ACTINIA. ACALEPHA. 411 



CLASS XII. ACALEPHA. 



Body gelatinous, circular and radiated, with the skin soft 

 and transparent, susceptible of contraction and dilatation. 



THE class Acalepha of Cuvier embraces the Radiaires Me- 

 dusaires and Anomales of Lamarck, and besides includes the 

 genus Actinia, which the latter author had placed in a division 

 of his Echinodermata. 



The animals of this class are either fixed by a base, or float 

 freely in the ocean, and many are suspended in the water by 

 the specific lightness of some of their parts, or by the air contained 

 in their bodies. Their substance is gelatinous, without appa- 

 rent fibres, though susceptible of contraction and dilatation. 

 The sort of vessels found in some are merely canals in the ge- 

 latinous substance, connected with the stomach ; none of their 

 movements seem connected with muscular action ; there is no 

 proper cavity for containing organs ; the mouth or the suckers 

 or tentacula in the centre of the inferior surface is unprovided 

 with hard parts ; and the stomach, or the organ of digestion and 

 nutrition, is a simple sac without outlet. Between this sac and 

 the external skin is a complicated but obscure organization. 

 The Acalepha shine during the night with a phosphoric lumi- 

 nosity. Many species are ornamented with lively colours. 

 .They are common in all seas. Cuvier divides the class into 

 two Orders, viz. 1. Those where the body is fixed by a base, 

 either permanently or occasionally ; and 2. Those which float 

 freely in the ocean. 



SECTION I. Body fixed. 



This division comprehends those soft animals which fix themselves by their base. 

 Though thus fixed, however, they have the power of crawling upon this base, or de- 

 taching it altogether, and of swimming or allowing themselves to be carried by the 

 water ; but the motion is generally limited to the expansion of the opening of 

 their mouth, which serves also for an anus. This mouth is surrounded by ten- 

 tacula, more or less numerous, and opens into a stomach without other outlet 

 Between this interior sac and the exterior skin is a complicated but obscure orga- 

 nization, consisting of vertical and fibrous leaflets, to which the ovaries adhere, si- 

 milar to twisted threads. 



Gen. 1. ACTINIA, Lam. 



Body cylindrical, fleshy, simple, very contractile, fixed by its 

 base, but having the faculty of displacing itself; mouth termi- 



