366 GEOGRAPHIC DISTRIBUTION OF LIFE IN NORTH AMERICA. 
Thus primeval man, and in truth the ancestors of primeval man, 
learned by observation the great fact of geographic distribution, the 
fact that particular kinds of animals and plants are not uniformly dif- 
fused over the earth, but are restricted to more or less circumscribed 
areas. 
It will be observed that two classes of cases are here referred to, 
namely, (1) cases in which in the same general region certain species 
are restricted to swamps or lowlands, while others are confined to dense 
forests or rocky hillsides—difterences of station, and (2) cases in which, 
regardless of local peculiarities, a general change takes place in the 
fauna and flora in passing from one region to another, or from low val- 
leys or plains to high mountains—geographic differences, The latter 
class only is here considered. 
Every intelligent school-boy knows that elephants, lions, giraffes, and 
chimpanzees inhabit Africa; that orangs and flying lemurs live in 
Borneo; kangaroos in Australia; the apteryx in New Zealand; the 
Royal Bengal tiger in India; Hamas, chinchillas, and sloths in South 
America; the yak in the high table lands of Thibet, and soon. In 
accordance with these facts naturalists long ago began to divide the 
surface of the globe into zodlogical and botanical regions irrespective 
of the long-recognized geographic and political divisions.* It was 
found that different degrees of relationship exist between the indige- 
nous animals and plants of different countries, and that as a rule the 
more remote and isolated the region and the earlier in geologic time its 
separation took place, the more distinct were its inhabitants from those 
of other regions. Each of the larger islands lying near the equator 
and the continental masses of the southern hemisphere were found to 
possess not only peculiar species and genera, but even families and 
orders not found elsewhere; and it was discovered that insular areas 
of considerable magnitude that have had no land connection with other 
areas since very early times possess faunas and floras remarkable for 
the antiquity of their dominant types. In Australia, the most discon- 
nected of all the continents, the entire mammalian fauna, though won- 
derfully diversified in appearance and habits, belongs to the primitive 
orders of monotremes and marsupials, whose best known representa- 
tives are the duck-billed platypus and the kangaroo. In the latter 
group Australia and neighboring islands contain no less than six fami- 
lies not found in any other part of the world. 
Madagascar is the exclusive home of the remarkable aye-aye (Chi 
romys) and Cryptoprocta, the latter believed to be intermediate between 
the cats and civets. 
* Among the many distinguished naturalists who have contributed to the litera- 
ture of the subject may be mentioned Humboldt, Bonpland, Buffon, De Candolle, 
Schouw, Engler, Agassiz, Baird, Asa Gray, Grisebach, Huxley, Gill, Allen, Wallace, 
and Packard. 
