3IEL\N0CHR0ISM IN BRITISH LEl'IDOl'TERA. 1G7 



of these i-esting places is, to favour the most protected specimens, and 

 ^--liminate the least protected specimens, which I take it is "' natural 

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

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

 been inferentially explained or jiroven." 



Mr. Grote says : — " Melanism occurs sporadically Avith certain species, 

 and this also, in localities not particularly wet, and not at all smoky." 

 This is so, and is undoubtedly due generally to reversion, as I have 

 pointed out more than than once in Melanism and Melanochroisin, but with 

 regard to the preceding paragraph tliat " melanic parents do not produce 

 necessarily melanic progeny, or at least exclusively melanic races," it 

 must be admitted that the direct hereditary influence of the actual parents 

 is not sufficientl}^ powerful to do the latter completely, but in a large 

 degree, it is sufficiently powerful to produce a large percentage of melanic 

 specimens. We select black Amphidasys hetularia and black Tephrosia 

 crepmcidaria for the purpose of breeding black specimens, thus showing, 

 that whilst the general principle of hereditary tendency man gi'^"*^ ^^'^ 

 black specimens, the direct result arising from the selection of actually 

 black parents is enormously increased, and more certainly brings about 

 tlie desired result. We, in fact, change the probability of getting a 

 chance specimen or two of the desired dark colour, to the certainty of 

 getting a number of such. I am rpiite contra to Mr. Grote when he says 

 that " it does not seem to be jiroven that a greater total amount of dark 

 forms are absolutely ^^I'oduced in wet and smoky places." Practical 

 experience in Britain (at least) shows that such a statement is very 

 Avide of the mark, and there is no shadow of doubt that there is a 

 much larger total number of dark forms produced in wet and smoky 

 places, for only in such places do we get dark specimens of many 

 species at all. The second part of this paragi-aph, in Avhich Mr. Grote 

 says " the pale forms would be the first to be destroyed " owing '• to 

 the consequent attention of their natural enemies," and that, therefore, 

 as a result, " the dark forms would appear to be more plentifully pro- 

 duced, because artificially preserved," will not hold water, because 

 such an excess is equally observable in bred specimens from such 

 localities and is not a resultant of anything taking place after the moths 

 have emerged. In fact, were the suggestion which Mr. Grote makes, 

 possible, it would result that " melanism " is now in existence on a 

 large scale everywhere, and that the general result was due to nothing 

 but " natural selection " of the most pronounced kind on each indi- 

 vidual brood. But that is not so. We breed pale races from certain 

 localities ; we breed dark races from other localities, with an occasional 

 •odd variety either way : but every brood is not a mixture of dark and 

 light specimens, of Avhich the former are destroyed every year in one 

 locality, and the latter in another. I quite agree with Mr. Grote in 

 his general notion that many species were originally dark ; I stated so 

 expressly in my paper, and have repeated the statement more than once 

 since. I also agree that in many instances the present melanic races 

 are outcomes of hereditary tendency or reversion towards this original 

 form, and that there is, therefore, an inlierent tendency in the insect 

 to become dark. What we are concerned with, is not so much the in- 

 herent capacity in insects to vary, which we all acknowledge to exist, 

 but with the forces in existence at the present time, which will draw 

 out these latent tendencies, and which cause the insect to make these 



