Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/187

Rh organs, the abnormal in one animal being normal in another. Occasionally we find animals so badly organized as to make it incredible that they should have appeared on the earth as such originally. In speaking of the Sloth, Cuvier observes, "One finds them so little related to ordinary animals, the general laws of living organizations apply so little to them, the different parts of their body seem to be so much in contradiction with the rules of co-existence that we find established in the whole animal kingdom, that one could really believe that they are the remains of another order of things." Cuvier then continues by saying that in most forms the disadvantages are compensated by advantages, "but in the Sloth each singularity of organization seems to result only in feebleness and imperfection, and the inconveniences belonging to the animal are not compensated by any advantage."

The only explanation, at present, of the existence of such a wretched animal as the Sloth is that it is the degenerated representative of some extinct animal who lived at the same time as the Megatherium, which it resembles in the form of its head. The limbs and backbone of the Megatherium are, however, represented by the Great Ant-eater. The Sloths and Great Ant-eater are confined to South America, and it is there that the Megatherium remains have been found in great abundance.

The development of the flower through the gradual metamorphosis of the leaf is a beautiful illustration of the evolution of different forms from a common type. In the words of Prof. Gray, "The leaves of the stem, the leaves or petals of the flower, and even the stamens and pistils, are all forms of a common type, only differing in their special development; and it may be added that, in an early stage of development, they all appear nearly alike.