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system; sometimes it grows on certain parts of the surface of that 

 membrane, and forms a kind of calciferous epidermis similar to 

 that which covers the skin of Mollusca and Crustacea. This 

 epidermic sderenchyma is the " foot secretion " of Dana, or 

 *^ sclerobassic corallum;" it forms the Red Coral, Gorallium, and 

 the stems of Jsts, and Mopsea,}ik.ewise the tubular horny sheaths of 

 8ertularia, Campanularia, and other Hydroid Zoophytes, and the 

 rooted, branched, plant-like stem of the sea shrubs or Gorgonidoe. 

 The dermic sderenchyma, or ossified chorion, is deposited within 

 the bodies of Polyps : the calcification of this tissue always 

 commences in the centre of the lower part of the Polyp, and 

 extending, gradually rises as the animal grows, so as to enclose 

 the lower part of the gastric cavity, and to constitute a sort of 

 cup or cell which is broad, or shallow, long, or tubular, 

 according to the destined condition of the Polypi ; in fact, the 

 " sclerodermic coraUum" may be likened to the body walls of an 

 Actinia, hardened by the deposition of inorganic matter therein, 

 and thus petrifying aU the deKcate structures of its walls, base, 

 and septa, by an interstitial deposit of calcareous salts, forming, 

 so to speak, a mould of the organism : and as the whole body 

 of an actinozoon may be made up either of one Polype, or of 

 several united together by a ccenosarc, so may the fully 

 developed sclerodermic corallum consist of a single CoraUite, or 

 of several connected by a ccenenchyma. 



The corallum, or skeleton, is simple, when it belongs to a single 

 isolated individual, and compound, when it results from the 

 union of many bound together by a ccenenchyma or connecting 

 calcareous tissue. The following definition of the terminology 

 employed in the description of Corals will assist the student to 

 understand the diagnosis of the different groups. 



The parts of a typical CoraUite, or simple Polyp skeleton, are 

 the following. First, an outer wall or theca, somewhat cylindrical 

 in form, terminating distally in a cup-Kke excavation or chalice, 

 and having its central axis traversed by a stem or columella. 

 The space between this and the theca is divided into loculi or 

 chambers, by a number of radiating vertical partitions or septa, 

 which do not always reach the columella, but are broken up 



