CHAPTER XI. 
THE GEOGRAPHICAL DISTRIBUTION OF ANI- 
MALS. 
THE assemblage of animal life peopling any one locality 
or area is called its fauna, as the plants of a place consti- 
tute its flora. Where the physical geography—i.e., the con- 
tour of the surface, the plains, valleys, and hills—is of iden- 
tical character and the climate the same, the fauna is much 
the same, but when these characteristics of soil and climate 
change, as in passing from lowlands to highlands, or from 
south to north, the assemblage of animals will be found 
to change in a corresponding ratio. And as there are no 
definite limits to any large area of the earth’s surface, the 
physical features of one area merging insensibly, as a rule, 
into adjoining districts, so adjoining faune merge into one 
another, and a certain proportion of the species may range 
through two or more faunal areas. 
There are in nature causes tending to restrain animals 
within their faunal limits, and others tending to diffuse 
them, or to cause them to migrate from their specific cen- 
tres or centres of creation—namely, the point where the in- 
dividuals of a species are most abundant, and where, ac- 
cordingly, they are supposed to have originated. 
Barriers to the Spread of Animals from their Specific 
Centres.—Among the most important are the oceans and 
their basins. The animals of the opposite sides of the Pa- 
cific Ocean are entirely unlike, no species being common to 
the two sides; while, of the immense numbers of animals 
peopling the coast of Brazil and the opposite coast of Af- 
rica, only two or three are known to be identical. Differ- 
ence in climate is also a great barrier, the animals of the 
