14 INTRODUCTION 



of asexual reproduction, they may in part be more suited for a passive dispersal 

 across the sea. 



The following attempt to estimate the faunal exchange between Europe and 

 North America had to be based on suffficient comparative knowledge of the 

 taxonomy of the forms occurring in the two continents. Unfortunately, such a 

 happy state of affairs has been reached in only few groups of animals. European 

 and American zoologists are too inclined to work independently and a taxonomic 

 study of a certain species group, to be useful in zoogeography, must be carried out 

 by a specialist fully acquainted with both of the faunas. An attempt to compile a 

 "complete" list of terrestrial (and limnic) animals common to Europe and North 

 America would therefore be a hopeless enterprise. It was necessary to restrict the 

 task to groups of animals which may be regarded as sufficiently worked through 

 and to add some cases of special interest from other groups. 



Marine animals and animals of the tidal zone were excluded from the investiga- 

 tion. 



The bias of this study is also accentuated by the fact that the discussion often 

 starts, taxonomically from Carabid beetles, geographically from Newfound- 

 land. As an apology it may be pointed out that the insect family mentioned pro- 

 vides an unusually suitable subject to a student in zoogeography: (i) it is numerous 

 in species, especially in northern regions; (2) these usually possess good specific 

 and subspecific characters, above all in the male genitalia; (3) many species show 

 a marked geographic variation; (4) the means of dispersal are unusually varying, 

 many species being constantly short-winged, bound to the soil and conservative 

 in distribution, others constantly long-winged, flying more or less regularly, 

 whereas, in a third category, both long- and short-winged individuals occur which 

 often results in a characteristic pattern of distribution of the two forms; (5) finally, 

 the taxonomy of northern Carabidae is tolerably well-known in both continents. 

 —As regards Newfoundland, this island has a key position in the understanding of 

 the human transatlantic transport of animals and plants. 



