Cap. XVII] ABSORPTION BY THE GLANDS. 337 
fluid habitually passes outwards. But we must remember that 
a bladder generally captures several animals; and that each 
time a fresh animal enters, a puff of foul water must pass 
out and bathe the glands. Moreover, I have repeatedly 
found that, by gently pressing bladders which contained air, 
minute bubbles were driven out through the orifice; and if 
a bladder is laid on blotting paper and gently pressed, water 
oozes out. In this latter case, as soon as the pressure is 
relaxed, air is drawn in, and the bladder recovers its proper 
form. If it is now placed under water and again gently 
pressed, minute bubbles issue from the orifice and nowhere 
else, showing that the walls of the bladder have not been 
ruptured. I mention this because Cohn quotes a statement 
by Treviranus, that air cannot be forced out of a bladder 
without rupturing it. We may therefore conclude that 
whenever air is secreted within a bladder already full of 
water, some water will be slowly driven out through the 
orifice. Hence I can hardly doubt that the numerous glands 
crowded round the orifice are adapted to absorb matter from 
the putrid water, which will occasionally escape from 
bladders including decayed animals. 
In order to test this conclusion, I experimented with various 
solutions on the glands. As in the case of the quadrifids, salts of 
ammonia were tried, since these are generated by the final decay of 
animal matter under water. Unfortunately the glands cannot be 
carefully examined whilst attached to the bladders in their entire 
state. Their summits, therefore, including the valve, collar, and 
antenna, were sliced off, and the condition of the glands observed; 
they were then irrigated, whilst beneath a covering glass, with the 
solutions, and after a time re-examined with the same power as before, 
namely No. 8 of Hartnack. The following experiments were thus 
made. 
As a control experiment solutions of one part of white sugar and of 
one part of gum to: 218 of water were first used, to see whether these 
produced any change in the glands. It was also necessary to observe 
whether the glands were affected by the summits of the bladders having 
been cut off. The summits of four were thus tried; one being exam- 
ined after 2 hrs. 30 m., and the other three after 23 hrs.; but there 
was no marked change in the glands of any of them. 
Two summits bearing quite colourless glands were irrigated with a 
solution of carbonate of ammonia of the same strength (viz. one part 
to 218 of water), and in 5 m. the primordial utricles of most of the 
glands were somewhat contracted; they were also thickened in specks 
or patches, and had assumed a pale brown tint. When looked at 
Z 
