. to a leaf gnawed into a particular shape by 
a caterpillar—would often mean safety to a rare, hard-pressed species 
but great danger to a common one ; for the sharp senses of enemies would 
quickly detect the meaning of that one shape, and then a special search 
would be made for it.2® I am sure, however, that everyone will share the 
author’s hopes for further observations on the living insects in their natural 
surroundings. 
On the subject of the Protective Resemblance to leaves I cannot 
resist the temptation to say a few words about W. J. Kaye’s discovery 
of the part played by the dead-leaf-like under surface of the tropical 
American butterfly Protogonius.8° The upper side of this butterfly roughly 
resembles the conspicuous warning pattern of the predominant mimetic 
association of its locality, changing when the pattern changes as we pass 
from one area to another—always a mimic although always a poor one. 
At rest, with folded wings, the resemblance to a dead leaf is perfect. Now 
Kaye observed that when the open wings of these butterflies were seen from 
below against the sky the appearance was that of the upper surface, so that 
at first. he thought they must be flying upside down. When, however, he 
examined them he found that the apparently opaque dead-leaf-like 
under side was completely overwhelmed by the stronger contrasts of the 
upper surface. The wings of Protogonius were shown in this Section at 
Liverpool in 1923, when a friend who does not greatly favour an interpreta- 
tion based on Natural Selection, pointed out rather triumphantly that the 
dark and the light parts of the two patterns correspond respectively. But 
this is precisely the kind of result which affords proof of evolution by 
selection. The two patterns certainly have a common plan, but by 
stippling here, softening there, and the addition of delicate tints in streaks 
and washes, the conspicuous, strongly contrasted mimetic pattern of the 
upper surface is replaced on the under by a beautiful and detailed likeness 
to a dead leaf. 
Before considering the objections to the theory of mimicry it is 
necessary to devote a little time to Fritz Miiller’s interpretation of the 
resemblances which Bates was unable to explain. His difficulty was 
caused by the remarkably detailed likeness between many species in the 
two groups which he called Danaoid and Acreoid Heliconide, groups 
_teally widely separated and now known respectively as the Ithomune and 
Se at 
the Heliconine, both conspicuous and distasteful, and providing models 
for other butterflies and moths, yet often mimicking each other, the 
Helhiconine being commonly mimetic, the Ithomiine rarely. Bates was 
teferring to these resemblances in the following sentence: ‘Not only, 
however, are Heliconide [viz. both the Danaoid and Acreoid groups] the 
objects selected for imitation ; some of them are themselves the imitators ; 
in other words, they counterfeit each other, and this to a considerable 
extent.’* The theory of mimicry which bears Fritz Miiller’s name was 
* Proc. Ent. Soc. Lond., 1924, p. cxlv. 
9 [bid., 1922, p. xcviii ; 1923, p. xxxvii. See also p. xl for Lord Rayleigh’s notes 
_ on the optical interpretation. 
. 81 Jbid., p. 507. 
