Chap. IX.] 



PARTS OF CORALS. 



283 



the common Fimgia, the spicules are found in the 

 septa only, while the body wall remains soft. 

 Finally, the axis common to a colony of polyps may 

 become calcined as well as the body wall and the 

 septa (Fig. 118 c), and we then get large masses 

 of hard stony-like structures which persist long after 

 the polyps that formed them are dead and decayed 

 (brain-coral). 



In describing the skeletons of corals use is made 

 of the following terms : the wall of 

 the cup-like calcification is called the 

 theca, and consists sometimes of 

 an exo- and endo- theca; where the 

 theca is thin it is aided by an in- 

 vesting epitlieca ; the space be- 

 tween the calcined septa are the 

 loculi; the septa may unite in the 

 centre to form a pseudo-coluan- 

 ella, or may be inserted into an 

 axial hard part of distinct origin, 

 which is the true columella; the 

 ridges or outgrowths on this are the 

 pali, and the synapticnlae are the 

 plates that project transversely and 

 connect one septum with another, 

 sometimes divided into chambers which rise one above 

 the other, like storeys, and the floor of each of these 

 is a tabula. The ridges on the exotheca are known 

 as costSB. 



The hard connecting sclerenchyma may be compact, 

 as in the stony corals, or traversed by canals, as in the 

 red coral (Fig. 117). 



Among the Hydrozoa continuous coralla are 

 found only in the Hydrocorallina?, where they are 

 formed by the ectoderm which covers the canals that 

 traverse and branch in the " ccenosarc," that is 

 common to the compound stock of polyps ; the 



Fig. 118 A. Coral. 

 Two tubes of 

 Tiibipora musica, 

 viiih. their con- 

 tained polyps. 



The loculi are 



