Hapalocarcinus, the Gall-forming Crab, ete. 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 
Fic. 5.—Various types of buccal areas in the Brachyura. 
A. Cancer, X1. 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; Mzx2, 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 
