reasonable explanation save that of evolution.

The well-known group of hoofed animals, including horses and cattle, is
also valuable for our present purposes, as well as in a later connection
when the evidence of fossils is described. The elephant possesses five
toes armed with well-developed nails or hoofs. A tapir has four or three
toes, and it would seem that its ancestor had had five toes, of which one
or two had been lost. A rhinoceros possesses three toes, and its foot is
constructed internally like the elephant's with the outer elements absent.
The horse comes last with one large toe and hoof, but on either side of
the main bones of this digit are vestiges of what must have been toes in
its ancestors. Among the even-toed forms the hippopotamus has four which
reach the ground, with a vestige of a fifth, so this animal has apparently
descended from a typical mammal with the full number along a different
line from that taken by the odd-toed forms. A pig has a cloven hoof, made
up of what we may call the third and fourth members of a series of five
digits, but the second and fifth fingers and toes are present, though they
are withdrawn from the ground so as to be no longer functional; this
animal seems to have proceeded further along the same line taken by the
hippopotamus. A deer, with still smaller rudiments at the sides of its
double foot, leads in the comparative series to the camel with a cloven
hoof devoid of any such relics.

We must pass with only brief mention the lower orders of mammalia, like
the insect-eating forms to which armadillos and ant-bears belong. Of
greater interest are the pouched mammals like the kangaroo and opossums,
which live almost exclusively in the Australian realm. The kangaroo is
endowed with a head somewhat like that of a goat, and well-developed hind
legs that enable it to make leaps of astonishing length. Some of its
relatives, such as the bandicoot, are like rats, or like bears, as in the