THE BLADDERS IN UTRICULARIA VULGARIS. 407 
within the bladder causes an influx of water. The influx being completed, 
the valve once more springs back to its former position. Such appears to 
be the mechanism, as far as my observations go. Brocher suggested a 
straightening of the valve instead of an upward movement. He did not 
observe that the valve margin was retained in any particular way, but thought 
that it was merely closely adpressed to the collar. 
Fre. 5 
Section of opening of bladder, enlarged. x 200. 
Reasons FOR FOREGOING THEORY OF MECHANISM. 
It has been suggested that absorption of internal water is carried on by the 
quadrifid hairs lining the bladder. These seem to be the most likely agents. 
Previous investigators came to the conclusion that these hairs were absorptive, 
and, indeed, there seems to be no reason for doubt. They certainly absorb 
methylene blue very rapidly, and that they are probably homologous with 
the mushroom-shaped glandular hairs of Pinguicula adds weight to the 
suggestion of their absorptive nature. 
That there is a negative pressure within the bladder seems to me to be 
proved by the fact that if a concave (sensitive) bladder is pierced with a 
needle, the walls immediately spring outwards and back to their convex 
