392 
DARWINISM 
CHA1>. 
any kind of special creation, or by sudden advances of organisa¬ 
tion in the offspring of preceding types, such close relationship 
would not be found ; and facts of this kind become, therefore, 
to some extent a test of evolution under natural selection or 
some other law of gradual change. Of course the relationship 
will not appear when extensive migration has occurred, by 
which the inhabitants of one region have been able to take 
possession of another region, and destroy or drive out its 
original inhabitants, as has sometimes happened. But such 
cases are comparatively rare, except where great changes of 
climate are known to have occurred ; and we usually do find 
a remarkable continuity between the existing fauna and flora 
of a country and those of the immediately preceding age. A 
few of the more remarkable of these cases will now be briefly 
noticed. 
The mammalian fauna of Australia consists, as is well 
known, wholly of the lowest forms—the Marsupials and Mono- 
tremata—except only a few species of mice. This is accounted 
for by the complete isolation of the country from the Asiatic 
continent during the whole period of the development of the 
higher animals. At some earlier epoch the ancestral mar¬ 
supials, which abounded both in Europe and North America 
in the middle of the Secondary period, entered the country, 
and have since remained there, free from the competition of 
higher forms, and have undergone a special development in 
accordance with the peculiar conditions of a limited area. 
While in the large continents higher forms of mammalia have 
been developed, which have almost or wholly exterminated the 
less perfect marsupials, in Australia these latter have become 
modified into such varied forms as the leaping kangaroos, the 
burrowing wombats, the arboreal phalangers, the insectivorous 
bandicoots, and the carnivorous Dasyuriche or native cats, 
culminating in the Thylacinus or “ tiger-wolf ” of Tasmania— 
animals as unlike each other as our sheep, rabbits, squirrels, 
and dogs, but all retaining the characteristic features of the 
marsupial type. 
Now in the caves and late Tertiary or Post-Tertiary deposits 
of Australia the remains of many extinct mammalia have been 
found, but all are marsupials. There are many kangaroos, 
some larger than any living species, and others more allied to 
