allied allied 1872 | closely allied 1859 1860 1861 1866 | closely-allied 1869 |
species; species; 1872 | species 1859 1860 1861 1866 1869 |
...OMIT 1872 |
of the same genus; 1859 1860 1861 1866 1869 |
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. |
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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. 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,
....... 1872 | or 1859 1860 1861 1866 1869 |
to collect food more quickly, or, as there is reason to believe,
to lessen to lessen 1872 | by lessening 1859 1860 1861 1866 1869 |
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
possible possible 1872 | natural 1859 1860 1861 1866 1869 |
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. |
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Now look at the Galeopithecus or
so-called flying so-called flying 1872 | flying 1859 1860 1861 1866 1869 |
lemur, which formerly was
....... 1869 1872 | falsely 1859 1860 1861 1866 |
ranked amongst
bats, but is now believed to belong to the Insectivora. bats, but is now believed to belong to the Insectivora. 1872 |
bats. 1859 1860 1861 1866 1869 |
An An 1872 |
It has an 1859 1860 1861 1866 1869 |
extremely wide
flank-membrane flank-membrane 1872 | flank-membrane, 1859 1860 1861 1866 1869 |
stretches stretches 1872 | stretching 1859 1860 1861 1866 1869 |
from the corners of the jaw to the tail, and
includes includes 1872 | including 1859 1860 1861 1866 1869 |
the limbs
with with 1872 | and 1859 1860 1861 1866 1869 |
the elongated
fingers. fingers. 1872 | fingers: 1859 1860 1861 1866 1869 |
....... 1872 | the 1859 1860 1861 1866 1869 |
....... 1872 | flank membrane 1859 | flank-membrane 1860 1861 1866 1869 |
....... 1872 | is, 1859 1860 1861 1866 1869 |
....... 1872 | also, 1859 1860 1861 1866 1869 |
....... 1872 | furnished 1859 1860 1861 1866 1869 |
....... 1872 | with 1859 1860 1861 1866 1869 |
....... 1872 | an 1859 1860 1861 1866 1869 |
....... 1872 | extensor 1859 1860 1861 1866 1869 |
....... 1872 | muscle. 1859 1860 1861 1866 1869 |
This flank-membrane is furnished with an extensor muscle. Although no graduated links of
structure, structure, 1859 1860 1861 1866 1872 | struc- ture, 1869 |
fitted for gliding through the air, now connect the Galeopithecus with the other
Insectivora, Insectivora, 1872 | Lemuridæ, 1859 1860 1861 1866 1869 |
yet
there is there is 1869 1872 |
I can see 1859 |
I see 1860 1861 1866 |
no difficulty in supposing that such links formerly existed, and that each
was developed in was developed in 1872 |
had been formed by 1859 1860 1861 1866 1869 |
the same
manner manner 1872 | steps 1859 1860 1861 1866 1869 |
as
with with 1872 | in 1859 1860 1861 1866 1869 |
the
...OMIT 1872 |
case of the 1859 1860 1861 1866 1869 |
less perfectly gliding squirrels;
....... 1872 | and that 1859 1860 1861 1866 1869 |
each grade of structure
having been having been 1872 | had been 1859 | was 1860 1861 1866 1869 |
useful to its possessor. Nor can I see any insuperable difficulty in further believing
....... 1872 | it possible 1859 1860 1861 1866 1869 |
that the
membrane connected membrane connected 1872 | membrane-connected 1859 1860 1861 1866 1869 |
fingers and
fore-arm fore-arm 1859 1872 | forearm 1860 1861 1866 1869 |
of the Galeopithecus might
have been have been 1872 | be 1859 1860 1861 1866 1869 |
greatly lengthened by natural
selection. selection. 1872 | selection; 1859 1860 1861 1866 1869 |
and this, as far as the
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