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 Actinia. 
But a new feature is added to the complication 
of their structure, as compared with Actiniz, 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 Astreeans, the multiplication of tenta- 
eles is more definite and limited, rising some- 
times to ninety and more, though often limited to 
forty-eight in number, and the transvers floors 
between the vertical partitions are more com- 
plete than in the Fungids. The Porites have 
twelve tentacles only, never more and never les, 
