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 euryp- 

 terids. 



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 orig- 

 inally independent segments. According to what may be 

 called the orthodox view, all the resemblances between verte- 

 brates 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 verte- 

 brates known. 



The Earliest Ch or dates 



Recently Professor Johan Kiaer has described many beauti- 

 fully 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 Stensio has collected 



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