177. ANTHOZOA. 



255 



and have assumed a plan of four or ten, but without altering the primitive 

 conditions. 



In the Octocoralla (fig. 204) the conditions 

 are simpler, only eight septa being developed. 

 These are disposed equally on either side of the 

 oesophagus and may have (most octocorallans) 

 all their muscles towards one end, or (Edwardsia, 

 fig. 205, IV) may have the muscles of one pair 

 reversed. It is to be noted that hexactinians 

 pass through an Edwardsia stage. In Cerianthus 

 new septa are always added at one end of the sag- 

 ittal axis (fig 205, II), while in the extinct Tetra- 

 coralla (fig. 205, I), so far as one may judge from 

 the hard parts, the septa have an arrangement 

 with four as the basis. 



FIG. 204. Transverse sec- 

 tion of an Octocprallan 

 (Alcyonium). x, siphono- 

 glyphe; 1-4, septa of one 

 side, wi 



with their muscles 

 on one side, symmetrical 

 with those of the other 

 side. 



IV 



FIG. 205. Arrangement of septa in various Actinozoa. I, Tetracoralla ; II, Cerian- 

 thus; III, Octocoralla; IV, Edwardsia. 



By far the greater part of the Anthozoa reproduce by budding 

 as well as by eggs. Only rarely do the buds separate, but generally 

 they remain connected with the mother to form a colony of hun- 

 dreds or thousands of individuals. These are connected by an 

 extensive coenenchym or coenosarc, consisting largely of mesoglcea, 

 but having an outer coat of ectoderm and penetrated by a system 

 of branching and anastomosing entodermal canals (fig. 206). On 

 disturbance the polyps can quickly retract themselves into the 

 coenosarc. 



The colonial Anthozoa have almost invariably a skeleton, 

 secreted by the ectoderm and consisting either of calcic carbonate 

 or of an organic horn-like substance. Sometimes the horn and 

 lime alternate. One recognizes an axial and a cortical substance. 

 The axial skeleton is confined to the deeper portions of the coenosarc, 

 while the cortical portions are formed by the polyps themselves 

 and to a large extent (figs. 207, 208) repeat their complicated 

 structure. Except in a few forms (Fungia) a theca is present ; 

 this is a calcareous cup, and from this usually extend inward 

 calcareous partitions called, in distinction to the fleshy- or sarco- 

 septa, the sclerosepta. 



