The geographical distribution of animals, with a study of the relations ...

chap, x.] THE PAL^ARCTIC REGION. 213islands and also occurs in South Europe, but isalways apterous.It is however closely allied to another genus, Cryptorhynchus,which is apterous in some species, winged in others. We maytherefore well suppose that the ancestors of A calks were once inthe same condition, and that some of the winged forms reachedMadeira, the genus having since become wholly apterous.We may look at this curious subject in another way. TheColeoptera of Madeira may be divided into those which arefound also in Europe or the other islands, and those which arepeculiar to it. On the theory of introduction by accidentalimmigration across the sea, the latter must be the more ancient,since they have had time to become modified ;while the formerare comparatively recent, and their introduction may be supposedto be now going on. The peculiar influence of Madeira inaborting the wings should, therefore, have actedon the ancientand changed forms much more powerfully than on the recentand unchanged forms. On carefully comparing the two sets ofinsects (omitting those which have almost certainly beenintroduced by man) we find, that out of 263 species whichhave a wide range, only 14 are apterous ;while the other class,consisting of 393 species, has no less than 178 apterous ; orabout 5 per cent in the one case, and 45 per cent in the other. 1On the theory of a land connection as the main agent in introducingthe fauna, both groups must have been introduced at orabout the same time, and why one set should have lost theirwings and the other not, isquite inexplicable.TakiDg all these singular facts, in connection with the totalabsence of all truly indigenous terrestrial mammalia and reptilesfrom these islands—even from the extensive group of the Canariesso comparatively near to the continent, we are forced toreject the theory of a land connection as quite untenable ;andthis view becomes almost demonstrated by the case of theAzores, which being so much further off, and surrounded bysuch avast expanse of deep ocean, could only have been con-1The facts on which these statements rest, will be found more fullydetailed in the Author's Presidential Address to the Entomological Societyof London for the year 1871.