58 THE CHAIN OF LIFE. 



modern star coral, represented in Fig. 42, is an instance of the 

 latter condition. It shows nineteen or twenty animals, each 

 with a central mouth and fringe of short tentacles, aggregated 

 together, and two of them showing the spontaneous division by 

 which the number of animals in the mass is progressively 

 increased. The living coral shows only the soft animals and 

 the animal matter connecting them ; but if dead there would 

 be a white stony mass with a star-like cell or depression 

 cor'-esponding to each animal. 



; ii their general plan, the oldest Corals were precisely of this 

 character, but they presented some differences in detail, which 

 have caused them to be divided into two groups, which are 

 eminently characteristic of the Palaeozoic age — the tabulate 



' j"^.. 





:*La.i 





Fig. 42. — Living Anthozoan Coral (Asireen). 



or floored corals, and the rugose or wrinkled corals. In the 

 former (Fig. 43) the cells are usually small and thin-walled, 

 often hexagonal, like a honeycomb, and are floored across at 

 intervals with tabulae or horizontal plates. A few modern 

 corals present a similar arrangement,^ but this kind of structure 

 was far more prevalent in the Palaeozoic. In the second type 

 the animals are usually larger and often solitary, the cell has 

 strongly marked radiating plates, while the horizontal floors 

 are absent or subordinate, and there is usually a thick exter- 

 nal rind or outer coat (Figs. 44, 45). In general plan, these 



^ Heliopora^ an Alcyonarian ; PocUhpora, an Anthozoan, 



'ill 



