1(36 THE entomologist's record. 



natural enemies. The dai'k forms woi;ld appear to be more plentifully 

 produced because ai-tificially preserved from their resemblance to their 

 environment and the consequent inattention of their natural enemies. 

 We cannot call " natural selection " to solve the problem, unless we 

 regard melanism as a step, however small or large, however uncertain, 

 in the direction of specific separation. So far as my studies on 

 American Lepidoptera go, I have shown the probability that in such 

 genera as Basilarchia (Lhnimtis, part. Auct.), Datana, Plahjsamia, 

 Hemileuca, the separation of species has been comparatively recent, but 

 in whatever way the separation has been effected, it has clearly not 

 been due to the appearance of characters at reversion or inheritance, 

 but to some new " force " impelling a change in a fresh direction, to a 

 splitting of an original type into "varieties," "races," and finally, 

 " species," Avhich may, in some cases, occupy the same territory, and be 

 subject to the same climatic conditions. Going hand in hand with 

 this " force," which has caused the splitting up of what was once 

 probably a single "species" into what is now half a dozen, there has 

 been an inherent adaptability displayed by the original species, a want 

 of resistance to whatever has caused the splitting of the original type. 

 Thus some types are shown to be more plastic than others, to be less 

 original and firmly moulded. Such insects as Pygcera buccphala and 

 Datana ministra (not improbably identical in the Tertiary epochs) are 

 examples of these plastic forms. The characters displayed under 

 variation need a categorical separation as to their significance and 

 value. — Bremen, Germany. May, 1893. 



I do not quite follow Mr. Grote's reasoning when he says, " I think 

 we may eliminate from the problem the action of ' natural selection ' 

 and the effect of humidity on the larvfe, because these are factors, the 

 vwdus operandi of which has not been, in the latter case, scientifically, 

 in the former, here only inferentially, explained or proven." The 

 action of humidity in producing ordinary variation has been, in a 

 degree, scientifically proved since exi^eriments on seasonally dimorphic 

 Indian butterflies have been carefully carried out, and it has been 

 shown that by artificially exposing larva3 of the different broods to the 

 opposite conditions to those to which they would naturally be exposed, 

 the resultant imagines were of the type generated by the surroundings, 

 in spite of what we may assume to have been the hereditary tendency 

 in the opposite direction ; so that exposure to a moist or a dry 

 atmosphere, resulted in the production of the " dry " and " wet " season 

 forms. Hence it seems that there is a direct connection and a direct 

 action on the larva. With regard to the influence of " natural selection " 

 having been " only inferentially explained or proven," it can only be 

 admitted that such is the case to the extent that all references to 

 " natural selection " are necessarily in the way of inference, rather 

 than of actual fact, the inferences, however, being based on observed 

 facts. In the case of observation in this direction, however, on many 

 lepidoptera, the inferences are so palpable as to be almost as patent as 

 the facts, and these can scarcely be eliminated in any explanation given. 

 Mr. Grote further says : — " May not the explanation be that the 

 dark resting places are protective ? " I think I have fully proved that 

 the resting places are protective, and it is on the undoubted fact under- 

 lying Mr. Grote's present query, that the influence of " natural selec- 

 tion " has its strong basis, for the direct result of the protective nature 



