250 
bulletin of the bureau of fisheries. 
The stomach is divided into a larger forward, or cardiac division, for storage chiefly, 
and a smaller hinder, or pyloric section (pi. xxxm 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 liquids 
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 liver. 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. xxxm). 
Upon each side of the stomach sac, at its forward end, a large ovate plate (pi. 
xxxm) 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 gastroliths 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 
