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Show 1878.] HEMIPTERA OF ST. HELENA. 455 Cape of Good Hope towards the West Indies, and, while effectually stopping any emigration from the north, does, in fact, occasionally (as we shall presently see) bring new inhabitants to the island from the south. Given, therefore, any cause by which the present direction of the winds and currents could be reversed, the probability of colonization from the north would be immensely increased. But when we find, as in reality we do, that one and the same cause not only reversed the winds and currents, but induced an immense tide of migration to flow from the north to the south, then it seems pretty evident whence St. Helena derived its fauna, if that fauna be, as I shall presently show it is, of a Palaearctic character. The cause I have alluded to is one or other of the northern glacial periods, either the last or one in Miocene times. That during such a period the equatorial currents were reversed, Dr. Croll1 has shown there are very good reasons for believing; and as regards the flow of migration southwards at the same time, we know that that must necessarily have taken place2. But perhaps it may be argued that similar reasons to those which I have advanced to show that the colonization was from the north may be brought forward to prove, with as great probability, that the colonization was from the south. W e have seen, however, that the present configuration of the sea-bottom is much more in favour of the northern than of the southern theory; we, know, moreover, that emigration from the north has always been more powerful than from the south ; and I will try to show that the character of the fauna is in favour of the northern view. It is now generally admitted that the Cape-Verd Islands belong to the Palaearctic region, and have derived their fauna through the Canaries and Madeira. If, then, St. Helena got its fauna by that route from the north, the affinities should be Palaearctic, and the imprint of the fauna of the route should be more or less discernible. That this imprint is not more manifest is explained, I think, by reason that the route was interrupted at the St.-Helena end, and that island cut off, at a very remote date; the other islands being less inaccessible, have had their faunas altered very considerably by later importations, and their original settlers less modified by the fact that the colonization was more en masse and that fresh blood has tended to preserve the old types. Mr. Wollaston, whose opinion must be received with the greatest respect, arrived at the conclusion, as I have already mentioned, that St. Helena had little in common with the faunas of the Atlantic archipelagos to the north ; but even he admits that " two of the most significant of the Rhynchophorous types-namely Nesiotes (of the Tanyrhynchidce) and Acarodes (of the Anthribiidee)-are allied conspicuously to Echinosoma and Xenorchestes of the Madeiran archipelago." Most of the coleopterous genera not peculiar to St. Helena have already been cited in evidence of the very ancient peopling of the 1 Quoted in Dr. J. Geikie's ' Great Ice Age,' p. 107, &c. a Darwin, I. c. p. 339, &c. |