PDF - Wallace Online

54 NATURAL SELECTION innow merely necessary to show that concealment by obscureor imitative tints is only one out of very many ways by whichanimals maintain their existence ;and having done this weare prepared to consider the phenomena of what has beentermed "mimicry." It is to be particularly observed, however,that the word is not here used in the sense of voluntaryimitation, but to imply a particular kind of resemblancea resemblance not in internal structure but in externalappearance a resemblance in those parts only that catchthe eye a resemblance that deceives. As this kind ofresemblance has the same effect as voluntary imitation ormimicry, and as we have no word that expresses the requiredmeaning, " mimicry " was adopted by Mr. Bates (who was thefirst to explain the facts),and has led to some misunderstanding;but there need be none, if it is rememberedthat both " mimicry " and " imitation " are used in a metaphoricalsense, as implying that close external likeness whichcauses things unlike in structure to be mistaken for eachother.MimicryIt has been long known to entomologists that certaininsects bear a strange external resemblance to others belongingto distinct genera, families, or even orders, and withwhich they have no real affinity whatever. The fact, however,appears to have been generally considered as dependentupon some unknown law of "analogy" some "system ofnature," or " general plan," which had guided the Creator indesigning the myriads of insect forms, and which we couldnever hope to understand. In only one case does it appearthat the resemblance was thought to be useful, and to havebeen designed as a means to a definite and intelligible purpose.The flies of the genus Volucella enter the nests of beesto deposit their eggs, so that their larvae may feed upon thelarvae of the bees, and these flies are each wonderfully likethe bee on which it is parasitic. Kirby and Spence believedthat this resemblance or " mimicry " was for the express purposeof protecting the flies from the attacks of the bees, andthe connection is so evident that it was hardly possible toavoid this conclusion. The resemblance, however, of moths