330 TBE SCIENTIFIC MONTHLY
other true Crustacea of the Cambrian, and to the ciiripedes or bar- nacles of the Ordovician.
Schucbert obBerves that there is no more significant period in the hiatorj of the world than the Devonian" (Fig, 13) for at this time the increasing verdure of the land invited the invasion of life from the waters, the first conquest of the terrestrial environment being attained
��Pio. 14. A. BE8TWRATION oi' Sfflloiiuni* exceUior, CatskiU, S*SMTOSt Natural teogtb, four ffet. B, R«alorBllaD of Buiarciu, Berttv wst«rUm«. Natural leOfftb, three feet. C. RestorntloD of tli« tillurliiD eurjpterld EuMarcia, *gt ot the Bertie waterllme. After Jotin M. Clarke,
by the scorpions, shell lish, worms and insects. This is an instance of the constant dispersion of animal forms into new environments for their food supply, the chief instinctive cause of all migration. This impulse is constantly acting and reacting throughout geologic time with the migration of the environment, graphically presented by Hunt- ington's chart from the researches of Barrell, Schucbert, and othera (Fig. 13, Huntington's chart). The periodic readjustment of the >4 Pirason, Louis V., and Sobuchert, Charles, 1915, p. 714.
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