ZOANTHARIA. 



181 



known as the " visceral chamber," is variously subdivided 

 below, and superiorly presents itself as a shallower or 

 deeper cup-shaped depression, termed the " calice." Within 

 the calice is contained, in the living state, the stomach-sac of 

 the polype ; and the visceral chamber below the calice is sub- 

 divided into a number of vertical compartments the " in- 

 terseptal loculi "this subdivision being effected by means 

 of calcareous partitions or " septa," which spring from the 

 inner wall of the theca, and are directed inwards towards 

 the centre. The " septa " correspond with the " mesenteries " 

 of the living animal, with which they agree in number and 

 size. Some of them the so-called " primary septa " are 

 much wider than the others, and may extend far enough 

 inwards to meet in the centre of the visceral chamber (fig. 

 70, A). Others of the septa fall short of the centre by a 



Fig. 70. Diagram of the arrangement of the septa in the Zoantharia sclerodennata and 

 Rngosa. A, Transverse section of a simple sclerodermic coral (Turbinolia), showing the theca, 

 with its projecting ridges or "costse" outside, the visceral chamber and radiating septa 

 inside, and the columella in the centre ; B, Transverse section of a simple Rugose coral (Cyatho- 

 phyllum), showing the wall, costae, and septa. 



greater or less distance, and are known as the " secondary " 

 and " tertiary " septa, according to their width. In the centre 

 of the visceral chamber there may or may not be an axial 

 calcareous rod, known as the "columella" (fig. 70, A). The 

 structure of the columella varies in different cases, but it 

 extends, typically, from the floor of the visceral chamber to 

 the bottom of the calice, into which it projects for a greater 

 or less distance, and the primary septa are often closely con- 

 nected with it. 



