Chap. XVIIL] STRUCTURE OF THE BLADDERS. 351 



in not being armed with bristles. Their bases are so ab- 

 ruptly curved that their tips generally rest one on each side 

 of the middle of the bladder, but sometimes near the margin. 

 Their curved bases thus form a roof over the cavity in which 

 the valve lies; but there is always left on each side a little 

 circular passage into the cavity, as may be seen in the draw- 

 ing, as well as a narrow passage between the bases of the 

 two antennse. As the bladders are subterranean, had it not 

 been for the roof, the cavity in which the valve lies would 



Fig. 27. 



( Utrieularia moniana.) 



Bladder; about 27 times enlarged. 



have been liable to be blocked up with earth and rubbish ; so 

 that the curvature of the antennse is a serviceable character. 

 There are no bristles on the outside of the collar or peristome, 

 as in the foregoing species. 



The valve is small and steeply inclined, with its free pos- 

 terior edge abutting against a semicircular, deeply depend- 

 ing collar. It is moderately transparent, and bears two pairs 

 of short stiff bristles, in the same position as in the other 

 species. The presence of these four bristles, in contrast with 

 the absence of those on the antennae and collar, indicates 

 that they are of functional importance, namely, as I believe, 



