CHAP. XVII. STKUCTUEE OF THE BLADDER. 



399 



the outside, six or seven long, pointed, multicellular 

 bristles. These prolongations of the bladder may be 

 conveniently called the antennae, for the whole bladder 

 (see fig. 17) curiously resembles an entoinostracan crus- 

 tacean, the short footstalk representing the tail. In 

 fig. 18, the near antenna alone is shown. Beneath 

 the two antennae the end of the bladder is slightly 

 truncated, and here is situated the most important 

 part of the whole structure, namely the entrance and 

 valve. On each side of the entrance from three to 

 rarely seven long, multicellular bristles project out- 



FIG. 19. 



(Utriculana neglecta.) 

 Valve oi bladder ; greatly enlarged. 



wards ; but only those (four in number) on the near 

 side are shown in the drawing. These bristles, to- 

 gether with those borne by the antennae, form a sort 

 of hollow cone surrounding the entrance. 



The valve slopes into the cavity of the bladder, or 

 upwards in fig. 18. It is attached on all sides to 

 the bladder, excepting by its posterior margin, or the 

 lower one in fig. 19, which is free, and forms one side 

 of the slit-like orifice leading into the bladder. This 

 margin is sharp, thin, and smooth, and rests on the 

 edge of a rini or collar, which dips deeply into the 



