200 



ACTINOZOA. 



tentacles are capable of being extended to three 



{fig 



Hete- 



metis moniliform, in Corynactis and Caryophyl- 

 lia they terminate in globose heads. Their free 

 extremities are often perforate, the animal having 

 the power of opening or closing the orifice at 

 pleasure. _ Dana describes the inner tentacles of 

 his Actinia flagellifera as terminating in a re- 

 tractile pencil of hairs, but it is possible that these 

 hairs may have been, in reality, large everted 

 thread-cells. Although in most Zoantharia the 

 tentacles are simple, yet in Thalassianthus and 

 its allies they are branched, and have their surface 

 studded with tubercles or papillae. In a few 

 genera, two kinds of tentacles appear on the same 

 polype; the one simple, the other lobed or 

 branched, as in Phyllactis. 



The number of the tentacles, though in general 

 some multiple of five or six, is, in other respects, 

 liable to considerable variation. Their arrange- 

 ment, also, is correspondingly diversified. They 

 may dispose themselves in one, two, or more con- 

 centric series, and in some species they appear 

 irregularly scattered. Antipathes exhibits six 

 tentacles in a single circlet ; Peachia twelve, simi- 

 larly disposed ; while in the common Sea-anemone 

 there are nearly two hundred of these organs, 

 arranged in the manner noted above. In this 

 species, as in most other Zoantharia, the tentacles 

 of contiguous rows alternate. Cerianthus and 

 Saccanthus, however, possess two distinct circlets 

 of tentacles, the one oral, arising close round the 

 mouth, the other marginal, not far from the edge 

 of the disc, the tentacles of the inner row being 



