REPORT OF COMMISSIONERS OF INLAND FISHERIES. 155 



the stomach or cardiac sac, and a small posterior straining and sort- 

 ing chamber, the pyloric portion of the stomach or pyloricsac. 

 Corresponding to the external constriction, internally there is a 

 grinding apparatus which, in the adult form of the stomach, consists 

 of a median tooth and a pair of lateral teeth. 



The wall of the stomach is formed of four layers of tissue : 



1. An outer layer of connective tissue. This sheet stretches over 

 the irregularities of the stomach and gives the whole exterior a some- 

 what rounded form. In places this outer layer of the stomach is 

 covered by the vascular epithelium (Plate VI, Fig. 9). 



2. A layer of loose connective tissue. This tissue fills up the 

 irregular cavities between the inner and outer contours of the stom- 

 ach wall and contains the blood vessels and intrinsic muscles of the 

 stomach. 



3. The gastric epithelium. This varies in thickness and, cor- 

 respondingly, in the shape of the cells according to the thickness 

 of the chitinous stomach lining. 



4. The chitinous lining of the stomach. This is generally covered 

 with setae of various kinds and in places it is thickened. A deposi- 

 tion of Hme in these thickened areas converts them into "the ossicles" 

 which form the skeleton of the gastric mill. 



The Gastric Ossicles and Muscles. 



In the American lobster the gastric ossicles are essentially like those 

 of the European lobster (Homarus vulgaris) and the crayfish (Astacus 

 fluviatalis), which have been adequately described by Milne Edwards, 

 Oesterlen, Huxley, and T. J. Parker, hence we will omit an extended 

 description of them. We will give generally two names for each 

 ossicle, the shorter names used by Huxley and Parker, and the 

 longer but more descriptive names of Albert. Beginning at the 

 anterior end of the dorsal surface: 



1. The cardiac ossicle or anterior dorsal cardiac plate. This 

 covers nearly the whole of the dorsal surface of the cardiac sac. In 



