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Mr Potts, The gall-forming Crab, Hapalocarcinus. 455 
‘been pointed out before how erroneous was the early description 
of Hapalocarcinus as a parasite on corals. There is no doubt that 
the crab must live on the plankton which is drawn in with the 
yespiratory current. But the larger constituents of the plankton 
fauna are too large to enter the apertures of the gall and I suggest 
that the food of Hapalocarcinus consists almost entirely of the 
so-called “nanno-plankton ” which embraces all those animals and 
plants less than 3-4 in measurement. This suggestion is borne 
‘out by my examination, so far as it goes, of the stomachs of a 
dozen or so gall-crabs. These appear empty on a cursory investiga- 
tion but on one or two occasions there were very small repre- 
‘sentatives of the phytoplankton. It is suggested that these 
organisms are collected from the respiratory current in the first 
place by the action of the close-set combs of setae springing from 
the interior of the palps of the maxillipeds which cover the whole 
of the buccal area. The close likeness which exists between the 
oral appendages of Hapalocarcinus and those of the Branchiopoda 
im the lower Crustacea is explained by a similarity of diet. In 
this latter group too, the mandibular palp is absent, the mandible 
is weak, and the maxillae are perfectly simple lobes, one pair 
sometimes being lost altogether. Mr J. T. Saunders, of Christ’s 
College, informs me that these animals undoubtedly feed upon 
nanno-plankton. 
