December, 1870.] 1.4<5 



ON MELANOCnROISM AND LEUCOCHROISM. 

 BY P. BUCHANAN WHITE, M.D., P.L.S. 



Climatic variation is a subject that has always possessed great 

 attractions for me ; it was, therefore, with much interest that I read 

 my friend Mr. Birchall's notes " On Melanism," at p. 130. 



Mr. Birchall begins by stating " that sj^ccimens of many 

 Lepidoptera, from the Highlands of Scotland, vary widely from 

 English examples of the same species, and that the variation is usually 

 towards a darker coloration ; that there is, in short, a tendency to the 

 production of melauic varieties, and that in some cases a dark variety 

 has completely supplanted the lighter coloured type." 



That there is frequently a difference between South English and 

 Highland examples of the same species will be admitted I think by 

 every one ; and that this variation is, in the majority of cases, in the 

 direction of melanism, has been generally taken for granted. That it 

 really is so, the following brief analysis of the Highland Lepidoptera 

 will show. In it I have compared the majority of the Macro-Lepi- 

 doptera of Scotland north of the Tay with South English (and in a 

 few cases with South European) specimens of the same species ; for 

 it must be remembered that North or North- West English specimens 

 frequently exhibit the same, or even a greater, tendency to melanism, 

 than the Highland specimens. 



Before beginning the analysis it may be as well to define what is 

 meant by "melanism." 



Strictly speaking the term "melanism" ought to be restricted to 

 such forms as Amplddasis hetularia ab-. Douhledayaria, Mill., which 

 are more or less inf uscated with hlack ; but, as in that variety, the 

 melanism is due to the excessive increase of the markings at the 

 expense of the ground colour, therefore all cases wherein there is 

 a tendency to a suffusion with darker colour,^ or where the markings 

 and ground colour are alike deepened, must be considered as melanic, 

 as well as those cases where the melanism is produced by suffusion 

 with black. To take an extreme case, a change from a white to an 

 ochreous ground colour, must be regarded as melapism. "Melanism" 

 is not I think a good term for all these various cases, and I would 

 suggest the use of the term " melanochroism " as preferable. On the 

 other hand, " leucochroism " is the very opposite to "mehinochroism." 

 By leucochroism I do not mean " albinoism," which ought to be 

 regarded as a more or less diseased or abnormal condition. Any 

 change to a paler c(dour (as from ochreous to white), or where 



