ACKPHALA NUDA. 115 



external extremities of tliese rays, and the anus terminates in a com- 

 mon cavity, wliich is in the centre of the star. If an orifice be irri- 

 tated, but a single animal contracts ; if the centre be touched they all 

 contract. These very small animals attach themselves to certain 

 Ascidiae, Fuci,&c*. 



In some particular species, three or four stars appeared to be piled 

 one on the other f. 



Pyrosoma, Peron. 



The Pyrosomije unite in great numbers, forming a large hollow 

 cylinder, open at one end and closed at the other, which swims in 

 the ocean by the alternate contraction and dilatation of the individual 

 animals which compose it. The latter terminate in a point on the 

 exterior, so that the whole external surface of the tube is bristled 

 with them ; the branchial orifices are pierced near these points, and 

 the anus debouches in the internal cavity of the cylinder. A 

 Pyrosoma may thus be compared to a great number of stars of Bo- 

 trylli strung together, the whole of which is moveable J. 



The Mediterranean, and the Ocean, produce large species, the 

 animals of which are arranged with but little regularity. They 

 exhibit a phosphorescent appearance during the night §. 



A smaller species is also known ||, where the animals are 

 arranged in very regular rings. 



The remainder of these aggregated MoUusca, like the ordinary 

 Ascidiae, have the anus and branchial orifice approximated to the 

 same etremity. The species known are all fixed, and till now they 

 have been confounded with the Alcyonia. The visceral bundle of 

 each individual is more or less extended into the common cartilaginous 

 or gelatinous mass, more or less narrowed or dilated in certain points ; 

 but each orifice always forms a little six-rayed star on the surface. 

 We unite them all xinder the name of 



PoLYCLINUM^f. 



Some of them are extended over bodies like fleshy crests **. 



* See Desmarets and Lesueur, Bullet, des Sc. May 1S15; — BotryUus stellatus, 

 Gaertner, or Alcyonium Schlosseri, Gm., Pall., Spic. Zool., X, iv, 1 — 5. 



f BotryUus conyhmeratus, Gdtrt., ot Ahyonium conglomeratum, Gm.; Pall., Spic. 

 Zool. X, iv, 6. 



X See Desmarets and Lesueur, loc. cit. 



§ Several of the Polyclina and ApUdia of Savigny. 



II Pyrosoma aUanticum, P^ron., Ann. du Mus., IV, Ixxii ; — Pyrosoma gigas, 

 Desmar., and Lesueur, Bullet, des Sc. June 1815, pi. v, f. 2. 



*[ The Pyrosome elegant, Lesueur, Bullet, des Sc., June 1815, pi. v, f. 2. 



** It is from the number of strangulations, that is to say, the greater or less 

 separation of thebranchiae, stomach, and ovary, that M.de Savigny has formed his Po- 

 LYCLiNUM, Aplidium, Didemmum, Euc-elium, Diazona, Sigillina, itc. which, 

 in our opinion, need not be retained. Here, also, should come the Alcyonium fins, 

 Gm. ; the Distomus variolosus, Gxrtn., or Alcyonium ascidwides, Gm., Pall., Spic, 

 ZooJ,, X, IV, 7. 



i2 



