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. We cannot doubt that each structure is of use to each kind of squirrel in its own country, by enabling it to escape birds or beasts of prey,
or or 1859 1860 1861 1866 1869 | or 1872 |
to collect food more quickly, or, as there is reason to believe,
by lessening by lessening 1859 1860 1861 1866 1869 | to lessen 1872 |
the danger from occasional falls. But it does not follow from this fact that the structure of each squirrel is the best that it is possible to conceive under all
natural natural 1859 1860 1861 1866 1869 | possible 1872 |
conditions. Let the climate and vegetation change, let other competing rodents or new beasts of prey immigrate, or old ones become modified, and all analogy would lead us to believe that some at least of the squirrels would decrease in numbers or become exterminated, unless they also became modified and improved in structure in a corresponding manner. Therefore, I can see no difficulty, more especially under changing conditions of life, in the continued preservation of individuals with fuller and fuller flank-membranes, each modification being useful, each being propagated,
until, until, 1866 1869 1872 | until 1859 1860 1861 |
by the accumulated effects of this process of natural selection, a perfect so-called flying squirrel was produced. |
|
Now look at the Galeopithecus or
flying flying 1859 1860 1861 1866 1869 | so-called flying 1872 |
lemur, which formerly was
....... 1869 1872 | falsely 1859 1860 1861 1866 |
ranked amongst
bats. bats. 1859 1860 1861 1866 1869 |
bats, but is now believed to belong to the Insectivora. 1872 |
It has an It has an 1859 1860 1861 1866 1869 |
An 1872 |
extremely wide
flank-membrane, flank-membrane, 1859 1860 1861 1866 1869 | flank-membrane 1872 |
stretching stretching 1859 1860 1861 1866 1869 | stretches 1872 |
from the corners of the jaw to the tail, and
including including 1859 1860 1861 1866 1869 | includes 1872 |
the limbs
and and 1859 1860 1861 1866 1869 | with 1872 |
the elongated
fingers: fingers: 1859 1860 1861 1866 1869 | fingers. 1872 |
the the 1859 1860 1861 1866 1869 | the 1872 |
flank-membrane flank-membrane 1860 1861 1866 1869 | flank-membrane 1872 | flank membrane 1859 |
is, is, 1859 1860 1861 1866 1869 | is, 1872 |
also, also, 1859 1860 1861 1866 1869 | also, 1872 |
furnished furnished 1859 1860 1861 1866 1869 | furnished 1872 |
with with 1859 1860 1861 1866 1869 | with 1872 |
an an 1859 1860 1861 1866 1869 | an 1872 |
extensor extensor 1859 1860 1861 1866 1869 | extensor 1872 |
muscle. muscle. 1859 1860 1861 1866 1869 | muscle. 1872 |
↑1 blocks not present in 1859 1860 1861 1866 1869; present in 1872 | This flank-membrane is furnished with an extensor muscle.
|
Although no graduated links of
struc- ture, struc- ture, 1869 | structure, 1859 1860 1861 1866 1872 |
|