THE “ CRABS’-EYES.” 29 
middle region of that part of the carapace which lies 
behind the cervical groove; or, in other words, in the 
dorsal region of the thorax. In front of it, and therefore 
in the head, is a large rounded sac, the stomach (fig. 5, 
es; fig. 6, cs, ps), from which a very delicate intestine 
(figs. 5 and 6, hg) passes straight back through the thorax 
and abdomen to the vent (fig. 6, a). 
Fic. 6.——Astacus fluriatilis.—A longitudinal vertical section of the ali- 
mentary canal, with the outline of the body (nat. size) :—a, vent; ag, 
anterior gastric muscle ; bd, entrance of left bile duct ; cg, cervical 
groove; c@, cecum; cpr, cardio-pyloric valve ; ¢s, cardiac portion 
of stomach ; the circular area immediately below the end of the 
line from es marks the position of the gastrolith of the left 
side; hg, hind-gut; 7b, labrum; /¢, lateral tooth of stomach; 
m, mouth ; mg, mid-gut ; mt, median tooth; @, cesophagus ; pe, pro- 
cephalic process ; yg, posterior gastric muscle ; ys, pyloric portion of 
stomach; *, annular ridge, marking the commencement of the 
hind-gut. 
In summer, there are commonly to be found at the sides 
of the stomach two lenticular calcareous masses, which 
are known as ‘‘ crabs’-eyes,” or gastroliths, and were, in 
old times, valued in medicine as sovereign remedies for all 
sorts of disorders. These bodies (fig. 7) are smooth and 
flattened, or concave, on the side which is turned towards 
