54 
NATURAL SELECTION 
in 
now merely necessary to show that concealment by obscure 
or imitative tints is only one out of very many ways by which 
animals maintain their existence ; and having done this we 
are prepared to consider the phenomena of what has been 
termed “ mimicry.” It is to be particularly observed, how- 
ever, that the word is not here used in the sense of voluntary 
imitation, but to imply a particular kind of resemblance — 
a resemblance not in internal structure but in external 
appearance — a resemblance in those parts only that catch 
the eye — a resemblance that deceives. As this kind of 
resemblance has the same effect as voluntary imitation or 
mimicry, and as we have no word that expresses the required 
meaning, “ mimicry ” was adopted by Mr. Bates (who was the 
first to explain the facts), and has led to some misunder- 
standing; but there need be none, if it is remembered 
that both “ mimicry ” and “ imitation ” are used in a meta- 
phorical sense, as implying that close external likeness which 
causes things unlike in structure to be mistaken for each 
other. 
Mimicry 
It has been long known to entomologists that certain 
insects bear a strange external resemblance to others belong- 
ing to distinct genera, families, or even orders, and with 
which they have no real affinity whatever. The fact, how- 
ever, appears to have been generally considered as dependent 
upon some unknown law of “analogy” — some “system of 
nature,” or “ general plan,” which had guided the Creator in 
designing the myriads of insect forms, and which we could 
never hope to understand. In only one case does it appear 
that the resemblance was thought to be useful, and to have 
been designed as a means to a definite and intelligible pur- 
pose. The flies of the genus Yolucella enter the nests of bees 
to deposit their eggs, so that their larvae may feed upon the 
larvae of the bees, and these flies are each wonderfully like 
the bee on which it is parasitic. Kirby and Spence believed 
that this resemblance or “ mimicry ” was for the express pur- 
pose of protecting the flies from the attacks of the bees, and 
the connection is so evident that it was hardly possible to 
avoid this conclusion. The resemblance, however, of moths 
