The relationship between the palaearctic and nearctic faunas 



269 



90' 80' W to" SO' tO'iO'^O'lO' 0" 10' JO" 30' fO' 50' 60' 70' ^ 



FIG. 42. Wind-drift of Fieldfares {Turdiis pilaris L.) to 

 Greenland in January, 1937. 



Black circles = observed specimens. Broken line = prob- 

 able course of flight. 



Unbroken line = isobars of January 19 1937 (at 7 p.m.). 

 Arrows = wind direction. 

 (From Salomonsen, 195 i). (From Rosenberg, Faglar i Sverige.) 



A similar calculation, and with similar results, was carried out on the Collemboles 

 of Iceland and the Faeroes (Lindroth, 193 1, p. 516). 



The accidental nature of introduction is thus clearly demonstrated. If this 

 holds true for the unquestionably imported species with a more or less pronounced 

 synanthropic habitat, how much more due to chance would not human transport 

 be of species indifferent to or rather avoiding the neighbourhood of man! Yet 

 within this latter faunal element the species common to the North Atlantic islands 

 are more, not less numerous. This is the clearest possible proof that their presence 

 is not due to human agencies. 



We have thus rejected the idea that the pronouncedly European character of 



