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 0.5 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. P.V., 

 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 

 T y 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 gall through the respiratory apertures. It is hardly 

 necessary to repeat the statement of early observers that the crab 

 does not devour the coral polyps. Moreover, the smaller members of 

 the plankton alone can enter the gall (in the closed galls at least) and 

 I have little doubt that the bulk of the food consists of the so-called 



