July 13, 1905] 



NATURE 



H5 



It is very improbable that the ancestors of these minute 

 insects were carried or blown to where they are now found ; 

 they must have travelled to their present positions by land. 

 That is, the Antarctic continent south of New Zealand 

 and Patagonia must, at some time or other, have joined 

 on to northern lands. 



In the islands of the Antarctic Ocean we have further 

 evidence of a former land connection in the earthworms 

 belonging to the family Acanthodrilidae, which are 

 characteristic of Antarctic regions. A spider also lives on 

 Bounty Islands which is closely related to one from Cape 

 Horn. But spiders seem to have special facilities for 

 crossing barriers, and the insects found on Bounty Islands 

 are all related to New Zealand forms. I do not include 

 here the evidence of the plants of the Antarctic islands, 

 for most plants do not require that the land should be 

 actually continuous to enable them to spread. 



But if the flightless insects and the earthworms imply 

 a former connection with northern lands, that connection 

 must have been a very long time ago, before the spread 

 of insects and angiospermous plants over the world, that 

 is, not later than the Jurassic period. If there had been 

 any land connection in Tertiary times, there w'ould have 

 been a much greater mixing of the animals and plants. 



It is evident that the flora, and perhaps the fauna, of 

 Antarctica were formerly much richer than at present, as 

 is proved by the fossil plants of South Victoria Land, and 

 it is also probable that both fauna and flora were killed off 

 by an increasingly rigorous climate. It is not necessary 

 to assume a former Glacial epoch for this, for higher plants 

 and animals could hardly resist the present climate, and 

 there is no palaeontological evidence of a period of greater 

 cold than now having ever existed in the southern hemi- 

 sphere. On the contrary, the biological as well as the 

 palseontological evidence is against the idea. For the 

 much modified plover, Chionis, and the insects of 

 Kerguelen Land, as w-ell as the remarkable flora of the 

 .Antarctic islands, show that the islands could not have 

 been covered with ice for a very long time. 



The relations between the avifaunas of Australia and 

 South Africa are much closer than exist between those of 

 .Australia and South America, and this is just what we 

 should expect if the ancestors of the present birds had 

 spread down from the north under the present condition of 

 land and sea, for the land connection between Australia 

 and South Africa is far more intimate than that between 

 the former place and South America. But the contrary 

 is the case with the Mammalia, some of the tortoises, 

 snakes, frogs, some of the fresh-water fishes, a large 

 number of insects, and the family Cryptodrilidse of earth- 

 worms. This implies that at some former time a closer 

 connection existed between .Australia and South America 

 than between Australia and Africa. The question is. Was 

 this connection by means of an Antarctic continent? Or 

 was it by a Pacific continent? 



The principal objection to the southern route is that 

 the connection between Australia and South America is 

 shown by a number of subtropical animals — such as 

 Osteoglossum and Ceratodus — none of which have left any 

 trace of their passage through New Zealand. We cannot 

 suppose that New Zealand was disconnected at the time 

 from the Antarctic continent, for it, also, has distinct 

 relations with South America, but for the most part by 

 means of different animals from those which show the 

 Australian connection. If the connection was in either 

 the Cretaceous or the Eocene period, we might suppose 

 that the climate was warm enough for the passage of 

 the subtropical animals by the Antarctic route, but, if so, 

 why are there no traces of marsupials and South American 

 frogs in New Zealand? If, on the other hand, we sup- 

 pose the ancestors of these animals to have crossed from 

 .Australia to South America by a South Pacific continent, 

 we can understand how the subtropical forms would not 

 have come so far south as New Zealand, while the New 

 Zealand forms would have crossed at a higher latitude. 

 In favour of this we have a member of the Iguanidae in 

 Fiji, as well as the evidence of the land shells of Polynesia, 

 which are not a collection of waifs and strays, but form 

 a distinct group of a very early type, which, however, 

 has not yet been found in South America. 



