OF THE AMAZON VALLEY. 507 



Bees, Wasps, and other Hymenopterous and Dipterous insects. The parallelism between 

 these several forms and their geographical relations have not yet, I believe, been inves- 

 tigated. The resemblances seem to be more closely specific in tropical countries than 

 in Europe ; and I think it likely that the counterfeits in high latitudes may not always be 

 found in company with their models. It is possible the geographical relations between 

 the species concerned may have been disturbed by the great climatal and geological 

 changes which have occurred in this part of the world since the date when they first 

 came into existence. 



Not only, however, are Helicomdce 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. Species belonging to distinct genera have been confounded, owing 

 to their being almost identical in colours and markings ; in fact, many of them can 

 scarcely be distinguished except by their generic characters. It is a most strange cir- 

 cumstance connected with this family, that its two sections, or subfamilies, have been 

 mingled together by all authors, owing to the very close resemblance of many of their 

 species. Analogies between the two subfamilies have been mistaken for affinities. It is 

 sometimes difficult to understand in these cases which is the imitator and which the 

 imitated. We have, however, generally a sure test in the one set exhibiting a departure 

 from the normal style of colouring of their congeners, whilst the other are conformable 

 to their generic types. The species of Napeogenes are, by this criterion, evidently aU 

 imitators of Itliomics; they are also rare insects, like the Leptalkles. The mimetic 

 species of Helieonius must be, for the same reason, imitators. 



These imitative resemblances, of which hundreds of instances could be cited, are full 

 of interest, and fill us with the greater astonishment the closer we investigate them ; for 

 some show a minute and palpably intentional Likeness which is perfectly staggering. I 

 have found that those features of the portrait are most attended to by nature which pro- 

 duce the most effective deception when the insects are seen in nature. The faithfulness 

 of the resemblance, in many cases, is not so striking when they are seen in the 

 cabinet. Although I had daily practice in insect-collecting for many years, and was 

 always on my guard, I was constantly being deceived by them when in the woods. It 

 may be asked, why are mimetic analogies so numerous and amazingly exact in insects, 

 whilst so rare and vague in the higher animals* ? The only answer that I can suggest 

 is, that insects have perhaps attained a higher degree of specialization, after their type, 

 than most other classes : this seems to be shown by the perfection of their adaptive 

 structures and instincts. Their being more numerous and striking in tropical than in 

 temperate countries is perhaps attributable to the more active competitive life, and the 

 more rapid succession of their generations, in hot than in cold countries. 



It is not di£Q.cult to divine the meaning or final cause of these analogies. When we 



* Two instances of mimicry in birds, quite as wonderful as those between LeptaUs and Ithomia, have just been 

 communicated to me by my old travelling companion, Mr. A. R. Wallace. He has observed two species of OnoUdce 

 (perverted from the normal facies of the family) attendant on two species of Meliphagidai, and mimicking them in the 

 most curiously minute way in colours and in general figure. The associated pairs inhabit separate islands, as follows : — 

 — L Bourou, Mimeta {Oriolidai) Boiiro'insis, Tropidorhynchus {Meliphagidce), n. sp. ; L Ceram, Mimeta Forstini, 

 Tropidorhynchus suhcarinatus. 



