ACTINOZOA. 155 



pears as a soft, fleshy covering, from which the 

 several polypes arise, their somatic cavities freely 

 communicating one with another. 



Far different in its nature is the sclerodermic 

 corallum, deposited, as above stated, within the 

 bodies of polypes, which, in some cases, remain 

 separate, but, in others, multiply by continuous 

 gemmation. And, just as the whole body of an 

 Actinozoon is made up either of one polype or of 

 several united by a coenosarc, so, too, may the 

 fully developed sclerodermic corallum consist of 

 a single ' corallite ' or of several connected by a 

 ' coenench}TTia '. 



The parts of a typical corallite are these {fig, 

 28). First, an outer wall, or 'theca', somewhat 

 cylindrical in form, terminating distally in a 

 cup-like excavation, or ^ calice ', and having its 

 central axis traversed by a ^ columella '. The 

 space between this and the theca is divided into 

 * loculi ', or chambers, by a number of radiating 

 vertical partitions, the ' septa '. These do not, in 

 certain instances, quite reach the columella, but 

 are broken up into upright pillars, or ' pali ', 

 arranged in one, two, or three circular rows, 

 termed ' coronets '. All the preceding parts are 

 best brought into view by transverse section. 

 Longitudinal division of a corallite shows, fre- 

 quently, the existence of imperfect transverse 

 partitions, or ^dissepiments', which, growing from 

 the sides of the septa, interfere, to a greater or 

 less extent, with the perfect continuity of the 

 loculi. Sometimes the septa have their "sides 

 covered with styliform or echinulate processes, 

 which, in general, meet so as to constitute nume- 

 rous ' synapticulse ', or transverse props, extending 



