MELANISM AND MELANOCHROISM IN BRITISH 

 LEPIDOPTERA. 



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



"Melanism" in Lepidoptera is a subject which has now 

 """ and again been brought before the entomological public, 

 and discussions as to its origin and distribution have occa- 

 sionally taken place in the British entomological journals. In 

 these discussions, the subject was generally treated from 

 an insular point of view, until Mr. Dobree {Entom. xx., 

 pp. 25-28) endeavoured, by comparing our melanic forms 

 with the forms of the same species obtained on the Con- 

 tinent, to correlate the facts obtained, and to show the real 

 relation that not only our melanic, but also our ordinary 

 forms bore to the Palsearctic lepidopterous fauna, and to 

 deduce reasons for the melanism so prevalent in our British 

 forms. In dealing with melanism it is advisable in the first 

 place to bear in mind what we include in that term. Melan- 

 ism, properly speaking, refers only to an increase in the 

 quantity of actually black markings at the expense of any 

 other colour. It has not been customary, however, to base 

 or confine our arguments to this restricted view of the subject, 

 but any darkening of the ground colour, whether black or not, 

 has been included in a general way in the term. However, as 

 this was not strictly correct. Dr. F. Buchanan White {E?ii. 

 Mo. Mag., vol. xiii., p. 145) suggested for this general 

 darkening of the ground colour the term " melanochroism," 

 whilst the opposite phase of variation, the development of a 

 paler pigment at the expense of a darker, he called " leuco- 

 chroism." Thus, Ainphidasys betularia var. dcubledayaria, is 

 a case of true " melanism." The development of buff and 

 yellow coloration, instead of white, in Arctia mcntJiastri is a 

 case of " melanochroism." It will be seen that most of the 

 cases referred to in the discussions on "melanism" are really 

 not true melanic forms, but really melanochroic forms, because 

 the species are but rarely suffused actually with black, although 

 there may be a great deepening in the ground colour, the 

 depth of the colour being, however, frequently increased by a 

 colour other than black. A good example of " leucochroism " 

 is that of Arctia plantaginis var. hospita. In this variety the 

 orange of both the anterior and posterior wings is replaced 

 by white. 



I believe Mr. Cockerell was the first entomologist who 



