106 DARAVmiSM chap. 



to whom wings were not absolutely essential escaped a serious 

 danger by not using them, and the wings therefore became 

 reduced or were completely lost. But when they were essential 

 they were enlarged and strengthened, so that the insect could 

 battle against the winds and save itself from destruction at 

 sea. j\Iany flying insects, not A'arying fast enough, would be 

 destroyed before they could establish themselves, and thus we 

 may explain the total absence from Madeira of several whole 

 families of winged insects which must have had many oppor- 

 tunities of reaching the islands. Such are the large groups of 

 the tiger-beetles (Cicindelidie), the chafers (Melolonthidie), the 

 click-beetles (Elateridte), and many others. 



But the most curious and strikina; confirmation of this 

 portion of Mr. Darwin's theory is afforded by the case of 

 Kerguelen Island. This island was visited by the Transit of 

 Venus expedition. It is one of the stormiest places on the 

 globe, being subject to almost perjDetual gales, while, there 

 being no wood, it is almost entirely without shelter. The 

 Rev. A. E. Eaton, an experienced entomologist, Avas naturalist 

 to the expedition, and he assiduously collected the few insects 

 that were to be found. All were incapable of flight, and most 

 of them entirely ■without Avings. They included a moth, 

 several flies, and numerous beetles. As these insects could 

 hardly have reached the islands in a wingless state, even if 

 there were any other known land inhabited by them — which 

 there is not — we must assume that, like the Madeiran insects, 

 they Avere originally Avinged, and lost their poAver of flight 

 because its possession Avas injurious to them. 



It is no doubt due to the same cause that some butterflies 

 on small and exposed islands have their Avings reduced in size, 

 as is strikingly the case Avith the small tortoise-shell butterfly 

 (Vanessa urticie) inhabiting the Isle of Man, Avhich is only 

 about half the size of the same species in England or Ireland ; 

 and Mr. Wollaston notes that Vanessa callirhoe — a closely allied 

 South European form of our red-admiral butterfly — is perma- 

 nently smaller in the small and bare island of Porto Santo 

 than in the larger and more Avooded adjacent island of Madeira. 



A very good example of comparatively recent divergence 

 of character, in accordance Avith neAv conditions of life, is 

 afforded by our red grouse. This bird, the Lagopus scoticus of 



