112 CLASS III. 



Salacia, for thus LINN^US announced it in the earlier editions of his 

 Syst. Nat. ; in the tenth and following editions it is no longer met 

 with, and LINNJEUS afterwards arranged the species known to him 

 under the genus Holothuria. 



VON OLFERS especially threw much light upon the organisation of 

 this genus by the investigation of Physalia caravella ESCHSCH. (Phys. 

 arethusa TILES.) A Physalia has two bladders, the internal is 

 filled with air, and was described by OLFERS as perfectly closed; the 

 external has an aperture situated at one extremity and surrounded 

 by a sphincter. 



[QUATREFAGES 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 Physsophoridce require further investigation. 



See v. OLFERS in Physical. Abhavdl. der Koniyl. Akademic der Wissenscft. 

 zu Berlin a. d. Jahre 1831, Berlin 1832, s. 155 200. 



Comp. also on this genus J. C. VAN HASSELT in Algem. Kunst. en Letter- 

 bode 1828, No. 44, 45 ; F. W. EYSENHABDT, Nov. Act. Acad. Ca>s. Leop. 



1 Ann. des Sc. not. 30 Se'rie, Tom. 11. p. 1 15. 



