| → however slight, in its development, 1859 1860 1861 1866 1869 |
| OMIT 1872 |
|
| → seized on by natural selection, 1859 1860 1861 1866 1869 |
| favoured, 1872 |
|
| → by the parasitic habits 1859 1860 1861 1866 1869 |
| would be a decided advantage to each successive individual 1872 |
|
| → Proteolepas, though effected by slow steps, would be a decided advantage to each successive individual of the 1859 1860 1861 1866 1869 |
| OMIT 1872 |
|
| → in reducing and saving every 1859 1860 1861 1866 1869 |
| to reduce any 1872 |
|
| → is rendered 1859 1860 1861 1866 1869 |
| becomes, through changed habits, 1872 |
|
| → superfluous, 1859 1860 1861 1872 |
| by changed habits of life superfluous, 1866 1869 |
|
|
changed conditions of life a
before
becomes less useful,
→however slight, in its development,
will be
→seized on by natural selection,
for it will profit the individual not to have its nutriment wasted in building up an useless structure. I can thus only understand a fact with which I was much struck when examining cirripedes, and of which many
instances could be given: namely, that when a cirripede is parasitic within another
is thus protected, it loses more or less completely
own shell or carapace. This is the case with the male Ibla, and in a truly extraordinary manner with the Proteolepas: for the carapace in all other cirripedes consists of the three highly-important anterior segments of the head enormously developed, and furnished with great nerves and muscles; but in the parasitic and protected Proteolepas, the whole anterior part of the head is reduced to the merest rudiment attached to the bases of the prehensile antennæ. Now the saving of a large and complex structure, when rendered
→by the parasitic habits
of the
→Proteolepas, though effected by slow steps, would be a decided advantage to each successive individual of the
species; for in the struggle for life to which every animal is exposed, each
would have a better chance of supporting itself, by less nutriment being
|
|
| Thus, as I believe, natural selection will
in the long run
→in reducing and saving every
part of the organisation, as soon as it
→is rendered
→superfluous,
without by any means causing some other part to be largely developed in a corresponding degree. And, conversely, that natural selection may perfectly well succeed in largely developing
without requiring as a necessary compensation the reduction of some adjoining part.
|
