. The doctrine of descent and Darwinism. Evolution. GRAPTOLITES—TRILOBITES. fusion of life met with in the Silurian and Devonian strata presupposes an immeasurably long antecedent period during which life had already existed and gradu- ally increased to the multitudes of the Silurian era. We discover in it but scanty remains of marine plants, and only marine animals; but these are so heterogeneous and varied in form, that they alone would oblige us to infer the existence of coasts, shallow or deep oceanic regions, and a number of geographical conditions on which we see the variety and extent o
. The doctrine of descent and Darwinism. Evolution. GRAPTOLITES—TRILOBITES. fusion of life met with in the Silurian and Devonian strata presupposes an immeasurably long antecedent period during which life had already existed and gradu- ally increased to the multitudes of the Silurian era. We discover in it but scanty remains of marine plants, and only marine animals; but these are so heterogeneous and varied in form, that they alone would oblige us to infer the existence of coasts, shallow or deep oceanic regions, and a number of geographical conditions on which we see the variety and extent of animal life to be dependent. Besides numerous forms of corals more nearly allied to still exist- ing families, we find the quite peculiar group of Graptolites (fig. 9), which, although not actual polypes, might be ranged next to the so-called Medusa- polypes, and thus justify the inference that preparation was being made for the appearance of the higher forms of the Coelenterata, the Medusae. The Articulata are represented by the Trilobites (fig. lO, Trilobites remipes), a crab-like form which recalls the pre- sent group of the Lamellibranchiata, but has not hitherto admitted of any closer definition, as in none of the many thousand specimens examined, of the forms (about 2000) known in the Silurian and Devonian strata, have the legs been preserved. In these three-lobed crabs, the head, trunk, and tail distinctly ap- pear, as well as the threefold transverse division. The two composite eyes already indicate a high grade of organization. The power of rolling themselves up,. FfG. 9-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Schmidt, Dr. (Eduard Oskar), 1823-1886. London, H. S. King & Co.
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