CCELENTERATA. 



by budding or cleavage from a primitive corallite, having their 

 outer walls closely amalgamated, but not sunk in any general 

 coenenchyma. In other cases, the ccenenchyma, though not 

 actually absent, is very much reduced in quantity. 



Fig. \\.'Michelinia convexa (D'Orbigny). A compound sclerodermic Coral. 



Devonian. 



To comprehend the more intimate structure of a sclero- 

 dermic coral, we may take a single 

 " corallite" of a composite form or, 

 better, the simple corallum secreted by 

 a form which never repeats itself by 

 gemmation or cleavage (fig. 42). Such 

 a coral consists of an outer wall, which 

 encloses an internal space or chamber, 

 and which assumes very various forms. 

 We may, however, take the simplest 

 and commonest form, in which the coral 

 is conical or turbinate in shape (fig. 42). 

 The outer wall of this cone is called the 

 " theca," and it encloses a space which 

 is variously subdivided below, but which 

 has the form of a shallower or deeper 

 conical cup towards its summit. This 

 vacant space is called the " calice," and 

 in the living state it contains the sto- 

 machal sac of the polype. The space below the calice is 

 broken up into a number of vertical compartments or "loculi," 



Fig. 42. Cyathaxonia, 

 Dalmani. A simple sclero- 

 dermic coral, showing the 

 theca, with its costae, the 

 calice, with the columella 

 in its centre, and the septa. 

 A portion of wall of the 

 theca is broken, in order 

 to show the interior of the 

 calice. 



