Hapalocarcinus, the Gall-forming Crab, etc. 49 
is no wider than the following joints. The last three are not bent pos- 
teriorly, as is usually the case, to aid in closing the buccal cavity, but are 
directed anteriorly and towards each other, while the setze with which 
they are plentifully provided project internally. It will, then, be 
seen by reference to figure 9 that the buccal area is entirely uncovered 
and is only screened by a series of fringes of setae borne successively 
by the endopodite of the third and the exopodites of the second and 
first maxillipeds. Together they form an efficient sieve. So far, then, 
from the buccal area being carefully guarded and closed lest the pro- 
ducts of mastication should escape, free access is given to the mouth. 
The constant circulation of water is thus promoted and the mobile parts 
of the maxillipeds are given free play to separate out from the respira- 
tory current those very minute organisms which form the food of 
Hapalocarcinus. 
THE BUCCAL APPENDAGES. 
The third maxillipeds have already been discussed in the last section. 
In text-figure 6 these appendages are shown in Hapalocarcinus, 
Porcellana, and Stenorhynchus. The peculiar feature of the appendage 
Fic. 7.—First maxilla of A, Cancer, X1, B, Hapalocarcinus, X70. Second maxilla of C, Cancer, 
1. D, Hapalocarcinus X70; b, basipodite; c, coxopodite; e, endopodite; p, undivided pro- 
topodite; s, scaphognathite. 
in the first genus is undoubtedly the rudimentary character of the 
exopodite, a feature not found elsewhere in the Decapoda Brachyura. 
Its absence is compensated for by the development of the distal joints 
of the endopodite, which instead of being turned backwards to form an 
insignificant trapdoor arrangement over the buccal area are compar- 
atively stout and long, being directed inwards so that each meets its 
fellow of the other side, and with a much greater development of setze 
than in other Brachyura. The ischiopodite is curiously shaped, it is 
true, but it still has a dilated form which in my opinion shows its 
descent from a Brachyuran stock in which the buccal area was broad 
and completely covered by the third maxilliped. The meropodite is 
slender, but so it is (and the ischiopodite as well) in Stenorhynchus. 
