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 sete are almost entirely absent and 
the pyloric ampulle 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 
Fie. 10.—Stomach of Hapalo- 
carcinus; side view. X55. 
C cardiac and P pyloric divis- 
ionsofthestomach. P.V., 
pyloric valve; R, alternat- 
ing ridges and rows of set 
between, on the ventral 
wallof thestomach;S, setz 
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 
;'x"’ 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 
