; other
great groups, including the ducks, cormorants, gulls, penguins, etc.,
are aquatic; while the bulk of the Passerine birds are aerial and
arboreal. The same general facts can be detected in all other classes of
animals. In the mammalia, for example, we have in the common rat a
fish-eater and flesh-eater as well as a grain-eater, which has no doubt
helped to give it the power of spreading over the world and driving away
the native rats of other countries. Throughout the Rodent tribe we find
everywhere aquatic, terrestrial, and arboreal forms. In the weasel and
cat tribes some live more in trees, others on the ground; squirrels have
diverged into terrestrial, arboreal, and flying species; and finally, in
the bats we have a truly aerial, and in the whales a truly aquatic order
of mammals. We thus see that, beginning with different varieties of the
same species, we have allied species, genera, families, and orders, with
similarly divergent habits, and adaptations to different modes of life,
indicating some general principle in nature which has been operative in
the development of the organic world.
Pages:
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204