CAMBRIAN INVERTEBRATES 



119 



1859^ as to the great duration that must be assigned to pre- 

 Cambrian time to allow for the evolution of highly specialized 

 life forms. 



By Middle Cambrian time the adaptive radiation of the 

 Invertebrata to all the conditions of life — ^in continental waters, 



PALEOGEOGRAPHY. LATE LOWER CAMBRIAN (WAUCOBIAN OR OLENELLUS) TIME 

 AFTER SCHUCHERT, APRIL, 1916 

 ^^MARINE DEPOSITS «»" ACTIVE VOLCANOES IM SCOTLAND *-" MOUNTAINS A ■ ARCMAEOCYATHINAE 



Fig. 19. Theoretic World Environment in Late Lower Cambrian Time. 



This period corresponds with that of the first well-known marine fauna with trilobites 

 and brachiopods as the dominant forms. No land life of any kind is known, and the 

 climate appears to have been warm and equable the world over. After Schuchert. 



along the shore-lines, and in the littoral and pelagic environ- 

 ment of the seas — appears to have been governed by mechan- 

 ical and chemical principles fundamentally similar to those 

 observed among the Protozoa, but distributed through myriads 

 of cells and highly complicated tissues and organs, instead of 

 being differentiated within a single cell as in the ciliate Pro- 

 tozoa. Among the elaborate functions thus evolved, showing 



■ Darwin. Charles, 1850, pp. 306, 307. 



