XII THE COLEOPTERA OF MADEIRA 255 



and thus their wings became more and more developed in 

 each succeeding generation. 



Now this view of the case enables us at once to explain 

 some of the most striking gaps in the Madeiran coleop- 

 terous fauna. The Cicindelidse, for instance, are entirely 

 absent ; and almost all the European species are winged 

 insects of somewhat feeble flight, yet to whom flight is 

 necessary. We can readily understand that such insects 

 would be easily exterminated if they arrived singly or in 

 small numbers ; though it is not so easy to understand 

 why, in a forest-clad island, some of the sylvan species 

 should not have found a home had the land ever been con- 

 nected with a continent where they abound. Their total 

 absence is, therefore, decidedly unfavourable to the theory 

 of a land-connection with Europe. To the Melolonthidse 

 and Cetoniidoe,. as Avell as the Eumolpidse and Galerucidse, 

 which are all wanting, the same argument will apply ; and 

 also to the Elateridse and Buprestidse, which are repre- 

 sented each by one minute species. But if Madeira is the 

 remains of a continent once continuous with the south of 

 Europe and deriving its fauna from such continuity, how 

 are we to explain the absence of extensive genera very 

 abundant in South Europe, and, from their being apterous, 

 specially adapted to the peculiarities of Madeira ? Such 

 are Carabus, Lampyris, Pimelia, Akis, and many others. 

 But these facts are all consistent with the theory of intro- 

 duction across the sea. Apterous groups, however abun- 

 dant on the continent, should, as a rule, be absent ; and I 

 find that almost all the European apterous genera are 

 wanting, and among the few exceptions there are some 

 whose presence is easily explained and really prove the 

 rule. We must remember, however, that the apterous 

 condition, except in those cases where it is characteristic 

 of an extensive group, is one of little stability or import- 

 tance. There are species which are sometimes apterous 

 and sometimes winged, and we may therefore be sure, 

 that if any advantage was to be derived by either con- 

 dition over the other, natural selection would very rapidly 

 render it constant by the repeated survival of the favoured 

 individuals. This is illustrated by the fact that we have 



