I 



^ 



THE AGE OF INVERTEBRATES OF THE SEA. $7 



like that represented in Fig. 39^, are very characteristic of the 

 Carboniferous. These animals, individually small, though com- 

 plicated in structure and branching into communities, scarcely 

 ever of any great magnitude, humble creatures which have 

 never played any great part in the world, have, nevertheless, 

 been so persistent that, though specific and generic forms have 

 been changed, the group may be said to be in the modern seas 

 exactly what it was in those of the early Palaeozoic, nor can it 

 be affirmed to have originated in anything different, or to have 

 produced anything. 



The true Stony Corals (A n//iozoa) are as yet unknown in the 



Fig. 41.— a, Stetiopora exi/is (Dawson), b, Chaetetes Unnidiisi^Awz.tA% and Haine). 



Carboniferous. 



Cambrian. They entered on the stage in immense abundance 

 in the Siluro -Cambrian, where considerable limestones are 

 largely composed of their remains, mixed, however, and some- 

 times overpowered with those of Bryozoa and Hydroids. An 

 ordinary coral, such as those of which coral reefs are built — 

 the red coral used for ornament is not quite similar — is the 

 skeleton of an animal constructed on the plan of a sea anemone ; 

 with a central stomach surrounded by radiating chambers, and 

 having above a crown of tentacles. The stony coral sur- 

 rounds and protects the soft body of the animal, and may 

 either be a single cell, for one animal, or an aggregation of 

 such cells, constituting; a rounded or branching mass. The 



