THE BLADDEE. 251 



colourless, and in some specimens almost entirely so, 

 is in general painted with the richest blues and purples, 

 mingled with green and crimson to some less extent ; 

 these all being, not as sometimes described, iridescent 

 or changeable reflections, but positive colours, indepen- 

 dent 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 pecu- 

 liar 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 blood. Besides this, 

 the double membrane is turned in, somewhat as the 

 foot of a stocking is inverted, when ready for putting 

 on ; and thus there is a bladder within a bladder, both 

 having double walls. The inner (pneumalocyst) is 

 much smaller than the outer (pneumatophore) ; and 

 the point where it is turned in is contracted to the 

 almost imperceptible orifice that has been mentioned. 

 The inner bladder sends up closed tubular folds into 

 the crest, which, being invested by the membranous 

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

 of vertical wrinkles which is conspicuous. 



Most formidable are the powers which reside in the 



