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 Volucella 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 



