Hapalocarcinus, the Gall-forming Crab, etc. 55 
forming crab. But on examination I found its stomach to be full of 
fragments, organic and inorganic, which showed a varied diet, and whose 
possible source was rather a puzzle to me. The walls of the stomach, 
moreover, showed a typical armature well fitted for mastication. The 
buccal appendages, though peculiar in some respects, showed little 
evidence of reduction in any way comparable to that in Hapalocarcinus. 
Similarly, I examined the stomach of Synalpheus brucei, which I 
describe in another paper as a commensal with crinoids on the Pacific 
coral reefs, living for the most part if not entirely within the circle of 
their arms. It was in all cases crammed full of foraminifera, radiolaria, 
spicules of calcareous and siliceous sponges, and crustacean fragments, 
as well as pieces of coral skeleton. This examination showed how wide 
is the dietary of these quasi-sedentary creatures. 
While no other member of the Decapoda shows similar modifications 
of the alimentary apparatus, there is a curious similarity between the 
oral appendages of Hapalocarcinus and those of an entire division of 
the lower Crustacea, the Branchiopoda. The following quotation 
from Sedgwick’s Textbook of Zoology (Article Crustacea, by J. J. 
Lister, p. 369) summarises the conditions prevailing in the latter group: 
“Tt is remarkable that while the thoracic appendages of the Branchiopods 
conform so uniformly to a common and, as it appears, primitive type of struc- 
ture, the appendages about the mouth present the greatest divergence from 
that type which is met with in any group of Crustacea. The absence of the 
mandibular palp in the adult is all the more striking because of its size and 
frequently biramous character in other Entomostracan groups, the Copepods 
and the Ostracods. Again the two pairs of maxilla, which even in the Mala- 
costraca conform more closely than any other appendage to the primitive 
‘phyllopod’ type of limb, are here, in the Branchiopods themselves, perfectly 
simple lobes, and one pair is often missing. In adult Cladocera and in Lim- 
netis among the Conchostraca there is only one pair; in Branchipus the second 
pair is rudimentary, and in this genus, as also in Apus, where two pairs are 
present, they are retarded in development, appearing later than the thoracic 
appendages which follow them in position. . . . The late appearance of 
the maxille is perhaps a confirmation of the view taken here that the simple 
condition of those appendages in the Branchiopods is a specialised and not 
a primitive character. The small size and simple character of the maxille 
is perhaps dependent on the peculiar habit of members of this genus . . . of 
passing the food forwards along the ventral groove.” 
The absence of the mandibular palp and the reduction of both pairs of 
maxille to a simple lobe are thus characters common to both the crab 
and the tiny Entomostracans. Lister concludes that this condition 
is secondary in the Branchiopoda and a similar conclusion with regard 
to Hapalocarcinus can not be avoided. Without doubt, also, the 
reduction in both cases is associated with particular habits of food 
collection, but the explanation in the last paragraph of the quotation 
is hardly adequate. A few remarks on the method of feeding in the 
Branchiopoda may be made before instituting a comparison with 
