CH. IV] LEPIDOPTERA OF ISLE OF MAN. 217 



the fact that in the Galapagos and Kerguelen many of 

 the insects are flightless. The same is the case with 

 other oceanic islands. But in other cases the insects 

 have larger wings than their allies upon the mainland. 

 These two facts are both explained in the same way by 

 Mr Darwin. The small size of the islands and the frequent 

 prevalence of gales of wind would tend to blow the insects 

 out to sea, where they would in all probability perish. 

 Those individuals therefore which either had wings un- 

 commonly strong or were incapable of flight altogether 

 would have the best chance of maintaining their footing. 

 The same need has thus produced two effects of the most 

 opposite kind. 



Prof. Eimer has remarked upon the fact that "the 

 butterflies of Sardinia are in general smaller and also 

 more darkly coloured than those of the mainland." The 

 same thing exactly is met with in the case of the variety 

 of the small Tortoiseshell butterfly upon the Isle of Man. 

 This island has other insects which are darker in colour 

 than those upon the neighbouring mainland. Diantlicecm 

 capsophila is a variety of the more usual D. carpoplwga ; 

 in Ireland the examples of this variety are dark coloured, 

 but those of the Isle of Man are more darkly coloured 

 still. Mr Wallace mentions four other moths which show 

 some such difference from their representatives upon the 

 mainland. The somewhat rare Cirrhcedia xerampelina is 

 not much darker than the mainland form but it differs 

 from it in the production of a characteristic yellow line. 

 The late Mr J. Jenner Weir, a well-known entomologist, 

 noted that several of the Geometer moths of the Hebrides 



