ON COLLEMBOLA FROM THE SOUTH ORKNEY ISLANDS. 57 



DISTRIBUTIONAL NOTES. 



As mentioned in the introduction to this paper, the existence of identical or of 

 nearly allied species of Collembola on widely separated areas may be regarded as strong 

 evidence for ancient land-connections between those areas. Many recent writers on 

 zoological geography have expressed belief in a former extension of the Antarctic 

 continent, wide enough to connect with America, Africa, and Australia. A full 

 discussion of the problem has recently been given in Ortmann's valuable paper (1904, 

 pp. 310-324, with map, pi. xxxix. ) on the Tertiary invertebrate fauna of Patagonia, 

 and there can be no doubt that the trend of modern speculation is against the doctrine 

 of the permanence through past ages of the great ocean basins of the present day, as 

 upheld in the classical writings of DARWIN and WALLACE. HUTTOX, who many years 

 ago suggested the Antarctic continent as a former means of communication between 

 Australia and Patagonia, and subsequently withdrew the hypothesis in favour of a 

 trans-Pacific continent, has now reaffirmed his former belief (1905), laying special 

 stress on the Collembola of South Victoria Land as evidence for the former connection 

 of that remote region with the northern continents. 



From the facts established in the present paper, further support for the ancient 

 extension of Antarctica may be readily drawn. The existence of the genus Cryptopygus 

 and of the species Isotoma octo-oculata on the South Orkneys as well as on Danco Land, 

 together with the presence of the Isotoma on Kerguelen, point to the former existence 

 of extensive land-tracts south of the American continent, with connection, either by 

 way of Antarctica or of South Africa, to Kerguelen. It cannot indeed be inferred from 

 the distribution of these springtails that there was at any one period a continuous land- 

 surface from Patagonia and Graham Land to Kerguelen. But it can hardly be denied 

 that the insects must have travelled overland, though the land-connections may have 

 varied in extent, and become broken at different points during different periods. The 

 bathymetrical work of the Scotia Expedition, as set forth by Bruce (1905), demonstrat- 

 ing a continuous bank, less than 2000 fathoms beneath the surface of the South 

 Atlantic, stretching eastwards from the South Orkneys towards South-East Africa, 

 makes the former existence of one such land-tract the more credible. And the geo- 

 logical structure of the South Orkneys leaves no doubt that they must be regarded as 

 strictly " continental " islands. Similarly, the " Kerguelen plateau," as mapped by the 

 explorers of the Valdivia (ScnoTT, 1902), renders in the highest degree probable the 

 former union of Kerguelen with Antarctica ; and a connection thence to South Africa is 

 not impossible of acceptance. 



If, as we believe, these springtails apparently members of a typically Antarctic 

 fauna owe their presence on the islands that they now inhabit to a former extension 

 of the Antarctic continent, they must be of a considerable geological age. ORTMANN 

 (1904) considers that the greatest extension of Antarctica existed in the Cretaceous and 

 Eocene eras. HUTTON (1905) argues for the Jurassic as the period of most extensive 



(ROY. soc. OF EDIN. PKOC., VOL. sxvi., PP. 478-479.) 



