The _Mesites Maderensis_, Woll., to which I alluded in the above quotation, is undoubtedly a strong case in point. Although specifically dissimilar from the _M. Tardii_, its Irish counterpart, it nevertheless approaches it so closely, that it might be literally mistaken, _prima facie_, for that insect; and we know that it is one of the plans on which Nature commonly proceeds, that species which are not merely representative of (or analogous to) each other, but which are actual homologues, or allies, should usually emanate at first from foci not far removed _inter se_; or, at all events, if distant, connected by an intervening land:--in other words, that _generic areas_, no less than specific centres, of radiation, form a substantial item of the comprehensive scheme on which the system of created things was originally planned. We detect traces of this primary law in each division, or class, of the organic world; nor is its reality _as a law_ interfered with, through the occasional exceptions which are liable, as in every other instance, to present themselves. Such deviations are often easily to be accounted for, whether by natural or artificial means; and do not affect the subject, as a whole. Sometimes indeed they become at once intelligible from the historical records connected with them, proving that human agencies have been at work acting as transporting media, within a period comparatively recent; whilst at others, the fact of the creature having been endowed with self-diffusive powers to an extravagant degree may succeed equally in rendering the phaenomena explicable. But, even where neither of these solutions would seem to suffice, we should still recollect that it is only in the mass that such questions can be pronounced upon; and that, consequently, where we are able to discover a rule which is _for the most part_ adhered to, it is more philosophical to conclude that the departures from it are the result of special disturbing causes (whatsoever they may have been), than to permit them to undermine our faith in what would be otherwise universally true. Thus, the botanist tells us of Ixias, Stapelias, Mesembrianthemums, Pelargoniums, and Euphorbias, as concentrated in Southern Africa; of Magnolias in Central America; of Calceolarias on the Andes; of Myrtles, Banksias, Mimosas, and _Eucalypti_, in Australia; and of the Bread-fruit Trees in the South Sea Islands: the ornithologist points, _inter alia_, to the Toucans and Humming-Birds from South America and the West Indies; whilst the student of the higher animals informs us of the Kangaroos (indeed of the whole of the subclass _Marsupialia_, except the genus _Didelphys_) as peculiar to Australia and a few islands to the north of it; of _Lemur_ _proper_ to Madagascar; of the Sloths, Armadillos, Tree Porcupines, and of Alligators, and of the _Platyrrhini_ (amongst the Monkeys), to South America; and of the Ourangs to the islands of the Indian Archipelago.