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, 

 cs ; 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). 



Fig. 6. — Astaeiis fliiviatilis. — 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 ; eg, cervical 

 groove ; cce, csecum ; epv, cardio-pyloric valve ; cs, cardiac portion 

 of stomach; the circular area immediately below the end of the 

 line from ei marks the position of the gastrolith of the left 

 side; hg, hind-gut; lb, labrum; It, lateral tooth of stomach; 

 m, mouth ; mg, mid-gut ; mt, median tooth ; ce, oesophagus ; pc, pro- 

 cephalic process ; ^.posterior gastric muscle ; ps, pyloric portion of 

 stomach ; r, 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 



