i893-] 



THE BRITISH NATURALIST. 



i53 



THE " MELANISM 



CONTROVERSY. 



BY W. E. SHARP. 



It is with considerable diffidence that I venture to add to the 

 embarrassing wealth of opinion, which this problem of the cause of 

 melanism among insects has evoked. Having, however, read most of 

 the literature of the subject, including Mr. Tutt's monograph 1 , Mr. 

 Robson's criticism 2 of that work, and lastly Mr. Tutt's rejoinder 3 ; it 

 has occurred to me, that the view this question assumes to one who 

 compensates for the disadvantage of not being a specialist in 

 Lepidoptera, by the advantage of having neither preconceptions to 

 sustain, nor theories to enunciate on the subject, might not be quite 

 devoid of interest. 



This problem, that of the origin of Melanism (and in this article I 

 use the word as expressing what is meant both by Melanism and 

 Melanochroism), is undoubtedly one of the greatest interest. It 

 submits to our consideration a series of the phenomena of vitality, 

 definite in character, and capable of investigation ; whose true solution 

 would vastly extend the limitations of our knowledge of the obscure 

 processes involved in that differentiation of form which we call the 

 origin of species. 



As such then it merits the attention of all biologists. 



Now, in any scientific enquiry, perhaps the highest essential is an 

 extreme accuracy and lucidity of thought ; and in all scientific contro- 

 versy more especially, that perfect adjustment of thought to expression, 

 which leaves the reader in no doubt as to the exact meaning of the 

 Writer. 



These fundamental requisites appear to me to have been consider- 

 ably neglected by most of the writers on this subject of melanism, 

 and the defect seems nowhere so apparent as in the writings of 

 Mr. Tutt. 



Let me then point out what I hold to be an initial confusion of 

 thought, by briefly defining the problem to be attacked. It is two-fold. 



(1) a. Certain species of Lepidoptera and Coleoptera 4 of general 

 distribution, exhibit in the British Islands, a tendency to melanism in 

 Northern districts, in Ireland and Man, and at high altitudes. 



1. "Melanism and Melanochroism in British Lepidoptera," by J. W. Tutt, f.e.s. 



Swan Sonnenschein & Co., 1891. 



2. See " British Naturalist," Vol. III., p.p. 61-64 and 65-71. 



3. See " Entomologist's Record," No. 5, Vol. IV. 



4. I omit, as far as possible, lists of specific names, as I apprehend that there is no 



material difference of opinion among Entomologists as to the species affected 

 by Melanism and Melanochroism. 



