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Show 1897.] FROM SOUTH AFRICA. 345 setae is quite smooth; but a little way in front of this the shaft of the seta is encircled by a series of ridges which are perfectly smooth and not denticulate in any way; their direction is curved. § General Remarks. This interesting collection of Acanthodrilus suggests several observations of a general character. In the first place, to meet with the genus so very prevalently in the Cape Colony is remarkable, though not perhaps altogether unexpected. That there are so many species (10) seems to negative any suggestion of accidental importation, as does their occurrence not only in the near neighbourhood of Cape Town, but at such distant places as the Knysna Forest. There is also the noteworthy fact that the Acanthodrlli of South Africa belong to a distinct group of the genus, not unknown it is true elsewhere, as will be pointed out presently, but embracing all the species (with the possible exception of the originally described species Acanthodrilus capensis). This again is not suggestive of accidental importation. It may, I think, be fairly assumed that the species described in the present communication are truly indigenous. This being the case, we have a fauna of Earthworms in the temperate part of the African continent which is totally unlike that of tropical regions (characterized as it is by the Eudrilidae and by the Acanthodrilid Benhamia, not Acanthodrilus) of that continent, and like that of South America and N e w Zealand. W e have, in fact, in the three great land-masses which extend from the northern into the southern hemisphere-if we may allow a former connection between Australia and N e w Zealand-a sharp demarcation between the earthworm fauna of their southern and of their equatorial regions. In all of them Acanthodrilus is the prevalent genus of the Antarctic half. The bearing of this fact upon the theory of a former extension northward of the existing Anctartic continent has been so often referred to by me, that I need do no more than allude to it. I may, however, remark that since I have written upon that matter Dr. Eisen has described two species of Acanthodrilus from California. But I a m of opinion that this fact, like the spreading northward of Mlcroscolex, is not fatal to m y views. To assume the converse, that this genus has started in the north and migrated southwards, is difficult1 if w e keep firmly hold of the fact that there is so little difference between the species of Patagonia and the Cape of Good Hope, not to mention New- Zealand. The only alternative is to assume what is certainly becoming more and more fashionable as an assumption-a twofold or three-fold origin of the worms which are here, and by all other writers, placed in one genus, Acanthodrilus. If, however, this view is to be entertained at all it cannot, in m y opinion, be 1 Since these words were written I have received from Dr. Michaelsen a paper (" Weiterer Beitrag zur Systematik der Regenwiirmer," Verh. Hamburg, 1896) in which the tropical origin of Acanthodrilus is ably urged. PROC. ZOOL. Soc-1897, No. XXIII. 23 |