28 THE SEPOET OP THE No. 36 



mining the distribution of the species. The water-snails are largely dependent upon 

 the river system that they inhabit, different river-systems usually have distinctive 

 faunas, while terrestrial forms are practically uninfluenced by this factor. Strong, 

 high-flying insects and birds will not be deterred by many barriers that would be 

 prohibitive to flightless forms and weak fliers. 



For such reasons of these it is. impossible to construct a map of the zoological 

 regions of the world or of any country that will suit all groups of animals equally 

 well. There have been, however, certain events in the world's history that have had 

 a vast effect on the distribution of life in general over immense areas of land. As 

 far as Canada is concerned, the great geological events of comparatively recent date 

 have been the Ice Age and the existence of former land-bridges connecting North 

 America with Asia and Europe. 



The existence of a land-bridge across Bering's Sea in early Glacial times is 

 supported by many facts of geology and zoogeography. The close resemblance 

 between the fauna and flora of North- western North America and North-eastern 

 Asia has often been remarked upon, and it is generally admitted that a large propor- 

 tion of the species of both plants and animals inhabiting the North-west originally 

 came from Asia over this land-bridge. Many of these species have since spread east- 

 ward and now range across the continent, but the number of such species is noticeably 

 greater in the "West, particularly in Alaska, than elsewhere. It is noteworthy, too, 

 that such species, among the mammals at least, are absent from Newfoundland, 

 which was separate from the continent even at the time of the invasion of animals 

 from Asia. Thus the moose, wapiti and barren-ground bear, which are of Old World 

 stock, range across Canada, but do not occur in Newfoundland, while the mountain 

 sheep, whose nearest relatives are also Asiatic, do not range east of the Rockies, even 

 as a fossil. The same is true of the butterflies of the genus Parnassius and many 

 other insects.. 



The existence of a land-bridge connecting North America and Europe by way 

 of Greenland, Iceland and Scotland, is also supported by the fact that the fauna 

 and flora of Greenland are mixtures of American and European species, some of 

 the latter, such as the European garden-snail, Helix hortensis, ranging down the 

 east coast of North America as far as Maine, but not penetrating westward. The 

 noctuid moths, Anarta schoenherri and A. lapponica, occur in Scandinavia, Green- 

 land and Labrador, while A. melanopa is found in Colorado, the AAHiite Mountains, 

 Labrador, Scandinavia, Scotland and the Alps. 



These former land connections existed at a time when conditions were more 

 favourable for life in the north than they are at the present time. Hence a large 

 number of species, which formerly inhabited the far north have since been driven 

 southward into more hospitable latitudes, and no longer occur in the Arctic regions. 



On the other hand, there is no doubt that, at some time in the past, arctic 

 conditions as we now understand them existed much farther south in North America 

 than they do at the present time. We find isolated remnants of arctic and subarctic 

 faunas and floras hundreds of miles to the south of their present general area of 

 distribution. The summit of Mount Washington supports a number of species of 

 plants and animals which occur elsewhere only in the Arctic regions. Oeneis semidea 

 ■ is the classical example among insects. The White Mountain colony of this butterfly 

 is separated by a thousand miles from its nearest brethren in Labrador. 



The presence of these southern remnants of the Arctic fauna and flora is usually 



attributed to the influence of the Glacial Period. This was a period during which it 



is commonly believed that almost the whole of the northern half of North America 



- as well as a large part of Europe and Asia became covered with an almost continuous 



