Chap. XVII.] STRUCTURE OF THE BLADDER. 325 



are also on the surface of the valve niunerous glands, as I 

 will call them; for they have the power of absorption, 

 though I doubt whether they ever secrete. They consist of 

 three kinds, which to a certain extent graduate into one 

 another. Those situated round the anterior margin of the 

 valve (upper margin in Fig. 19) are very numerous and 

 crowded together; they consist of an oblong head on a long 

 pedicel. The pedicel itself is formed of an elongated cell, 

 surmounted by a short one. The glands towards the free 

 posterior margin are much larger, few in number, and almost 

 spherical, having short footstalks; the head is formed by the 

 confluence of two cells, the lower one answering to the short 

 upper cell of the pedicel of the oblong glands. The glands of 

 the third kind have transversely elongated heads, and are 

 seated on very short footstalks; so that they stand parallel 

 and close to the surface of the valve; they may be. called 

 the two-armed glands. The cells forming all these glands 

 contain a nucleus, and are lined by a thin layer of more or 

 less granular protoplasm, the primordial utricle of Mohl. 

 They are filled with fluid, which must hold much matter in 

 solution, judging from the quantity coagulated after they 

 have been long immersed in alcohol or ether. The depression 

 in which the valve lies is also lined with innumerable glands ; 

 those at the sides having oblong heads and elongated 

 pedicels, exactly like the glands on the adjoining parts of 

 the valve. 



The collar (called the peristome by Cohn) is evidently 

 formed, like the valve, by an inward projection of the walls 

 of the bladder. The cells composing the outer surface, or 

 that facing the valve, have rather thick walls, are of a 

 brownish colour, minute, very numerous, and elongated; the 

 lower ones being divided into two by vertical partitions. 

 The whole presents a complex and elegant appearance. The 

 cells forming the inner surface are continuous with those 

 over the whole inner surface of the bladder. The space be- 

 tween the inner and outer surface consists of coarse cellular 

 tissue (Fig. 20). The inner side is thickly covered with 

 delicate bifid processes, hereafter to be described. The collar 

 is thus made thick; and it is rigid, so that it retains the 

 same outline whether the bladder contains little or much air 

 and water. This is of great importance, as otherwise the 



