ACTINOZOA. 161 



by the perfect scl-erodermic corallum. Its decalcifi- 

 cation, liowever, reveals delicate shreds of the 

 periplastic substance by which it had been de- 

 posited, usually exhibiting an irregular reticulating 

 arrangement. The * sclerenchyma/ or coral tissue, 

 presents every gradation between this nearly solid 

 condition and the spicular stage permanently ex- 

 emplified in Ah'i/onium. Thus, in the Aporosa, 

 it is iirm and compact; in the Perforata, porous 

 and granular, or even spongy and reticulate. 



In the accompanpng table the chief modifica- 

 tions of the corallum, from an artificial point of 

 ■y;iew, 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 

 GorcjonidcB 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 sjDicules will 

 be found gently adhering to the brown, horny 

 sclerobasis below. i\i. Valenciennes has proposed 

 to distinguish five kinds of these spicules, or 

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

 massive, stellate, and squamous, respectively. 



KEY TO MODIFICATIONS OF COEALLUM. 



Corallum wholly sclerodermic. 

 Corallum thecal, calcareous. 

 Tabulae present. 



Septa in X of 4 Eugosa. 



Septa in x of 5 or 6, rudimentary or 



absent Tabulata. 



Tabulae absent. 



Septa weU marked, in x of 5 or 6. 



SclerenchjTna porous. . . . Perforata. 

 M 



