| → terms, varieties, species, genera, families, &c.; and we have to discover the lines of descent by the most 1869 1872 |
| most 1859 1860 1861 1866 |
|
| → whatever they may be and of however slight 1869 1872 |
| however slight their 1859 1860 1861 1866 |
|
| → the 1869 1872 |
| the same in the 1859 1860 |
| similar in the 1861 1866 |
|
| → in the leg 1869 1872 |
| leg 1859 1860 1861 1866 |
|
| → intelligible 1859 1860 1861 1866 1869 |
| to a large extent, intelligible 1872 |
|
| → aboriginally alike in an 1869 1872 |
| alike in the 1859 1860 1861 1866 |
|
| → of these classes. 1869 1872 |
| class. 1859 1860 1861 1866 |
|
| → reduced 1869 |
| tend to reduce an 1859 1860 1861 1866 |
| have reduced 1872 |
|
| → they have become useless under 1869 |
| it has become useless by 1859 1860 1861 1866 |
| rendered useless under 1872 |
|
|
by the
→terms, varieties, species, genera, families, &c.; and we have to discover the lines of descent by the most
permanent
→whatever they may be and of however slight
vital
|
|
| The
of bones
→the
hand of a man, wing of a bat, fin of
porpoise, and leg of the horse,— the same number of vertebræ forming the neck of the giraffe and of the elephant,— and innumerable other such facts, at once explain themselves on the theory of descent with slow and slight successive modifications. The similarity of pattern in the wing and
→in the leg
of a bat, though used for such different purpose,— in the jaws and legs of a crab,— in the petals, stamens, and pistils of a
is
→intelligible
on the view of the gradual modification of parts or organs, which were
→aboriginally alike in an
early progenitor
each
→of these classes. On the principle of successive variations not always supervening at an early age, and being inherited at a corresponding not early period of life, we
clearly see why the embryos of mammals, birds, reptiles, and fishes
so closely
and
so unlike
adult forms. We may cease marvelling at the embryo of an air-breathing
or bird having branchial slits and arteries running in loops, like those
a fish which has to breathe
air dissolved in
by the aid of well-developed branchiæ. |
|
| Disuse, aided sometimes by natural selection,
often
→reduced
when
→they have become useless under
changed habits or
conditions of life; and we can
understand on this view the meaning of rudimentary organs. But disuse and selection will generally act on each creature, when it has come to maturity and has to play its full part in the struggle for existence, and will thus have little power
on an organ during early life; hence the organ will
|
