PDF - Wallace Online

in PROTECTIVE RESEMBLANCES AMONG ANIMALS 59many cases be sufficient for it to lay a quantity of eggs andleave a numerous progeny, many of which would inheritthe peculiarity which had been the safeguard of their parent.Now, this hypothetical case is exactly realised in SouthAmerica. Among the white butterflies forming the familyPieridse (many of which do not greatly differ in appearancefrom our own cabbage butterflies)is a genus of rather smallsize (Leptalis), some species of which are white like theirallies, while the larger number exactly resemble the Heliconidsein the form and colouring of the wings. It mustalways be remembered that these two families are as absolutelydistinguished from each other by structural characters as arethe carnivora and the ruminants among quadrupeds, and thatan entomologist can always distinguish the one from theother by the structure of the feet, just as certainly as azoologist can tell a bear from a buffalo by the skull or by atooth. Yet the resemblance of a species of the one family toanother species in the other family was often so great, thatboth Mr. Bates and myself were many times deceived at thetime of capture, and did not discover the distinctness of thetwo insects till a closer examination detected their essentialdifferences. During his residence of eleven years in theAmazon valley, Mr. Bates found a number of species orvarieties of Leptalis, each of which was a more or less exactcopy of one of the Heliconidse of the district it inhabited ;and the results of his observations are embodied in a paperpublished in the Linncean Transactions, in which he first explainedthe phenomena of " mimicry " as the result of naturalselection, and showed its identity in cause and purpose withprotective resemblance to vegetable or inorganic forms.The imitation of the Heliconidae by the Leptalides iscarried out to a wonderful degree in form as well as incolouring. The wings have become elongated to the sameextent, and the antennae and abdomen have both becomelengthened, to correspond with the unusual condition inwhich they exist in the former family. In coloration thereare several types in the different genera of Heliconidae. Thegenus Mechanitis is generally of a rich semi-transparentbrown, banded with black and yellow ;Methona is of largesize, the wings transparent like horn, and with black trans-