^V' AND ^^^^ 



JOURNAL OF VARIATION. 



No. 5. Vol IV. May 15th, 1893. 



]VIEL^rlOepll^OI^]VI I]\[ BI^II'I^JI LEPIDOPfEI^^.* 



An Answer to Mr. Eobson's Criticisji, "Is Moisture the Cause 



OF Melanism? " 



By J. W. TUTT, F.E.S. 



It is difficult to deal with Mr, Eobson's paper, " Is Moisture the 

 Cause of Melanism ? " read before the City of London Ent. Society on 

 Feb. 21st last, without going into considerable detail, without going- 

 over ground already repeatedly trodden, and finally, without taking 

 too serious notice of a paper which contains no single item on the 

 subject which has not been thoroughly discussed before. 



Some little time ago it will be in your recollection, I published a 

 pamphlet on Melanism and Melanochroism in British Lepidoptera, in 

 which I summarised the various articles \vTitten by more or less compe- 

 tent students of lepidoptera, and criticised the various suggestions as to 

 its cause which had been offered. Mr. Eobson's pa^^er briefly passes in 

 review a few of these summarised papers, and then goes on to criticise 

 at length one view that I brought forward, viz., the connection between 

 moistvire and melanism. In my pamphlet I proved conclusively that 

 areas, which were excessively humid, and those that had by recent arti- 

 ficial change of environment, produced dark surfaces, &c. (such being 

 frequently increased by rain), also produced melanic races of certain 

 species, and these, I considered, essentially due to three things, (1) the 

 action of the moisture constitutionally on the larva ; (2) the darkening 

 of the surfaces by rain, smoke (or both combined), etc. ; (3) the general 

 action of "natural selection." 



To begin with, the title of Mr. Eobson's paper is essentially mis- 

 leading as a criticism. If he had written " Is moisture a cause of me- 

 lanism ? " we might have obtained some useful result, but " tlie cause " 

 obviously shuts out all other considerations, and at once levels the 

 paper to a reductio ad absurdum. 



I will now consider a few of the points touched upon. Mr, Eobson 

 begins by the effusive praise of a paper of Mr. Birchall which was 

 wi-itten in 1876, and which made some comprehensive generalisations 

 without working out or even suggesting any reason which could be 

 acted on by scientific men. Dr. White seems to have been the only 



* Paper read befoi'e the City of London Entomological Society, May 2nd, 1893. 



