fore limb is again like that of the cat's leg, although the whole
structure is a flexible finlike paddle. The hind limb has disappeared as
an efficient organ, but the significant fact is that small rudiments of
hind limbs are present just where corresponding structures are placed in
the seal. These vestiges cannot be reasonably accounted for, 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