404 DR. C. L. WITHYCOMBE ON THE FUNCTION OF 
and elongate oval in shape ; their length lies in the same direction as that of 
the collar. The cells are not fused with each other, but are in close proximity. 
In longitudinal section of the bladder (fig. 2) it is seen that uppermost is a 
layer of apparently columnar cells (fig. 5, ul), the cells having been cut across 
their width. Below this is a thin middle layer of smaller cells (fig. 5, mt). 
Again, below the middle layer is a basement layer of cells (fig. 5, be), rather 
similar to the upper layer and continuous with the epidermis of the bladder. 
Projecting into the bladder cavity from the posterior (interior) margin of the 
collar are some elongate hairs (fig. 3,e and fig. 5,eh), and on the extreme 
Fic. 3. 
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Different types of hairs. x 400, 
margin of the collar are several club-shaped hairs (fig. 3,a and fig. 5, ch) 
similar to those on the rest of the rim and on the valve. All these hairs are 
doubtless homologous with the quadrifid absorptive hairs lining the bladder 
cavity. 
The valve or flap (r) closing the bladder mouth is a continuation of the 
dorsal wall of the bladder (fig. 4). It is two cells in thickness, and is of such 
shape as to close the mouth completely when its ventral, free margin is 
applied to the collar. The valve consists of three ill-defined regions. An 
upper, dorsal region with both layers of cells composing it fairly similar. 
