| → the 1859 1860 1861 1866 1869 |
| one of the 1872 |
|
| ↑ 4 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| How curious it is, to give a subordinate though striking instance, that the hind-feet of the kangaroo, which are so well fitted for bounding over the open plains,— those of the climbing, leaf-eating koala, equally well fitted for grasping the branches of trees,— those of the ground-dwelling, insect or root-eating, bandicoots,— and those of some other Australian marsupials,— should all be constructed on the same extraordinary type, namely with the bones of the second and third digits extremely slender and enveloped within the same skin, so that they appear like a single toe furnished with two claws.
Notwithstanding this similarity of pattern, it is obvious that the hind feet of these several animals are used for as widely different purposes as it is possible to conceive.
The case is rendered all the more striking by the American opossums, which follow nearly the same habits of life as some of their Australian relatives, having feet constructed on the ordinary plan.
Professor Flower, from whom these statements are taken, remarks in conclusion: "We may call this conformity to type, without getting much nearer to an explanation of the phenomenon;" and he then adds "but is it not powerfully suggestive of true relationship, of inheritance from a common ancestor?"
|
|
| → connexion 1859 1860 1861 1866 |
| position or connexion 1869 1872 |
|
|
This resemblance is often expressed by the term "unity of type;" or by saying that the several parts and organs in the different species of the class are homologous. The whole subject is included under the general
of Morphology. This is
→the
most interesting
of natural history, and may
said to be its very soul. What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include
bones, in the same relative positions? ↑
Geoffroy St. Hilaire has
on the high importance of relative
→connexion
in homologous
may
to almost any extent in form and size, and yet
remain connected together in the same
We never find, for instance, the bones of the arm and
or of the thigh and leg, transposed. Hence the same names can be given to the homologous bones in widely different animals. We see the same great law in the construction of the mouths of insects: what can be more different than the immensely long spiral proboscis of a sphinx-moth, the curious folded one of a bee or bug, and the great jaws of a beetle? — yet all these organs, serving for such
purposes, are formed by infinitely numerous modifications of an upper lip, mandibles, and two pairs of maxillæ.
the construction of the mouths and limbs of crustaceans. So it is with the flowers of plants. |
|
| Nothing can be more hopeless than to attempt to explain this similarity of pattern in members of the same class, by utility or by the doctrine of final causes. The hopelessness of the attempt has been expressly admitted by Owen in his most interesting work on the 'Nature of Limbs.' On the ordinary view of the
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