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datable ground. Indeed, the fauna of much of the west coast 
of America, especially that of California and Chili, exhibits 
such marked affinities with that of the Palsearctic region, that 
these countries have been regarded by some writers rather as 
outlying districts of the latter than as biological portions of the 
continents to which they actually belong. It is also to be 
observed that this division of the world into six main regions is 
more applicable to some groups of animals and plants than to 
others. Various attempts have been made to subdivide the 
regions, but though some subdivisions, such as the Mediter- 
ranean subregion, are eminently natural, our knowledge of the 
natural productions of most of the regions is not yet sufficiently 
exact to allow of their being divided in such a manner as to 
gain the general assent of naturalists. 
Owing to the much greater competition of rival forms in 
large continents, the larger and more highly developed forms 
always appear to have originated and been brought to relative 
perfection on the greatest continuous districts of land. But 
notwithstanding the frequent alterations of level during geolo- 
gical ages, which have constantly united or separated various 
portions of the earth’s surface, yet it appears that the largest 
masses of land, though differing in outline and continuity, have 
always occupied nearly the same places ; that is, it is more 
probable that the contour of former continents has been 
changed by gradual increase or diminution, than that a whole 
continent should be submerged or elevated de novo. It also 
appears that the northern hemisphere, and more especially the 
Palsearctic region, has been the birthplace of most of the prin- 
cipal groups of animals, including those now confined to tro- 
pical Africa, or even to South America.* Nor need this 
surprise us, poor as is the present Palsearctic region, when we 
consider the great vicissitudes to which this region has been 
more especially exposed, and the many conditions unfavourable 
to animal life which it now presents. There is little doubt 
that the amazingly rich fauna possessed by Europe previous 
to the glacial epoch was then almost entirely swept out of it, 
a very large proportion of its original fauna and flora being 
either wholly exterminated or driven into distant regions, 
whence, on the abatement of the cold, their descendants would 
return very slowly, if at all. Besides, it is urged by Mr. Belt 
that during the glacial period such vast masses of water were 
locked up in snow and ice that the average level of the sea 
* This is confirmed even by groups of which very few fossil remains 
exist. Mr. S. H. Scudder, in his recent work on fossil butterflies, only 
admits nine species, all European; but of these four are preponderatingly 
American in their affinities, three Oriental, one Mediterranean, and one 
African. 
