250 BULLETIN OF THE BUREAU OP FISHERIES. 



The stomach is divided into a larger forward, or cardiac division, for storage chiefly, 

 and a smaller hinder, or pyloric section (pi. xxxiii and xxxiv) , mainly for sorting and 

 straining the food. Between the two lies the gastric mill, the grinding ' ' stones ' ' of which 

 consist of a single dorsal median tooth and of two large lateral grinders. The wall of the 

 stomach is composed of two layers of connective tissue, in the inner and looser of which 

 are lodged the blood vessels and muscles, a gastric epithelium, and a chitinous lining. 

 The lining of the stomach is thickened in certain areas and hardened by deposits of lime, 

 to form the calcareous plates or ossicles which make up the framework of the gastric 

 mill; the largest and strongest ossicles culminate in the "millstones," or teeth, just 

 mentioned. The lining of this organ is further thrown into various permanent folds, 

 pads, ridges, or bands, between which lie definite canals for the circulation of Uquids 

 containing the comminuted food. Most of these parts are thickly studded with short 

 setae, which in general point toward the gastric mill, and serve to direct the food mechan- 

 ically into its proper channels, whether to or from the mill, whether into the pyloric 

 strainer or from this to the intestine and liver. 



Aside from the grinding mechanism, the most essential parts of the stomach, 

 according to Williams, are the distributing and circulating canals (the upper and lower 

 cardiac and the lower pyloric canals) and the five food gates or valves, namely, the 

 cardio-pyloric valve between the two main divisions of the stomach and the four 

 pyloric valves which guard the passage of food to the intestine and the Uver. There 

 is a small intestinal caecum, which extends forward over the dorsal wall of the stomach, 

 and the short duct of the liver or gastric gland opens into the intestine between the 

 ventral and lateral pyloric valves on either side. The conspicuous horn-shaped proc- 

 esses at the base of the pyloric sac and in front of the intestinal caecum are the lateral 

 pyloric pouches, where the finer particles of food are sifted out for delivery to the liver. 

 In addition to the canals mentioned there are also a pair which traverse the median 

 section of the pyloric sac. A small rudimentary tooth (infero-lateral tooth) is seen 

 projecting from between folds of the stomach wall immediately below the anterior end 

 of the lateral tooth, on either side (pi. xxxiii). 



Upon each side of the stomach sac, at its forward end, a large ovate plate (pi. 

 xxxiii) is to be seen, called the gastrolithic plate (lying immediately above a small 

 gastrolithic bar). This plate is composed of a modified epithelium, which between the 

 molts secretes the rounded mass of snow-white prisms known as the stomach stones or 

 gastroliths. Williams has found that the gastroUths make their first appearance in the 

 fourth stage, when for the first time the skeleton abounds in lime. 



Over thirty distinct plates, ossicles, and bars enter into the complex framework 

 of this organ, governed by some fourteen pairs of intrinsic and extrinsic muscles, some 

 of these serving to suspend the sac to the dorsal wall of the carapace (such as the 

 anterior, posterior, and lateral gastric muscles), for "turning the wheels" of the gastric 

 mill and feeding the "hopper," as well as for dilating or constricting the cardiac and 

 pyloric chambers. 



From the mouth the food passes into the short esophagus, through an esophageal 

 valve, and into the cardiac chamber of the stomach sac. Thence it is delivered through 



