MELANISM AND MELANOCHROISM. 58 



Islands are more humid than the eastern, and the Gulf Stream 

 exerts its greatest influence on the western shores of Ireland, 

 the north-western shores of England and Scotland and the 

 Northern Islands; and here, following out the connection of 

 humidity and melanism, we find that, in those districts, the 

 humidity ^ of which is so striking, we get our most pronounced 

 forms of melanism. The blackness and intensity of ccjlour 

 of certain forms of lepidoptera, especially among the Noctu.-e 

 from Sligo, Rannoch, the Hebrides, Orkneys and Shetlands 

 are most striking and remarkable, and here are our most 

 humid districts. In a lesser degree the lepidoptera of Eastern 

 and Southern Scotland and North and North-western England 

 show general melanism, but rather less intensity of develop- 

 ment in some particular species. Then comes the melanism 

 of Wales and the Midlands ; and lastly, the ordinary melanism 

 found in the species of our south and south-eastern districts as 

 compared with the forms of the same species obtained on the 

 Continent. In other w^ords, we find a certain gradation, 

 corresponding, in a general way, with the gradation in 

 humidity. 



With regard to the insects on our south and south-eastern 

 coasts, it is rather remarkable that the difference between them 

 and those of the corresponding coasts of the Continent should 

 be so very marked ; but it is so, and I am not surprised that 

 Mr. Dobree {Entom. xx., p. 28) should have come to the con- 

 clusion that "the inference can be drawn that the melanism is 

 primarily due to the particular geographical position of these 

 islands." To complete the connection between the relation 

 which I have tried to prove exists between " humidity " and 

 " melanism," it would be interesting to know whether the 

 influence of the Gulf Stream makes itself felt sufficiently to 

 produce melanic forms on the western coast of the Scan- 

 dinavian Peninsula, I know nothing of the fauna of this 

 district ; but if melanism occurs there, it would do much to 

 strengthen the view taken. 



That this melanism exists in Scandinavia the following note 

 from Professor Schoyen, Christiania, will show : — " The 

 tendency to melanism in our lepidoptera is certainly, as a rule, 

 more apparent on the western shores than in the eastern 

 districts of the country, even at a less height above the sea- 

 level ; in some cases this is as marked as in the mountainous 

 tracts, — e.g. Cidaria flavicinctata occurs at the town Molde in 



^ i.c. "Humidity" apart from heavy rainfall. 



