NOTICES OF NEW BOOKS. 69 
Tt would be impossible, within the limited space at our disposal, 
to discuss in detail the different subjects dealt with in the twenty- 
three chapters into which the work is divided, and we must content 
ourselves with presenting to our readers a faint outline of the 
general argument. 
Mr. Wallace is of opinion that the existing continents and 
deep oceans are of great geological antiquity; that during the 
eocene period the bulk of the land was on the northern side 
of the Equator; and that in that hemisphere the struggle for 
existence was more severe than in the southern hemisphere. Con- 
sequently the highest and most specialized forms of animal life are 
to be found north of the Equator. In supporting his views, with 
much sound reasoning, Mr. Wallace has adopted the six zoological 
regions first proposed by Mr. Sclater in 1857, and these are now 
generally accepted as natural divisions of the earth’s surface. With 
the exception that Mr. Sclater’s Indian Region is altered by Mr. 
Wallace, in name only, to the Oriental Region, no other important 
change is suggested. The six regions accordingly stand as the 
Palearctic, the Ethiopian, the Oriental, the Australian, the Nearctic, 
and the Neotropical; each being divided into four subregions. 
The only subregion in which no mammals exist, except Bajs, 
is New Zealand; and Mr. Wallace explains this fact by supposing 
that New Zealand has not been connected with any other part of 
the earth’s surface since the creation of the Mammalia. The 
great region of Australia is almost destitute of placental mammals, 
showing, according to our author, a very ancient isolation of that 
part of the world. 
The various cases of the existence of isolated forms in South 
America and South Africa are also explained by the supposition 
that these regions, separated in remote geological times, were 
large islands, and the struggle for existence there not having been 
so severe as in the northern hemisphere, low forms of J/ammalia, 
such as the Edentata, Caviide, and others have survived to the 
present day. Weare very much disposed to accept this reasoning, 
and it well explains the existence of such low forms of birds as 
Apteryx in New Zealand, the Tinamide, Dicholophus, and others 
in South America, Rhinochetus in New Caledonia, and such an 
aberrant form of the Accipitres as Serpentarius in Africa. 
In the opinion of Mr. Wallace, the present state of the globe is 
one of zoological depauperization, caused by the glacial period. 
