ENTr-:RIC CANAL 



357 



spoken of as the stomach, 

 which occupies a great part of 

 the interior of the head, and 

 is divided into a large ante- 

 rior division (o), and a smaller 

 posterior division {ps) : the 

 latter passes into the intestine, 

 which consists of a narrow 

 and very short mid-gut {iiid) 

 from which a somewhat wider 

 hind-gut (Jid) extends to the 

 anus {an), situated on the 

 ventral surface of the telson. 



The outer layer of the en- 

 teric canal consists of connec- 

 tive tissue containing striped 

 muscular fibres : within this is 

 a single layer of columnar 

 epithelial cells, none of them 

 glandular. In the gullet and 

 gizzard and in the hind-gut 

 the epithelium secretes a layer 

 of chitin, which thus consti- 

 tutes the innermost layer of 

 those cavities. It is proved 

 by development that the mid- 

 gut, which has no chitinous 

 lining, is the only part of the 

 enteric canal developed from 



e/j.. / '- 



A 



en.^ 



en..3~ 



ccrt.-> 



^exi- 



art. wi 



-- ea^ 



l~e?1^.Z 



Fig. 85. — A leg of the Fresh-water Cray- 

 fish with part of the exoskeleton 

 removed to show the muscles. 

 en. 2 — en. 5, segments of endopodite ; /;. hinges ; art. in. articular membrane ; cxt. 

 extensor muscle ; _/?. flexor muscle. (From Parker andHaswell's Zoology.) 



A A 3* 



