142 THE OCEAN WORLD. 



inches in length, and from one to three broad. Its appearance is 

 glassy and transparent, its colour an imperfect purple, passing to a 

 violet, then to an azure above. It is surmounted by a crest, limpid 

 and pure as crystal, veined with purple and violet in decreasing 

 tints. Under the vesicle float the fleshy filaments, waving and 

 contorted into a spiral form, which sometimes descend perpendi- 

 cularly like so many threads of celestial blue. Sailors beUeve that 

 the crest which surmounts the vesicle performs the office of a sail, 

 and that it tells the navigator "how the wind blows," as they say. 

 This bladder-like form, with its aerial crest, is only a hydrostatic 

 apparatus, whose office is to lighten the animal, and modify its 

 specific gravity. 



" This bladder," says Gosse, in his " Year by the Sea-side," " is 

 filled with air, and therefore floats almost wholly on the surface. 

 Along the upper side, nearly from end to end, runs a thin edge 

 of membrane, which is capable of being erected at will to a 

 considerable height, fully equal at times to the entire width of the 

 bladder, when it represents an arched fore-and-aft sail, the bladder 

 being the hull. From the bottom of the bladder, near the thickest 

 extremity, where there is a denser portion of the membrane, depends 

 a crowded mass of organs, most of which take the form of ^'ery 

 slender, highly contractile, movable threads, which hang down 

 into the deep to a depth of many feet, or occasionally of several 

 yards. 



" The colours of this curious creature are very vivid ; the bladder, 

 though in some parts transparent and colourless, and in some 

 specimens almost entirely so, is in general painted with richest blue 

 and purple, mingled with green and crimson to a smaller extent, 

 these all being, not as sometimes described, iridescent or changeable, 

 but positive colours independent of the incidence of light, and, for 

 the most part, possessing great depth and fulness. The sail-like 

 erectile membrane is transparent, tinted towards the edge with a 

 lovely rose-pink hue, the colours arranged in a peculiar fringe-like 

 manner. When examined anatomically, the bladder is found to be 

 composed of two walls of membrane, which are lined with cilia, and 

 have between them the nutritive fluid which supplies the place of 

 the blood. Besides this, the double membrane is turned in ox 

 inverted like a stocking prepared for putting on ; and thus there is a 

 bladder within a bladder, both having double walls ; the inner 

 iypneumatocyst) much smaller than the outer {pneimiatophore), and con- 

 tracted at the point where it is turned into the almost imperceptible 

 orifice. The inner sends up closed tubular folds into the crest, 



