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 direc- 

 tion 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. Croll 1 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 place 2 . 



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. We 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 Palsearctic 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 consider- 

 ably 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 

 Tanyrhynchidcp.) and Acarodes (of the Anthribiidce) — are allied con- 

 spicuously to Echinosoma and Xenorchestes of the Madeiran archi- 

 pelago." 



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. 



