ACALEPH^E. 245 



surmounts the vesicle performs the office of a sail, and that they tell 

 the navigator "how the wind blows," as they say. With all respect to 

 the sailors, the bladder-like form, with its aerial crest, is only a hydro- 

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

 specific gravity. Mr. Gosse thinks otherwise, however. 



" 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 repre- 

 sents 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 very 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 blues 

 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 food which supplies the place of the blood. Besides 

 this, the double membrane is turned in or inverted like a stocking 

 prepared for putting- on; and thus there is a bladder within a 

 bladder, both having double walls ; the inner (pneumatocyst) much 

 smaller than the outer (pneumatophone), and contracted at the point 

 where it is turned into the almost imperceptible orifice. The inner 

 sends up closed tubular folds into the crest, which, being arrested by 

 the membranous walls of the outer sac, give to the sail that 

 appearance of vertical wrinkles which is so conspicuous." 



When it is filled with air the body is almost projected out of the 

 water. In order to descend it is necessary to compress itself or dispel 



