I893-] 



THE BRITISH NATURALIST. 



63 



exist at all. In the Highlands of Scotland, although the air be purity 

 and the sunshine brightness, the long, cold, wet winter, and the late 

 spring, can hardly fail to check the multiplication of those forms of 

 life which have their metropolis in warmer southern lands." Mr. 

 Birchall then goes on to show, by quotations from Darwin and Wallace 

 that black and dark colours are advantageous to animals, and con- 

 cludes his arguments thus : " As it appears certain that greater 

 strength of constitution and more powerful and acute perceptive 

 faculties are, from some yet unknown cause, associated with dark 

 colours. in the vertebrata, may we not presume that insects are subject 

 to the same law, and that dark varieties of Lepidoptera are able to 

 spread and increase under adverse conditions, whilst the lighter 

 coloured types fail to do so and are consequently eliminated in the 

 struggle for life, and that the occurrence of melanic forms may be 

 thus reasonably explained as a simple case of the survival of the 

 fittest." He then enumerated between 30 or 40 species of Lepidoptera 

 in which Melanism had been observed, a list which could now be 

 very largely added to. 



A long and interesting discussion ensued, both in the " Entomolo- 

 gist's Monthly Magazine" and in the "Entomologist," in which many 

 of the points only briefly touched on by Mr. Birchall were enlarged 

 upon and discussed at length. The only one of the various papers 

 which then appeared from which I need trouble you with quotations 

 is by Mr. Barrett "On the Degree of Tendency to Variation exhibited 

 by the Lepidoptera of Pembroke and Neighbourhood." He referred 

 first to the fact that " Lepidoptera whose larvae feed in trees are 

 almost totally absent." This he thinks arises from the mildness of 

 the winters and in a far larger degree from their extreme humidity, 

 but he thinks the principal cause of the exclusion of tree-feeding 

 species is " the furious violence of the storms, which, coming across 

 the Atlantic, rush upon this coast from the south-west with a fury 

 which the trees themselves can barely resist." He then comments 

 on the little variation he has observed, and concludes " that the 

 special peculiarity of climate likely to affect these species is its 

 excessive moisture, and that the tendency is (as suggested) to deepen 

 or intensify the colour and markings, but that there is not, with this 

 abundance of rain, an excessive decrease of light, since the rain tails 

 rapidly and heavily; there are comparatively few cloudy days without 

 rain in proportion to what are experienced in drier districts ; and the 

 frequent and brilliant sunshine and exquisitely clear and pure blue 

 sky affords a striking contrast to that of the Metropolitan and manu- 

 facturing districts in which cases of Melanism are so frequent, and 

 consequently cases of pure Melanism appear to be very rare here." 



In 1885, Lord Walsingham took for the subject of his Presidential 



