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 setse 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 setse 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 



FIG. 7. First maxilla of A, Cancer, XI, B, Hapalocarcinus, X70. Second maxilla of C, Cancer, 

 XI. 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 setae 

 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. 



