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 antennae, 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 examined 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 [page 419] brown tint.  When looked at again after 1 hr. 30 m., most of them presented a somewhat different appearance.  A third specimen was treated with a weaker solution of one part of the carbonate to 437 of water, and after 1 hr. the glands were pale brown and contained numerous granules.

Four summits were irrigated with a solution of one part of nitrate of ammonia to 437 of water.  One was examined after 15 m., and the glands seemed affected; after 1 hr. 10 m. there was a greater change, and the primordial utricles in most of them were somewhat shrunk, and included many granules.  In the second specimen, the primordial utricles were considerably shrunk and brownish after 2 hrs.  Similar effects were observed in the two other specimens, but these were not examined until 21 hrs. had elapsed.  The nuclei of many of the glands apparently had increased in size.  Five bladders on a branch, which had been kept for a long time in moderately pure water, were cut off and examined, and their glands found very little modified.  The remainder of this branch was placed in the solution of the nitrate, and after 21 hrs. two bladders were examined, and all their glands were brownish, with their primordial utricles somewhat shrunk and finely granular.