I have before announced my conviction, that _generic areas_ have a real existence in Nature's scheme; and that, consequently, where species which are so intimately allied that they can with difficulty be distinguished, prevail, there is presumptive reason to suspect (until at least the contrary is rendered probable) that the areas which they now colonize were once connected by an intervening land,--or, in other words, that the migrations of the latter were brought about, through ordinary diffusive powers, from specific centres within a moderate distance of each other. I say "_presumptive_ reason," because there are undoubted exceptions to this law (as to every other), and it can therefore be only judged of on a broad scale. Still, I contend that in a wide sense it holds good; and that, consequently, if closely related "species" are traceable in countries which geology demonstrates to have been far asunder during the _entire_ interval since the first appearance of the present animals and plants upon our earth, there is at any rate an _a priori_ probability that they are no _species_ at all,--but permanent geographical states, which have been slowly matured since their casual introduction beyond their legitimate bounds. If we except those forms which are in reality but modifications, from climatal and other causes (and which have, therefore, been wrongly quoted as distinct); I believe that a vast proportion of the species which have been usually considered to be "representative" ones, were members, in the first instance, of the self-same assemblages,--which had wandered to a distance from their primaeval haunts, and were afterwards, through the submergence of the intervening land, cut off from their allies. I have adduced, in a preceding chapter, some remarkable examples in illustration of this hypothesis,--an hypothesis which I believe to be the true clue to a very large item of the "specific representation" theory. A considerable number of the Madeiran _Helices_ may be cited (which I have already done[85]) as, in the strictest sense, representative of each other,--and as therefore specifically distinct: and I may add, that it is to island groups that we must mainly look for this system in its full development. But, apart from the fact that I would not wish to resign _in toto_ the doctrine of "specific representation," even as frequently understood (that is to say, as recognizable in countries which have been altogether disconnected since the last creative epoch), and therefore, _a fortiori_, in what I conceive to be its truer meaning; there is yet another point on which I would desire to be interpreted aright, whilst endeavouring to substantiate the action of local influences on the members of the insect world. It has been my aim, in the preceding pages, to call attention to the importance of external circumstances and conditions in regulating, within definite limits, the outward aspect of the Articulate tribes.