CORALS AND CORAL MAA'ERS. 



from the Mediterranean, the upper extremity is a depression, 

 or caliclc, inclosed by a series of radiating calcareous (coral) 

 septa. Each of these septa is secreted between a pair of the 

 radiating fleshy partitions, or septa, of the polyp (see figure ]). 

 lo); and thus the radiate structure of ordinary corals is 

 nothing but an expression of the internally. radiate structure ot 

 the polyp. When aUve, the top, and usually the sides, of the 

 coral were concealed by the outer skin of the polyp, including, 

 above, the disk and tentacles ; and into the depression or 

 calicle at top, descended the stomach. 



Whether these radiating septa of 

 the coral are secreted from the sur- 

 faces of the fleshy septa, or trom a 

 ]jrolongation inward of the mem- 

 brane forming the walls of the inter- 

 nal cavity, has not been directl}' ascer- 

 tained. The latter view is sustained 

 by Professor Verrill, on the ground 

 that the coral septa contain fibres 

 of animal tissue. The secretion does 

 not always commence at the central 

 plane of a septum, for the septa are 

 sometimes hollow within, just as the surface spines of some 



■HEC0CVATHL:S CVLINDKACCrS. 



FLABELLL'M I'AVONINUM. 



species (e.g., Echinopora irjfcxa) are hollow. The exterior 

 surface of the corallum, that is, the part outside of the calicles, 



