r, unless they
are the degenerate hinder limbs of a remote four-footed ancestor.
Furthermore the unborn whale possesses a complete coat of hair, which is
afterwards replaced by blubber; but hair is a thatchlike coat to shed
rain, as the way the hairs lie on a terrestrial mammal indicates. We are
therefore forced to conclude that whales have originated from four-footed
animals walking about on land, because no opposed explanation gives so
reasonable an interpretation of the observed facts.

Another group of familiar animals materially reinforces the results
already established. After what has been said, it will not be difficult to
perceive the meaning of the resemblances among mice of the house and
field, and of rats and rabbits and squirrels. All of them possess heavy
curved gnawing teeth, or incisors, and lack the flesh-tearing or canine
teeth. They agree in many other respects which distinguish them as a
separate natural order of the mammals called the rodentia. Again we find a
highly aberrant form in the flying squirrel, which leads toward an order
with another plan of body. This animal is a true rodent, which lengthens
its leap from branch to branch by means of a fold of skin stretching
between its fore and its hind limbs. It is an animated aeroplane, and it
shows in part how bats have originated. The wing of a bat is an elastic
membrane stretching not only between the two legs of one side, but also
between the greatly lengthened "fingers" of the fore limb. But the bones
of arm, wrist, and fingers are almost precisely the same in number and
relation as in walking forms. The fact that this peculiar wing adheres to
a plan belonging to the anterior legs of walking or climbing types has no
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