The doctrine of descent and Darwinism / by Oscar Schmidt.

  • Schmidt, Oscar, 1823-1886
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: The doctrine of descent and Darwinism / by Oscar Schmidt. Source: Wellcome Collection.

    87/401 (page 71)
    circumstance, certainly very important, that of the Cephalopoda the Nautilus alone is found. The Brachio- poda soon attain to their highest development, and have lingered on till now in a greatly reduced state. Among the Conchifera, the Dimyariae take the lead in the course of the later period; and with regard to the Gasteropods, we will merely observe that they constantly increase in internal complexity and variety as they approach more recent periods, and that the terrestrial and fresh-water species are occasionally found in the carboniferous formation, though in number and variety they belong primarily to the Tertiary era. To the Cephalopoda we must return again. Of the Vertebrata in the Silurian strata we know only the remains of peculiar Fishes whose kindred must be sought among the sharks and rays. In the period of the Devonian or upper Transition rocks, the surface of the earth had assumed, at least in places, a more smiling appearance. Here begins the first record of terrestrial plants. As to the character of the fauna, the rapid decrease of the Trilobites is worthy of notice, and the appearance of the important genus of the Cephalopoda, Clymenia, subsequently replaced by the Ammonites. . Above all, we must note the increased abundance of fish which still form the sole representatives of the Vertebrata, and held undisputed sway in the seas of that period. Besides the sharks, there are the mailed Ganoids. It is true, the fish, the hinder part of which is here portrayed (Fig. 11, Palaeoniscus), belongs only to the upper Coal and Zechstein formation ; but it is necessary even now to point out the character- istics of the true Ganoids which floundered about the Silurian seas in somewhat extraordinary forms. Agassiz