Hapalocarcinus, the Gall-forming Crab, etc. 



47 



example of the class of microphagous organisms and shows the kind of 

 modifications which occur in them. In the account which follows I 

 have compared those structures, where difference is exhibited, with the 

 typical forms in the Brachyura. 



THE GENERAL CONFIGURATION OF THE BUCCAL AREA. 



In the Decapoda Brachyura the third maxilliped is so enlarged as to 

 cover the whole of the buccal area. In Cancer, for instance, the two 

 appendages form a pair of folding doors meeting exactly in the middle 

 line and when they are closed the mouth and all the buccal appendages 

 are completely hidden from view. In the endopodite the ischiopodite 

 and meropodite are much broader than the more distal joints and 

 together with the basal joint of the exopodite they form the greater 

 part of a rectangle so perfect that the inner borders can meet exactly 



.mp 2 



ex.mp.l 



FIG. 5. Various types of buccal areas in the Brachyura. 



A. Cancer, XI. B. Pinnotheres, X3.5. C. Hapalocarcinus, X85. 



ex. mp. 1. ex. mp.2. ex. mp. 3. exopodites of maxillipeds 1, 2, and 3; 



B', C", basipodite and coxopodite of maxilliped 1; Mx2, maxilla 2; Md., mandible. Other 

 letters as in text-fig. 16. 



In A and B the other appendages are completely covered by the third maxilliped, and so 

 they are not indicated in any way. In C, which is drawn from a specimen cleared in potash and 

 mounted in Canada balsam, a great number of the buccal appendages are clearly visible and the 

 character of the preparation allowed me to indicate by dotted lines the parts which were 

 overlapped. 



and the outer make straight hinge lines. This well-fitting apparatus 

 ensures that the food, where this is taken in large pieces, can be masti- 

 cated without the particles escaping. In some Brachyura, members of 

 the Oxyrhyncha (e. g., Stenorhynchus and Inachus), where, owing to the 

 shape of the cephalothorax, the buccal area is greatly diminished in 

 width, there is not this excessive broadening of the two basal joints of 

 the endopodite. In Stenorhynchus the meropodite is no wider than the 

 succeeding joints, while the ischiopodite is but slightly broadened and 

 has a curved inner border. But the three distal joints bend downwards 



