Look at the Mustela
vison of North America, which has webbed feet, and which resembles an otter
in its fur, short legs, and form of tail; during summer this animal dives
for and preys on fish, but during the long winter it leaves the frozen
waters, and preys, like other polecats on mice and land animals. If a
different case had been taken, and it had been asked how an insectivorous
quadruped could possibly have been converted into a flying bat, the
question would have been far more difficult to answer. Yet I think such
difficulties have little weight.
Here, as on other occasions, I lie under a heavy disadvantage, for, out of
the many striking cases which I have collected, I can give only one or two
instances of transitional habits and structures in allied species; and of
diversified habits, either constant or occasional, in the same species.
And it seems to me that nothing less than a long list of such cases is
sufficient to lessen the difficulty in any particular case like that of the
bat.
Look at the family of squirrels; here we have the finest gradation from
animals with their tails only slightly flattened, and from others, as Sir
J. Richardson has remarked, with the posterior part of their bodies rather
wide and with the skin on their flanks rather full, to the so-called flying
squirrels; and flying squirrels have their limbs and even the base of the
tail united by a broad expanse of skin, which serves as a parachute and
allows them to glide through the air to an astonishing distance from tree
to tree.
Pages:
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279