. Carnegie Institution of Washington publication. 52 Papers from the Department of Marine Biology. In accordance with the forward shifting of the sieving apparatus the structure of the pyloric chamber is very simple. The plates which are plentifully developed in other Brachyura are represented here only by one or two vestiges; sieves of setae are almost entirely absent and the pyloric ampullae which are so prominent a feature elsewhere are quite unrepresented. As Mocquard states, in his comprehensive survey of the variations of the stomach in the Decapoda, numerous differences in the various g
. Carnegie Institution of Washington publication. 52 Papers from the Department of Marine Biology. In accordance with the forward shifting of the sieving apparatus the structure of the pyloric chamber is very simple. The plates which are plentifully developed in other Brachyura are represented here only by one or two vestiges; sieves of setae are almost entirely absent and the pyloric ampullae which are so prominent a feature elsewhere are quite unrepresented. As Mocquard states, in his comprehensive survey of the variations of the stomach in the Decapoda, numerous differences in the various groups and successive degradations are experienced, yet I have not been able to find in his descriptions and figures of Brachyura, or in such likely cases as I have myself examined, any in which the modifi- cation is so great as that occurring in Hapalocarcinus. THE CONTENTS OF THE STOMACH. It must of course be recognised that the stomach is very minute (about mm. in breadth), so that it could not in any case contain very large fragments. But when I examined the stomachs of a dozen U. FIG. 10.—Stomach of Hapalo- carcinus; side view. X55. C cardiac and P pyloric divis- ions of the stomach. , pyloric valve; R, alternat- ing ridges and rows of setse between, on the ventral wall of the stomach; S, seta? on lateral walls; T, a group of small tubercles; U uro- cardiac and Z zygocardiac ossicles. or so gall crabs, all but one appeared completely empty; in that one there were a few tiny representatives of the phytoplankton. This was in spite of the fact that the specimens were mounted after dehydrating without staining straight in Canada balsam and then examined with a Ty objective, so that even representatives of the nannoplankton should not have escaped notice. This condition may be explained by a consideration of the probable course by which food reaches the mesenteron. In the first place, the food must consist of organisms contained in the currents of water drawn into the
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