MELANOCHROISM IN BRITISH LEPIDOPTERA. 197 



which damp can affect the larvae so as to produce melanic moths. But 

 if, as Mr. Tutt says, by artificially selecting black parents the direct 

 result is that in their progeny the number of black individuals is enor- 

 mously increased, then it is clear that such selection, either natural or 

 artificial, may be one of the forces leading to the display of the latent 

 tendency to melanism existing in certain species as a character of 

 reversion. As a matter of fact, I was ignorant that this was experi- 

 mentally i^roven. We have now, then, the two facts to go upon, that 

 damp and smoky places produce a greater total amount of melanic 

 individuals, and that by breeding from melanic parents, the number of 

 black specimens in the progeny much exceeds the number found in 

 broods of the type form. The question still remains as to why wet and 

 smoke produce melanism. The answer is suggested by Mr. Tutt that 

 damp and smoke (or darkness) artificially produce to-day a resemblance 

 in conditions to the environment of the species in geological epochs 

 when its tyj^ical form was black. Now remains the query as to 

 whether any of our exceptional localities of to-day are sufficiently damp 

 and dark as to be j^roiDerly comj^ared with general conditions in any 

 former geological epoch in which dampness and darkness were the 

 general rule, affecting geological life generally ? As to hoio wet pro- 

 duces melanism I do not understand the question to be at all answered. 

 But in what way does a renewal of a physical environment, which was 

 once normal to the species, act upon its now normal colouring so as to 

 produce reversion to a former colouring? The experiments with 

 Indian butterflies go to show, that there may be a connection between 

 dry or wet conditions and dimorphism, and I think, do not entirely 

 cover the present question. They seem to run parallel with Edwards' 

 experiments with American dimorphic or polymorphic butterflies, and 

 show that, by an imitation of seasonal conditions, alteration of tempera- 

 ture and humidity, a tendency to meet these conditions is shown in the 

 colours and pattern of the insects. Is dimorphism parallel with 

 melanism, are both phenomena of reversion ? Is the wet dimorphic 

 form the older, reversional form of the species ? Does the wet tropical 

 season answer to the normal physical conditions in a former geological 

 epoch ? To my suggestion that dark resting places are protective to 

 dark forms, Mr. Tutt says, that " the direct result of the protective 

 nature of these resting places is, to favour the most protected specimens 

 and eliminate the least protected specimens, which I take it is " natural 

 selection," and which, therefore, renders abortive Mr. Grote's previous 

 suggestion ' that the modus operandi of natural selection has only been 

 inferentially explained or proven ' (i..e., in the present case)." Now, in my 

 argument as to the protection afforded by dark resting places, T distin- 

 guished between an apparent artificial survival throvigh protective causes 

 and a real survival of the fittest, under the law of " natural selection." 

 If dark resting places however really produce a larger total number of 

 dark specimens, then, in such places, instances where both parents are 

 dark, would be naturally more numerous, and if (as Mr. Tutt says is 

 proven) the production of melanic progeny is directly influenced by the 

 colour of the parents, then, the presence of melanic breeds in certain 

 localities would be sufficiently accounted for. Still, in all this, we have 

 to deal with a character of transmission or reversion, and the utmost we 

 seem to have proved is, that melanism usually exhibited at the longer 

 interval of reversion, is to some extent exhibited also at the shorter 



