ENTERIC 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 (a), and a smaller gj^ 

 posterior division {ps) : the 

 latter passes into the intestine, 

 which consists of a narrow 

 and very short mid-gut {md) 

 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 



A- 



en.-f- 



en:3' 



art. 7 



CPT^.S' 



exZ- 



art.m. 



exi 



—en- <2 



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

 fish with part of the exoskeleton 

 removed to show the muscles. 

 in. 2— £?«. 5, segments of endopodite ; //. hinges ; art.m. articular membrane ; c.xt. 

 e.xtensor muscle ; yf. fle.xor muscle. ( From Parker and Haswell's Zoology.) 



A A 2* 



