96 GEOGRAPHICAL DISTRIBUTION 
and the Continent, which is shown by geological evidence to have 
actually been the case. 
The above instances are sufficient to show what an important 
influence the date of separation of islands from the adjacent 
continents has had upon their existing mammalian fauna, and how 
largely the present distribution of mammalian life is bound up with 
the past history of our globe. We must, however, not omit to 
mention another very important agency of past times which has 
likewise had great influence on the present distribution of the 
various faunas of the northern hemisphere. This is the so-called 
glacial epoch, which took place immediately before the establish- 
ment of the present condition of things, and appears to have been 
the cause of the extinction of many of the larger mammalian types 
which formerly inhabited Europe, and whose retreat to the warmer 
regions of the south was apparently cut off by the Mediterranean. 
Zoological Regions.—Zoologists are now generally agreed in dividing 
the land surfaces of the globe into a number of zoological regions or 
provinces, characterised by a more or less distinctly marked general 
Jacies of their fauna asa whole. Some of these regions are much more 
distinctly defined than the others; and in the majority of cases 
there is a kind of neutral ground or No-man’s-land at the junction 
between any two of these regions. It must also be remembered 
that in the Old World proper as we go back in time we find a 
gradual assimilation in the mammalian faunas of the different 
regions, indicating that originally there was one large fauna of 
a generally similar type occupying the greater portion of this 
area. Thus we find that Hippopotami, Giraffes, Kudus, Elands, 
and other types of Antelopes now restricted to Africa, formerly 
extended to Europe and India, while there is also evidence to show 
that the group of large anthropoid Apes, now found only in Africa 
and the Bornean region, were likewise spread over a large part of 
the south-western half of the Old World. Moreover, while at the 
present day there is a marked connection between the mammals of 
the northern regions of both the Old and New Worlds, in the 
Tertiary period it appears that the fauna of the whole of North 
America was much more nearly allied to that of the central regions 
of the Old World than is now the case. Thus in the Tertiary 
rocks of America we meet with remains of what we are accustomed 
to regard as such essentially Old World genera as Horses and 
Rhinoceroses. On the other hand there are no traces in America 
of the existence at any period of Apes, Giraffes, Hippopotami, or 
Hyznas, while that continent has yielded evidence of groups of 
Ungulates totally unrepresented in the eastern hemisphere. 
The chief zoological regions of the globe, proposed by Mr. Sclater 
in 1857, and now recognised by the majority of authorities, are 
six in number, and are named as follows. Firstly, the Palearctic 
