ALIMENTARY CANAL OF MOLLUSCA. 



363 



mid-gufc, whicli is provided with, a caecum ; this 

 iuner wall thrown into longitudinal folds for 

 the first part of its length. It generally takes 

 a straight course (it is slightly coiled in 

 Nautilus and the Octopoda only) forwards, 

 to a short hind-gut (Fig. 193, i), which opens 

 to the exterior at the base of the funnel. In 

 many Cephalopoda there are two or three 

 valves or valvular processes around the anus, 

 the muscles in which are remarkably well 

 developed. 



The ca3ca (Fig. 193, c) at the commence- 

 ment of the mid-gut vary not only in external 

 form, but also in the characters of their in- 

 ternal surface. The cascum is either rounded 

 (Nautilus, Rossia, Loligopsis) 



it is often 



When the 



portion also has its 



in the latter case 

 (Sepia, Octopus), 

 long, it is often 

 The inner surface 

 are 



cesses, which 



or elongated ; 

 spirally coiled 

 ca3cum is very 

 coiled several times (e e). 

 is either thrown into pro- 

 arranged in a lamellar 

 fashion (Nautilus), or these processes may 

 form circular folds arranged in conformation 

 with the spiral form of the cajcum. Two of 

 the largest folds receive the efferent ducts of 

 the liver, and project so far into the lumen of 

 the enteron as to form at times a valve-like 

 apparatus which shuts off the caecum. It is 

 probable that this caecum has a secretory 

 function, as in those forms (Loligo vulgaris) 

 in which the folds are absent a large number 

 found in its walls. 



Fig. 193. Digestive appa- 

 ratus of Loligo sagit- 

 tata. oe CEsophagus. 

 v The stomach, opened 

 longitudinally. a> A 

 probe passed through 

 pylorus, c Commence- 

 ment of the caecum. 

 e e Its spiral portion. 

 i Hind-gut. a Ink-bag. 

 b Its opening iuto the 

 rectum (after Home). 



of glands are to be 



Organs appended to the Enteric Canal. 



1) Appendages of the fore-gut. 



§ 280. 



Of those glandular organs which are connected with the enteric 

 caual, the salivary are found only in those forms in which the 

 pharynx is developed ; it is possible therefore to make out a certain 

 connection between these structures. In the Gastropoda they are 

 always placed on each side of the fore-gut, and open into the 

 pharynx. Sometimes they form short cascal tubes (Pteropoda), 

 which are sometimes hidden in the very substance of the pharynx 



