| → manner two parts in two organic beings, which beings owe but little of their structure in common to inheritance from the same ancestor. 1860 1861 |
| manner two parts in two organic beings, which owe but little of their structure in common to inheritance from the same ancestor. 1859 |
| yet some fundamental difference between them can always, or almost always, be detected. 1866 1869 |
| yet fundamental differences between them can always be detected. 1872 |
|
| ↑ 10 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| For instance, the eyes of cephalopods or cuttle-fish and of vertebrate animals appear wonderfully alike; and in such widely sundered groups no part of this resemblance can be due to inheritance from a common progenitor.
Mr. Mivart has advanced this case as one of special difficulty, but I am unable to see the force of his argument.
An organ for vision must be formed of transparent tissue, and must include some sort of lens for throwing an image at the back of a darkened chamber.
Beyond this superficial resemblance, there is hardly any real similarity between the eyes of cuttle-fish and vertebrates, as may be seen by consulting Hensen's admirable memoir on these organs in the Cephalopoda.
It is impossible for me here to enter on details, but I may specify a few of the points of difference.
The crystalline lens in the higher cuttle-fish consists of two parts, placed one behind the other like two lenses, both having a very different structure and disposition to what occurs in the vertebrata.
The retina is wholly different, with an actual inversion of the elemental parts, and with a large nervous ganglion included within the membranes of the eye.
The relations of the muscles are as different as it is possible to conceive, and so in other points.
Hence it is not a little difficult to decide how far even the same terms ought to be employed in describing the eyes of the Cephalopoda and Vertebrata.
It is, of course, open to any one to deny that the eye in either case could have been developed through the natural selection of successive, slight variations; but if this be admitted in the one case, it is clearly possible in the other; and fundamental differences of structure in the visual organs of two groups might have been anticipated, in accordance with this view of their manner of formation.
|
|
| ↑ 1 blocks not present in 1859 1860 1861; present in 1872 1866 1869 |
| I am inclined to believe that in nearly
the same way as two men have sometimes independently hit on the very same
invention, so natural
selection, working for the good of each being
and taking advantage of analogous
variations, has sometimes modified in very nearly the same manner two parts in two
organic
beings, which owe but little
of their structure in common to inheritance from the same ancestor.
|
|
| → Although 1859 1860 1861 |
| Finally then, although 1866 1869 1872 |
|
| → to the extinct and unknown 1859 1860 1861 |
| is to the extinct and unknown, 1869 1872 |
| OMIT 1866 |
|
| → is very small, 1859 1860 1861 |
| is very small 1866 |
| OMIT 1869 1872 |
|
| → I 1859 1860 1861 1869 1872 |
| compared with the extinct and unknown forms, I 1866 |
|
| → The truth of this remark is indeed 1859 1860 |
| It certainly is not true, that new organs often appear suddenly in any class, as if created for some special purpose; as indeed is 1861 |
| It certainly is true, that new organs very rarely or never suddenly appear in any class, as if created for some special purpose; as indeed is 1866 |
| It certainly is true, that new organs appearing as if specially created for some purpose, rarely or never appear suddenly in any class; as indeed is 1869 |
| It certainly is true, that new organs appearing as if created for some special purpose, rarely or never appear in any being;— as indeed is 1872 |
|
| → but somewhat exaggerated canon 1860 |
| canon 1859 |
| but somewhat exaggerated, canon 1861 1866 1869 1872 |
|
| → so? 1859 1860 1861 |
| so much variety and so little novelty? 1866 1869 |
| so much variety and so little real novelty? 1872 |
|
| → leap, 1859 1860 1861 |
| sudden leap, 1866 1869 |
| great and sudden leap, 1872 |
|
| → the shortest and slowest 1859 1860 |
| short and slow 1861 |
| short and sure though slow 1866 1869 |
| short and sure, though slow 1872 |
|
| →
importance
.—
1859 1860 1861 |
|
Importance, as affected by Natural Selection. 1866 |
|
Importance, as affected by Natural Selection. 1869 |
|
Importance, as affected by Natural Selection
. 1872 |
|
| → individuals with any favourable variation, 1859 1860 1861 1866 |
| the fittest, 1869 1872 |
|
| → those with any unfavourable deviation of structure,— I have sometimes felt much difficulty in understanding the origin of simple parts, of which the importance does not seem sufficient to cause the preservation of successively varying individuals. 1859 1860 1861 |
| those with any unfavourable deviation of structure,—I have sometimes felt much difficulty in understanding the origin of simple parts, of which the importance does not seem sufficient to cause the preservation of successively varying individuals. 1866 |
| the less well fitted individuals,—I have sometimes felt great difficulty in understanding the origin or formation of parts of little importance; almost as great, though of a very different kind, as in the case of the most perfect and complex organs. 1869 |
| the less well-fitted individuals, 1872 |
|
