| → thickened stems 1859 1860 1861 1866 1869 |
| strikingly similar shape 1872 |
|
| → common and 1859 1860 1861 1866 1869 |
| body in the improved breeds of the Chinese and common pig, which are descended from distinct species; and in the similarly thickened stems of the common and specifically distinct 1872 |
|
| → widely distinct animals. 1869 |
| very distinct animals. 1859 1860 1861 1866 |
|
widely different animals.
1872 |
|
| → class or one order 1866 1869 |
| class or order 1859 1860 1861 |
| group 1872 |
|
| → class or order 1859 1860 1861 1866 1869 |
| group 1872 |
|
| → together: 1866 1869 1872 |
| one with another: 1859 1860 1861 |
|
| → the shape 1859 1860 1861 1866 1869 |
| between the several members 1872 |
|
| → body and 1859 1860 1861 1866 1869 |
| whale family, the shape of the body and the 1872 |
|
| → between the several members of 1859 1860 1861 1866 1869 |
| for as these parts are so nearly similar throughout 1872 |
|
| → for these cetaceans agree in so many characters, great and small, that 1859 1860 1861 1866 1869 |
| OMIT 1872 |
|
| → inherited their general shape of body and structure of limbs 1859 1860 1861 1866 1869 |
| been inherited 1872 |
|
| ↑ 15 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| Numerous cases could be given of striking resemblances in quite distinct beings between single parts or organs, which have been adapted for the same functions.
A good instance is afforded by the close resemblance of the jaws of the dog and Tasmanian wolf or Thylacinus,— animals which are widely sundered in the natural system. But this resemblance is confined to general appearance, as in the prominence of the canines, and in the cutting shape of the molar teeth.
For the teeth really differ much: thus the dog has on each side of the upper jaw four pre-molars and only two molars; whilst the Thylacinus has three pre-molars and four molars.
The molars also differ much in the two animals in relative size and structure.
The adult dentition is preceded by a widely different milk dentition.
Any one may of course deny that the teeth in either case have been adapted for tearing flesh, through the natural selection of successive variations; but if this be admitted in the one case, it is unintelligible to me that it should be denied in the other.
I am glad to find that so high an authority as Professor Flower has come to this same conclusion.
The extraordinary cases given in a former chapter, of widely different fishes possessing electric organs,— of widely different insects possessing luminous organs,— and of orchids and asclepiads having pollen-masses with viscid discs, come under this same head of analogical resemblances.
But these cases are so wonderful that they were introduced as difficulties or objections to our theory.
In all such cases some fundamental difference in the growth or development of the parts, and generally in their matured structure, can be detected. The end gained is the same, but the means, though appearing superficially to be the same, are essentially different.
The principle formerly alluded to under the term of
analogical
variation
has probably in these cases often come into play that is, the members of the same class, although only distantly allied, have inherited so much in common in their constitution, that they are apt to vary under similar exciting causes in a similar manner; and this would obviously aid in the acquirement through natural selection of parts or organs, strikingly like each other, independently of their direct inheritance from a common progenitor.
As species belonging to distinct classes have often been adapted by successive slight modifications to live under nearly similar circumstances,— to inhabit, for instance, the three elements of land, air, and water,— we can perhaps understand how it is that a numerical parallelism has sometimes been observed between the sub-groups of distinct classes.
A naturalist, struck with a parallelism of this nature, by arbitrarily raising or sinking the value of the groups in several classes (and all our experience shows that their valuation is as yet arbitrary), could easily extend the parallelism over a wide range; and thus the septenary, quinary, quaternary and ternary classifications have probably arisen.
There is another and curious class of cases in which close external resemblance does not depend on adaptation to similar habits of life, but has been gained for the sake of protection.
I allude to the wonderful manner in which certain butterflies imitate, as first described by Mr. Bates, other and quite distinct species.
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