| → leg 1859 1860 1861 1866 |
| in the leg 1869 1872 |
|
| → intelligible 1859 1860 1861 1866 1869 |
| to a large extent, intelligible 1872 |
|
| → alike in the 1859 1860 1861 1866 |
| aboriginally alike in an 1869 1872 |
|
| → class. 1859 1860 1861 1866 |
| of these classes. 1869 1872 |
|
| → tend to reduce an 1859 1860 1861 1866 |
| reduced 1869 |
| have reduced 1872 |
|
| → it has become useless by 1859 1860 1861 1866 |
| they have become useless under 1869 |
| rendered useless under 1872 |
|
| → reduced, during successive genera- tions, 1861 |
| reduced, during successive generations, 1859 1860 1866 1869 |
| formerly reduced 1872 |
|
|
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
→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
→alike in the
early progenitor
each
→class. 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
→tend to reduce an
when
→it has become useless by
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 not be
reduced or rendered rudimentary at this early age. The calf, for instance, has inherited teeth, which never cut through the gums of the upper jaw, from an early progenitor having well-developed teeth; and we may believe, that the teeth in the mature animal were
→reduced, during successive genera- tions,
|
