194 AGE OF CORAL REEFS. 



in the formation of Reefs. In these, also, the 

 tentacles multiply throughout life, though they 

 are usually not so numerous as in the Actiniae. 

 But a new feature is added to the complication 

 of their structure, as compared with Actiniae, in 

 the transverse beams which connect their vertical 

 partitions, though they do not stretch across the 

 chambers so as to form perfect floors, as in some 

 of the higher Polyps. These transverse beams or 

 floors must not be confounded with the horizon- 

 tal floors alluded to in a former article as char- 

 acteristic of the ancient Acalephian Corals, the 

 Rugosa and Tabulata. For in the latter these 

 floors stretch completely across the body, unin- 

 terrupted by vertical partitions, which, if they 

 exist at all, pass only from floor to floor, instead 

 of extending unbroken through the whole height 

 of the body, as in all Polyps. Where, on the 

 contrary, transverse floors exist in true Polyps, 

 they never cut the vertical partitions in their 

 length, but simply connect their walls, stretching 

 wholly or partially from wall to wall. 



In the Astraeans, the multiplication of tenta- 

 cles is more definite and limited, rising some- 

 times to ninety and more, though often limited to 

 forty-eight in number, and the transverse floors 

 between the vertical partitions are more com- 

 plete than in the Fungidas. The Porites have 

 twelve tentacles only, never more and never less, 



