THE LINEAGE OF MAN
single cell or pole cell. Professor William Patten, on the contrary, holds that this distinction is not a fundamental one and that the vertebrates have been derived from some early member of the arthropod series, such as the fossil eurypterids.
Both the vertebrates and the arthropods are many-jointed animals provided with an elaborate locomotor apparatus, and both have a highly complex head, which has apparently developed through the growing together of a number of originally independent segments. According to what may be called the orthodox view, all the resemblances between vertebrates and arthropods have been independently acquired in these two great groups, for both had to solve many similar mechanical problems in the perception, pursuit, ingestion, and digestion of their food. According to Professor Patten, on the other hand, the arthropod mechanisms were attained first and afterward were changed to form the vertebrate ground-plan of organization along lines which he has inferred, but which the orthodox reject as requiring too many hypothetical stages between arthropods and the oldest vertebrates known.
The Earliest Chordates
Recently Professor Johan Kiaer has described many beautifully preserved fossil fish-like forms from the Silurian rocks of Norway. These fossils belong to a group of animals, hitherto known chiefly from the Silurian and Devonian rocks of Scotland and Russia, which are commonly called ostracoderms. Some (including Cephalaspis) were flat-bodied like skates; others were shaped more like ordinary fishes. The modern lampreys appear to be degenerate descendants of this group, which is also remotely related to the sharks and higher fishes. Professor Stensiö has collected
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