ORGANS OF DIGESTION. 357 



lated palpi ; the three inferior or outer pairs of maxillee are 

 the largest and the most convertible in their forms, and 

 support branchiee at their base like the ambulatory feet. The 

 entrance of the mouth presents an upper lip, a bifid tongue, 

 and sometimes a small under lip, formed by a pair of maxillae. 

 The .maxillae are often reduced to one or two pairs, or are 

 wanting, in the lower Crustacea. One or more of the anterior 

 pairs of ambulatory feet generally terminate in strong pincers 

 like the palpi of the scorpions. The wide buccal cavity of 

 the decapods, surrounded with complicated organs of sense 

 and of mastication, opens by a very short and narrow oeso- 

 phagus into a capacious stomach, provided internally with 

 several pairs of solid calcareous teeth, and occupying the 

 anterior part of the cephalo thorax. As their watery element 

 almost bathes this gastric cavity, they require no salivary 

 glands to soften their moist food. The gastric teeth, colored 

 and shed like the exterior shell, are symmetrically disposed 

 near the pylorus, and are supported by thin elastic calcareous 

 laminae, to which powerful muscles are attached, and which 

 cause the teeth to meet with precision in grinding the con- 

 tents of the stomach. In many of the parasitic species 

 attached to the surface of fishes, the mouth forms an extended 

 syphon composed of the prolonged lips, and embracing the 

 long, sharp, piercing mandibles, and in the limuli all the 

 masticating organs around the mouth have the form of ambu- 

 latory feet, terminating in pincers. 



As in most other carnivorous articulata, the alimentary 

 canal of the Crustacea passes, without convolutions, through 

 the longitudinal axis of the body, and opens by distinct 

 apertures at its two extremities. The mucous coat forms 

 often rugae or folds in the wide oesophagus and stomach, but 

 passes smooth through the rest of the canal ; the muscular 

 layer is strongest at the orifices of the stomach, and the 

 peritoneal covering, as in insects, forms no mesentery in the 

 abdomen. The pyloric extremity of the stomach, near which 

 the gastric teeth are disposed, receives on each side a short 

 and wide duct from the large and lobated liver which en- 

 velopes this part of the cavity and the beginning of the 

 intestine. The gastric teeth are common to the Crustacea 

 with insects and other articulata, and many molluscous 

 animals. The hepatic duct on each side of the narrow 



