XXIV 



INTRODUCTION. 



been shown to consist of six pairs, of which some are actual 

 organs of mastication, as the mandibles or the true jaws, 

 the foot-jaws or pedipalps generally serving to keep the 

 food in contact with the former, whilst it is being broken 

 up by them. 



The buccal orifice in the Brachyura occupies the in- 

 ferior face of the cephalic division of the body, and is 

 bounded anteriorly by a crustaceous lamina of determi- 

 nate form, which has been termed the upper lip, and pos- 

 teriorly by another termed the lower lip. The mandibles 

 occupy the sides of the opening. After these, and ex- 

 ternal to them, are the first, and then the second pair of 

 true jaws, followed by the three pairs of pedipalps or 

 foot-jaws, the last of which, when at rest, close the mouth, 

 and include the whole of the preceding ones. In the 

 Macroura, the pedipalps are very different in their forms, 

 and have the aspect of very simple feet. In the Stoma- 

 poda they not only have the form, but the office also of 

 the other locomotive organs, and hence the increased 

 number of legs which appear to appertain to these, and 

 especially to the Mysidae. In the Edriophthalma, and the 

 other lower forms, the parts about the mouth are fewer, 

 and more simple. At the back of the mouth, a short 

 O3sophagus opens into the stomach, which is a very ca- 

 pacious cavity, occupying the whole depth of the body in 

 the Decapods, and co-extensive with the gastric region of 

 the carapace, already described. It is pretty distinctly 

 divided into two portions, a cardiac and a pyloric, the 

 former occupying the greater portion of the cavity, the 

 latter of small dimensions. 



The means of comminuting the food are not restricted 

 to the complicated machinery above referred to, for the 



