402 UTKICULAKIA NEGLECTA. Chap. XVII 



tween the inner and outer surface consists of coarse 

 cellular tissue (fig. 20). The inner side is thickly 

 covered ^yith 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 thin and 

 flexible valve would be liable to be distorted, and 

 in this case would not act properly. 



Altogether the entrance into the bladder, formed by 

 the transparent valve, with its four obliquely project- 

 ing bristles, its numerous diversely shaped glands, 

 surrounded by the collar, bearing glands on the 

 inside and bristles on the outside, together with the 

 bristles borne by the antennae, presents an extra- 

 ordinarily complex appearance when viewed under 

 the microscope. 



We will now consider the internal structure of the 

 bladder. The whole inner surface, with the exception 

 of the valve, is seen under a moderately high power to 

 be covered with a serried mass of processes (fig. 21). 

 Each of these consists of four divergent arms ; whence 

 their name of quadrifid processes. They arise from 

 small angular cells, at the junctions of the angles of 

 the larger cells which form the interior of the 

 bladder. The middle part of the upper surface of these 

 small cells projects a little, and then contracts into a 

 very short and narrow footstalk which bears the four 

 arms (fig. 22). Of these, two are long, but often of not 

 quite equal length, and project obliquely inwards and 

 towards the posterior end of the bladder. The two 

 others are much shorter, and project at a smaller angle, 

 that is, are more nearly horizontal, and are directed 

 towards the anterior end of the bladder. These arms 

 are only moderately sharp ; they are composed of ex- 



