80 THE NATURAL HISTORY OF THE COMMON CRAYFISH. 
the cavity of the stomach; while the opposite side, being 
convex and rough with irregular prominences, is some- 
thing like a “ brain-stone ” coral. 
Moreover, when the stomach is laid open, three large 
Fig. 7.—Astacus fluviatilis.—A gastrolith ; A, from above ; B, from 
below ; C, from one side (all x 5); D, in vertical section (x 20). 
reddish teeth are seen to project conspicuously into its 
interior (fig. 6, It, mt); so that, in addition to its six 
pairs of jaws, the crayfish has a supplementary crushing 
mill in its stomach. On each side of the stomach, there 
is a soft yellow or brown mass, commonly known as the 
