

MOLLUSCA. 309 



upon a calm sea and beneath the rays of a tropical sun, are 

 surpassingly brilliant and imposing. The pointed extre- 

 mity of its inflated body is dark indigo-blue at its 

 apex, fading to a lighter shade towards the base ; the 

 procumbent crest on the back is pink or flesh-colour ; 

 while the remainder of the vesicle exhibits a play of 

 iridescent colours, amongst which a pale straw-colour 

 and aqua-marine predominate. The colours of the ten- 

 tacular fringe on the lower margin of the body are vivid 

 and strongly contrasted : the outer layer of filaments 

 being crimson, the inner purple. Each long tentacle 

 or cable is transparent, excepting where it is coloured 

 by two slender longitudinal lines, passing through its 

 entire length, and connected by transverse equidistant 

 bars of the same hue, which give it a jointed ap- 

 pearance. 



The inflated membrane of the body is composed of 

 more than one layer ; and, when closely examined, is 

 found to possess longitudinal fibres, which have proba- 

 bly the function of muscles. The chemical character of 

 the air it contains has not been determined; but, 

 judging by analogy, we may suppose it to resemble the 

 air contained in the swim-bladder of marine fishes. 



When floating on the ocean, the body of the Phy- 

 salis has the form of an inverted crescent, both its ex- 

 tremities being depressed, and the back convex. The 

 crest can be raised or depressed at will; and is as 

 often seen under the one as the other condition. It is, 

 when erect, a tall inflated membrane, grooved verti- 

 cally, transparent, and of a delicate pink colour. The 

 animal, when removed from the water, writhes its body 

 into many contorted shapes, and retracts its cables, but 

 displays no power of moving the short tentacles. 



The cables are viscid, and adhere tenaciously to any 

 foreign body. It is in these appendages alone that the 



