The Zoologist — February, 1867. 575 



Wcstwood bad urged against the explanation of these imitative analogies on Darwinian 

 principles. He said that the case of the Leptalides published by him could not, in 

 his opinion, be explained iu any other way. The species of Leptalis in question was 

 found in several distant localities ; in some of them it existed under one constant 

 local form only, in others it was exceedingly variable, the common varieties showing a 

 wonderful tendency towards a likeness to the predominant species of Ithomia of the 

 respective localities. If the dress now woru by the Leptalis* was given it at its creation, 

 as Professor Westwood believed, how would he explain all these numerous shades of 

 variety found iu one and the same locality ? To be consistent he must say that each 

 variation was lineally descended from an originally created variety, which would be 

 absurd, as so many species are known to offer numerous similar varieties in one and the 

 same brood. As some of these varieties of Leptalis resembled species of Ithomia 

 peculiar to the locality more than their sister varieties did, the conclusion was simple 

 and natural, that, the imitation being a rule in all other localities, the process was there 

 at work by which the close imitation was brought about. The less exact imitations 

 were in course of time destroyed without bringing forth progeny, and then the state of 

 things was identical with what was found iu other localities, namely, one or more 

 constant forms of Leptalis resembling closely their companion Ithomia?. 



Dr. Sharp remarked that whether lire resemblances under discussion were purely 

 accidental or not could be determined by a numerical investigation, by ascertaining 

 what proporliou the cases in which species resembling one another occurred in 

 company bore to the cases in which species with a similar amount of resemblance 

 occurred away from one another. He thought, however, that some of the cases of 

 mimicry might be accounted for on other grounds than those supported by Messrs. 

 Wallace and Bates, for if the Darwinian theory of a common descent were true, then 

 the laws and principles of heredity could be applied to different species, as they have 

 heretefore been to individuals. He proposed four classes, uuder each of which he 

 believed some of these resemblances could be placed : — 



1st. Resemblances purely accidental ; for the doctrine of chances would show that 

 if there were in the world a sufficient number of species resembling one another, a 

 greater or less number of these would be sure to occur in company. 



2nd. Resemblances the result of a descent from a common parent; for it being 

 understood that a certain character would be transmitted from parent to offspring 

 through an indeGnite number of generations, unless circumstances tending to alter it 

 were brought to bear on that character, it could readily be perceived that some species 

 of Lepidoptera might resembie one another in coloration, by reason of the resemblance 

 of each to a common parent similarly coloured. 



3rd. Resemblances the result of exposure to similar circumstances ; for undoubtedly, 

 if the Darwinian theory were true, the coloration of species of Lepidoptera must be 

 referred sooner or later to external causes operating on the organism. But the 

 cases where mimicry occuiied were cases in which tue species, being constantly found 

 together, were necessarily to a very great extent subjected to the same external 

 cenditions. Tlius in a certain locality a species of Leptalis was found closely 

 resembling a species of Heliconia, and in another locality a second and allied species 

 of Heliconia was found. Mr. Wallace would say that this Heliconia differed from the 

 first Heiicouia because of the changed circumstances to which it was exposed: but 

 with this second species of Heliconia was found a second species of Leptalis, differiug 



