286 CHAPTER III 



scattered relict occurrences (Hydromantes, Umbra, &c.), usually a step towards 

 extinction, do not necessarily imply earlier connection at shortest distance, the 

 fossils "often showing us the contrary. 



It is questionable if, from the stand-point of a biologist, there is any need at all 

 for transatlantic land-connection in any geological period. Simpson, on palaeo- 

 zoological evidence, first (1940, p. 149) postulated "the inference of a wide-open 

 corridor" between Europe and North America in the Lower Eocene but later 

 (1947, pp. 658-659, 666, Footnote) regarded a substituting Pacific connection 

 during this period as at least equally probable. 



Whether the theory of continental drift is true, is a problem for geologists 

 and geophysicians. The only contribution that can be delivered by a biogeographer 

 is the declaration that, at least as far as the North Atlantic area is concerned, the 

 continental drift, if considered a reality, took place in so early a period that its 

 biological consequences cannot be traced. Also, the annual rate of drift supposed 

 by Wegener for the North Atlantic is extravagantly high (Zeuner, 1950, p. 355). 



Circumpolar animals 



The word "Circumpolar" should not be interpreted too literally. No animal 

 species inhabits all continents and islands surrounding the North Pole. The 

 concept is here used to cover species occurring in the northern parts of Europe, 

 Asia and North America without conspicuous interruptions of area. The term 

 "Holarctic" is not a synonym because it only means that a species is indigenous 

 in both the Palaearctic and the Nearctic region, without any demand for continuity. 

 Yet all Circumpolar species are, of course, Holarctic at the same time. 



Another question is how pronounced northerly a species' area is bound to be 

 in order to be called Circumpolar. The "Circumtropical" species, such as the Dra- 

 gonfly Pantala flavescens F. (Rensch, 1950, p. 136, fig. 109), must be excluded. 

 A subtropical animal distributed round the earth at least belongs to either Hemi- 

 sphere and may be included here, but the instances of this geographical type are 

 so few that their placing has almost no interest. 



As a matter of fact, the zonation of the circumpolar species from north to south, 

 as well as vertically in the mountains, reveals interesting features. Carabid beetles 

 are sufficiently known in this respect to serve as an illustration. The distribution 

 of the 45 known circumpolar species among the vegetation belts as defined by 

 Scandinavian botanists {vide Lindroth, 1949, p. 436-448), and corresponding 

 zones of Asia and North America, is shown in table 8. 



The table 8 gives clear evidence that the subarctic (subalpine) region contains 



