ACEPHALA NUDA. 
115 
external extremities of these rays, and the anus terminates in a com- 
mon cavity, whicli is in tlie 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. 
Pv ROSGMA, Peron. 
The Pyrosomae 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 comiJared to a great number of stars of Bo- 
trylli strung together, the whole of which is moveable |. 
The Mediterranean, and the Ocean, prodiice 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 Mollusca, 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 under the name of 
POLYCLINUM^. 
Some of them are extended over bodies like fleshy crests **. 
* See Desmarets and Lesueur, Bullet, des Sc. May 1815; — Botryllus sfeUatus, 
Gsertner, or Alcyonium Schlosseri, Gm., Pall., Spic. Zool., X, iv, 1 — 5. 
t Botryllus conylomeratus, Gxrt., or Alcyonium conglomeration, Gm.; Pall., Spic. 
Zool. X, iv, 6. 
X See Desmarets and Lesueur, loc. cit. 
§ Several of the Polyclina and Aplidia of Savigny. 
i| Pyrosoma utlanticum, P^ron., Ann. du Mus., IV, Ixxii ; — Pyrosoma gigas, 
Desmar., and Lesueur, Bullet, des Sc. June 1815, pi. v, f. 2. 
^ The Pyrosome iligant, 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 the branchise, stomach, and ovary, that M.de Savigny has formed his Po- 
i.YCLiNUM, Aplidium, Didemmum, Euc.elium, Diazona, Sigillina, &c. which, 
in our opinion, need not be retained. Here, also, should come the Alcyonium ficus, 
Gm. ; the Distomus runoZosMS, Gaertn., or Alcyonium ascidio'itles, Gm., Pall., Spic. 
Zool., X, IV, 7. 
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