ACTINOZOA. 



161 







by the perfect sclerodermic corallum. Its decalcifi- 

 cation, however, reveals delicate shreds of the 

 periplastic substance by which it had been de- 

 posited, usually exhibiting an irregular reticulatin 

 arrangement. The ' sclerenchyma/ or coral tissue, 

 presents every gradation between this nearly solid 

 condition and the spicular stage permanently ex- 

 emplified in Alcyonium. Thus, in the Aporosa, 

 it is firm and compact; in the Perforata, porous 

 and granular, or even spongy and reticulate. 



In the accompanying table the chief modifica- 

 tions of the corallum, from an artificial point of 

 view, are systematically exhibited. 



It must not, however, be supposed that the 

 presence of a sclerobasis renders the deposition of 

 tissue secretions wholly impossible, for, among the 

 Gorgonidce it is certain that, in addition to the 

 basal corallum, true sclerodermic spicules appear, 

 within the substance of the investing mass. When 

 such a Gorgonia is dried, and the soft parts washed 

 away, a thin layer of calcareous spicules will 

 be found gently adhering to the brown, horny 

 sclerobasis below. M. Valenciennes has proposed 



kinds of these spicules, or 

 'sclerites, 5 by the names of capitate, fusiform, 

 massive, stellate, and squamous, respectively. 



KEY TO MODIFICATIONS OF CORALLUM. 



Corallum wholly sclerodermic. 

 Corallum thecal, calcareous. 

 Tabulse present. 



Septa in x of 4 Eugosa. 



• Septa in x of 5 or 6, rudimentary or 



absent. . ... . . . Tabulata. 



to distinguish five 



Tabulae absent. 

 Septa well marked, in x of 5 or 6. 



Sclerenchyma porous. 



Perforata. 



M 



