58 PROFESSOR GEORGE H. CARPENTER 



land in southern regions. We may safely conclude that Cryptopygus and Isotoma 

 octo-oculata have survived throughout the Tertiary epoch at least, with comparatively 

 little change of structure. 



The affinities of Isotoma Brucei open up a problem of even greater interest. It is 

 closely allied, as we have seen, to /. Beselsii, a springtail which has been found in 

 Spitzbergen, Jan Mayen Island, Scotland (shores of the Firth of Forth), Greenland 

 (Polaris Bay), and Massachusetts. We cannot doubt that this affinity points to a 

 former connection between the Antarctic continent, of which the South Orkneys once 

 formed part, and the northern continents. The presumption seems that this connection 

 was by way of America, and the distribution of some allied springtails supports this 

 presumption.* The common European Isotoma palustris, Miiller, occurs both in North 

 and South America ; and SCHAFFER (1897) has described an Isotoma /. obtusicauda 

 from Valparaiso, closely allied to two peculiar northern species, /. crassicauda, Tullberg, 

 and /. littoralis, Delia Torre. These last-mentioned insects come nearer than any 

 other species of Isotoma to /. Brucei and /. Beselsii, agreeing with them in the evident 

 position of the spring on the fourth abdominal segment, but differing in the absence of 

 prominent teeth on the mucrones. We find, therefore, that these groups of springtails, 

 considered until a few years ago characteristically Arctic and sub- Arctic, are represented 

 in the Andean sub-region of South America, in Tierra del Fuego, and in the distant 

 South Orkney Islands. 



Must /. Brucei, with its northern affinities, be regarded as an older or a newer 

 member of the South Orcadian fauna than the distinctively Antarctic species that share 

 its present home ? Northern species, at or beyond the southern limits of the present 

 American continent, must be either comparatively recent immigrants Pliocene or 

 later or else carry us back to early Mesozoic times ; for the existence of some sea- 

 channel across America, checking migration from north to south, during the Cretaceous 

 and Early Tertiary periods, is generally admitted. VON JHERING, for example, lays 

 stress (1891) on the faunistic distinction between southern and northern South 

 America, and suggests the existence in Secondary and Early Tertiary times of two 

 continents an "Archiplata" connected with Antarctica, and an " Archicguyana " con- 

 nected by an Atlantis with West Africa. Now it seems unlikely that /. Brucei can be 

 a late Tertiary immigrant into the Antarctic regions. The necessary connection of the 

 South Orkneys with Patagonia can hardly have lasted late enough. And the group to 

 which the species belongs is a primitive group even of this comparatively primitive 

 genus and order. In these insects, as mentioned above, the spring evidently belongs to 

 the fourth abdominal segment, whereas in most species of the genus and family it is 

 apparently borne on the fifth. WILLEM (1900) has shown, however, that in reality it 

 always belongs to the fourth. Thus we see that in the group of /. Brucei an ancient 

 character has been retained, and the shore-haunting habit of all the species belonging to 



* Which receives unexpected confirmation from WAHLGREN'S discovery (1906) of /. Beselsii in Tierra del 

 Fuego. 



(HOY. soc. OF EDIN. PHOC., VOL. xxvi., PP. 479-481.) 



