50 



Papers from the Department of Marine Biology. 



That which is significant is not that the endopodite has become slender, 

 but that the appendages have been forced so far apart. 



The second and first maxillipeds are fairly typical and call for no par- 

 ticular remark beyond the description of Caiman. 



The second maxilla consists firstly of a small triangular plate, the 

 base of which is free and directed inwards, which represents the proto- 

 podite, not divided into a basipodite and coxopodite as in Cancer 

 (where each again is bilobed). The inner border is provided with 

 many setae. Internally the appendage passes into a narrow neck, 

 where a second bunch of setae is given off and where a possible articu- 

 lation occurs. Secondly, there is an exopodite, the scaphognathite, 

 which attains the development usual in the Brachyura. The con- 

 nection between the protopodite and the exopodite is very slender, thus 

 differing from that in Cancer and other crabs. The protopodite sub- 

 serves nutrition and its rudimentary character is thus strongly con- 

 trasted with the normal devel- 

 opment of the exopodite, which 

 performs a respiratory func- 

 tion. The partial disconnec- 

 tion of these two parts which 

 appears to be in progress is 

 perhaps due to the fact that 

 their rhythmical movements 

 do not coincide. The endopo- 

 dite, found in other Brachyura, 

 is wanting here. 



The first maxilla shows a 

 much greater reduction, since 

 it is entirely masticatoiy in function. It is represented by a slightly 

 curved, slender plate representing the protopodite. It is less than a 

 quarter of the size of that of the second maxilla. It is undivided in 

 contrast to the bilobed protopodite of other Brachyura. A few setae 

 are present internally. The endopodite is absent. 



The mandibles are two smooth triangular plates, thin but more 

 strongly chitinised than the other buccal appendages, with straight 

 internal edges, not broad or much thickened, so as to serve for mastica- 

 tion, but capable of working over each other. Internally on each side 

 is an apophysis for the attachment of the mandibular muscle. These 

 appendages are evidently quite effective ones, though they are plainly 

 not used for crushing organisms or food particles, as is usual in the 

 Brachyura. Their operations may be confined to sifting or current 

 creating. The absence of a palp is a very noticeable feature. 



THE STOMACH. 



The stomach of Hapalocarcinus differs distinctly from the type nor- 

 mally found in the Brachyura. In all the higher Crustacea the stomach 



B 



FIG. 8. Mandible of A, Cancer, X 1 ; 

 B, Hapalocarcinus, X70. 