NO. 1863, VOL. 72] 



We still have to consider the floras and the marine 

 faunas of the -Antarctic islands. Here we see a number 

 of birds — such as cormorants and gulls — as well as fishes 

 and plants, which could hardly spread round the world 

 under the present conditions of land and water. That 

 this spreading was a comparatively late one is proved by 

 the near relations between the species. But if there had 

 been continuous land at the time, land animals would have 

 spread with the marine ones. It is therefore necessary 

 to suppose that this last spreading of species in Antarctic 

 latitudes was by means of a number of islands. Probably 

 this was in Pliocene times, it we may judge by the amount 

 of differentiation which has taken place since then. 



I therefore conclude that the hypothesis which best 

 explains the phenomena is the following : — 



(i) That in the Jurassic period an Antarctic continent 

 existed which connected South America with New Zealand 

 and South Africa. 



(2) That this continent sank in the Cretaceous period, 

 and that Antarctica has never since been connected with 

 northern lands. 



(3) That in the Cretaceous or early Eocene a Pacific 

 continent connected New Guinea and New Zealand with 

 Chili. 



(4) That this land sank at the close of the Eocene. 



(5) That in the Pliocene a number of islands existed in 

 the Antarctic Ocean, which have since then disappeared. 



F. W. HUTTON. 



The British Slugs. 



Mr. J. W. T.^VLOR has just published part ii. of his 

 admirable " Monograph of the Land and Freshwater 

 Mollusca of the British Isles," containing a discussion of 

 the slugs of the genus Arion. It is a matter of interest 

 that, notvi^ithstanding the great amount of information 

 gathered in recent years, the beautiful bicoloured varieties 

 of A. ater appear to hold their own as truly endemic 

 inhabitants of Britain. These are three in number, 

 though Mr. Taylor treats the third as merely a sub- 

 variety. 



(i) Arion ater, var. albolateralis. Roebuck, 1883. Back 

 black, sides white. 



(2) Arion ater, var Roebucki {bicolour, Roebuck, in error). 

 Back brown, sides yellow. 



(3) Arion ater, var. Scharffi, Cockerell, 1893. Back black, 

 sides yellow. 



Mr. Taylor retains the name bicolour for the second 

 variety, but it is not the bicolour of Moquin-Tandon, as 

 was formerly supposed, and a new name is necessary. 

 It is appropriate to name it after Mr. Roebuck, who first 

 made it known. These magnificent slugs are of western 

 distribution in the British Islands, and have quite a wide 

 range. The only evidence of their occurrence on the 

 Continent is Scharff's statement that Simroth found speci- 

 mens " similar " to var. Roebucki on the shores of the 

 Baltic ; and the possibility that the Norwegian var. 

 medius, Jensen, may be similar to albolateralis, though it 

 is very likely not even of the same species. A quite 

 different variety of A. ater is the wholly black form ater- 

 rima, said to be especi^ally northern and montane. Accord- 

 ing to Mr. Taylor, this is exclusively British, except that 

 it appears to be represented in Spain and Portugal by a 

 similar animal named hispanicus by Simroth. However, 

 I had always regarded this aterriina variety as the one 

 so described from France by Dumont and Mortillet (c/. 

 Science Gossip, 18S9, p. 212, " the pitchy black variety 

 found in swamps "), and if it is not, the name aterriina, 

 applied to it by Mr. Taylor, cannot stand. At the opposite 

 pole of variation from aferrinia is the brilliant red form 

 A. ater, var. cocciiica (Gistel), which is hardly ever found 

 in England, but is abundant in the warmer and drier 

 regions of Central Europe. 



Incidentally, it may be remarked that the name Arion 

 hortensis, var. subfusca, _employed by Mr. Taylor, cannot 

 be retained, as it is founded on Limax subfuscus, C. Pfr., 

 a homonym of L. subfuscus, Draparnaud. 



T. D. A. Cockerell. 



University of Colorado, June 26. 



