OF THE AMAZON VALLKY. 511 



privecl of them. It is not unreasonal)lo to suppose that some species are taken l)v in- 

 sectivorous animals, Avhilst otliers tlyiuii,- in company Avith them arc avoided. 1 (;ould 

 not, from their excessive scarcity, ascertain on the spot that the Lcptulides were thus 

 picked out. I noticed, liowever, that other i^enera of tlunr family {Pieri(hi') were mucli 

 persecuted. AVe have proof, in the case of Sand-AVasj)s, whicii ))rovision their nests 

 with insects, that a single species is very I'rnerally selected ont of numhcrs, even of the 

 same yenus, existing in the same locality. 1 was quite convinced in the c-ase of Ccrccria 

 binodis of South America, which destroys numbers oi a ^legalostoui is {hxmWy Cli/lhridcr), 

 that the great rarity of the ]5eetle was owing to its serving as prey to the Ccrccrin. A\'e 

 cannot point out all the conditions of life of each species concerned in these mimetic 

 analogies. All tliat we can say is, that some species show, hy their great abundanci; in 

 the adult state, that during this period, before they propagate their kind, they enjov bv 

 some means imnumity from eif(>ctive persecution, ami that it is tlu'refore an advantage 

 to others 7iot so fortunate, and otherwise unprovided for, if they are so like as to be 

 mistaken for them. 



The 2:)rocess by which a mimetic analogy is l)rouglit about in nature is a prol)leTn 

 which involves that of the origin of all species and all adaptations. What I have pre- 

 viously said rc'garding the variation of species, and the segr{!gation of local rac-es from 

 variations, the change of species of Heliconidce from one locality to another, and the 

 probable vital necessity of their counterfeits which accompany them keeping to the 

 exact imitation in each locality, has prepared the way to the explanation I have to give. 

 In the eases of local variation of the Ilclicoiiidci', there was nothing, as before remarked, 

 very apparent in the conditions of the localities to show why one or more of the varieties 

 should prevail in each over their kindred varieties. There was nothing to show plainly 

 that any cause of the formation of local varieties existed, other than tlie direct action of 

 physical coiulitions on the iiulividuals, altiiough this might be seen to be clearlv incom- 

 petent to exj)lain the oceurrenc(> (jf several varieties of tiie same species in one locality. 

 "VVe could only conclude, from the way in which the varieties occur in nature, as described 

 in the case of JlcrhiniUis Pohniinid, that the local conditions favoured the increase of one 

 or more varieties in a district at the expense of the others — the selected ones being 

 diflerent in different districts. "What these conditions were, or have been, was not revealed 

 by the facts. AA'ith the mimetic species Lcplalis Theono'e the case is different. "We sec 

 here a similar segregation of local forms to tliat of Mechanitis Foli/intiia ; l)ut we believe 

 w(.' know the conditions of life of the species, and find that they vary from one locality to 

 another. The existence of the species, in each locality, is seen to depend on its form and 

 colours, or drcsti, being assimilated to those of the I//io)tii(C of the same district, Mhich 

 Ithoiii'uc are changed from place to place, such assimilation being apparently its only 

 means of escai)ing extermination by insectivorous animals. Thus we havc> here the 

 reason why local races are formed out of the natural variations of a species: the (piestion 

 then remains, how is this brought al)out !- 



The explanation of this seems to be (piit(> clear on the theory of natural selection, as 

 recently expounded l)y Mr. Darw in in the ' Origin of Species.' The local varieties or 

 races cannot be supposed to have been formed by the direct action of physical conditions 



VOL. xxiii. 3 z 



