204 



THE CRAYFISH. PHYLUM ARTHROPODA 



into the large proventriculus, often called the stomach (Fig. 137). 

 This consists of two chambers, a large forepart or mill-chamber, 



.t.ear. •P''"-- 

 1 u, ca r. , car. 



B 



-^.c. 



-iOes. 



U£ar. 



fiar. Q 



Fig. 137. — The proventriculus ot the crayfish. 



A The whole organ from above ; B, the same from the right side ; C, the left half from within, the muscles 

 being relaxed ; £>, the ossicles of the mill in median section, the anterior and posterior gastric muscles 

 being contracted ; £, the mill in plan. All the figures are semi-diagrammatic, much detail being 

 omitted. 



bri.. Bristles for filtering ; car., cardiac ossicle ; cm., caecum ; j.c, pyloric or filter-chamber ; gUh., position 

 of gastroUth ; h.g., hind-gut ; l.p., lateral pouch ; l.t., lateral tooth ; m.c, mill-chamber ; m.g., mid- 

 gut ; m.t., median tooth ; o.h., opening of bile duct ; as., oesophagus ; p. car., pterocardiac ossicle; 

 p.py., prepyloric ossicle ; py., pyloric ossicle ; u.car., urocardiac ossicle ; v., the several pieces of an 

 arrangement of valves which directs the solid residue of the food into the hind-gut, there to become 

 the faeces ; z.car., zygocardiac ossicle. 



often known as the cardiac division of the stomach, and a smaller 

 hind part or filter-chamber, often known as the pyloric division 

 of the stomach, separated from the mill-chamber by a pit in 

 the roof. From the filter-chamber the short mid-gut or mesenteron 

 leads backwards to the long hind-gut, sometimes called the 

 ' intestine'. The epidermis and cuticle turn inwards at the mouth 

 and line the gullet and proventriculus, which are together known 

 as the fore-gut. The mid-gut is lined with soft endoderm, and the 

 hind-gut is again lined with epidermis and cuticle. The cuticle 

 in the gut is for the most part thin, but in places in the 



