112 
CLASS III. 
Salacia, for thus Lrnnxus announced it in the earlier editions of his 
Syst. Nat. ; in the tenth and following editions it is no longer met 
with, and Linn.mus afterwards arranged the species known to him 
under the genus /olothuria. 
Von Orers especially threw much light upon the organisation of 
this genus by the investigation of Physalia caravella Escuscu. (Phys. 
arethusa Titrs.) A Physalia has two bladders, the internal is 
filled with air, and was described by OLFeERs as perfectly closed ; the 
external has an aperture situated at one extremity and surrounded 
by a sphincter. 
[Quarreraces has described the action of this sphincter muscle, 
and the connexion of both bladders with the aperture ; he also 
caused the air contained in the interior bladder to be analysed, and 
found that it contained less of oxygen than atmospheric air by about 
3 per cent.: the animal appeared to be able to expel the air volunta- 
rily at intervals, and to distend the bladder again after a short time: 
it would therefore seem to be a respiratory organ for the colony: the 
air-bladder is surrounded on all sides by the external bladder or 
envelope, which is in fact the expanded stem of the colony: with the 
under surface of this the various appendages are connected, and into 
its cavity the cavities of them all open more or less directly: the 
bladder in Physalia did not appear to QUATREFAGES' to be merely a 
passive organ, for besides the power of emptying and distending it 
the animal seemed to be able to direct the fluid contained in the 
cavity of the appendages into this or that bundle of them at will, 
and so to alter the position of the center of gravity of the bladder, 
and by thus bringing different regions of it to the surface to steer 
its course. | 
The larger and smaller tentacles are capable of extension and 
contraction, and serve probably for feeling and seizing. Small 
clumps of red corpuscles, which are situated between the larger 
tentacles, are, according to OLFERS, eggs: but the sexual organs of 
the Physsophoride require further investigation. 
See v. OLFERS in Physikal. Abhandl. der Kénigl. Akademie der Wissensch. 
eu Berlina. d. Jahre 1831, Berlin 1832, s. 155—200. 
Comp. also on this genus J. C. Van Hasseur in Algem. Kunst. en Letter- 
bode 1828, No. 44, 48; F. W. Eysennarnpt, Nov. Act. Acad. Cos. Leop. 
' Ann. des Sc, nat. 3e Série, Tom. 1. p. 115. 
