VII 



MOLLUSCA—THE ALIMENTARY CANAL 



195 



unpaired in the adult. The whole of the much hranohed gland is surrounded by a 

 common integument, and it thus outwardly appears to be compact. 



The digestive gland of Nautilus consists of five lobes (four paired and one 

 unpaired), which lie around the crop. They have two ducts, which enter the crecum 

 through a short common terminal portion. 



In the Dibranchia also, the digestive gland always lies on the ventral side of the 

 stomach, close to the ascending oesophagus. 

 It is undivided, and round or oviform in the 

 Octopoda, Oegopsidce, and Sepiola. In Lolicjo 

 and Scpioteuthis, it is traversed by the oeso- 

 phagus and the aorta ; in Enoploteuthis, its 

 dorsal half is cut into two points by these 

 organs ; and the same is the case in Eossia. 

 In Sepia and Spirula, the gland forms two 

 lateral lobes which are distinct in Sepia, but 

 connected along the middle line in Spirula. 



There are always two ducts (gall ducts) 

 which rise near the median plane fi'om the 

 upper part of the gland, and open into the 

 stomachal coeoum separately or through a 

 common terminal portion. 



The following facts have been ascertained 

 as to the function of the so-called pancreas 

 of the Cephalopoda. It is originally a 

 specially differentiated portion of the diges- 

 tive gland, and is easily distinguishable in 

 the Octopoda by its different colour ; it lies 

 near that part of the gland from which the 

 ducts spring. In Loligo, the pancreas is 

 found in the much thickened wall of the 

 ducts themselves. In this case it consists 

 of numerous glandular anastomosing out- 

 growtlis of the epitheliiun of the ducts into 

 their wall. In other Decapoda, these gland- 

 ular outgrowths pass from the wall of the 

 ducts into the surrounding body cavity, and 

 then each duct appears throughout its whole 

 length to be covered with acinose or ramified 

 "pancreatic appendages." The pancreatic pylorus; 8. 



secretion contains diastase, and appears to ™ t^"^ ^ ^ ^^ ■ j. j.-^ , ■ , 



, » , p . . „ . , bag ; 7, aperture of the same into the hind- 



carry out only one part of the functions of the ^^^ 



digestive gland, viz. that part which corre- 

 sponds with the digestive functions of the salivary glands in the higher Vertebrates. 

 The small intestine, in which among all Molluscs the resorption of the digested 

 food chiefly (if not exclusively) takes place, is short in the carnivorous Cephalopoda, 

 and foi-ms several coils only in Tremoetopus violaceiis. 



Fig. 166. ^ Alimentary canal of Loligo 

 sagittata (without pharynx and salivary 

 glands) partly cut open (after Gegenbauer). 

 1, Oesophagus ; 2, probe, inserted into the 

 stomach ; 4, stomachal coBCum 

 with spiral coeeum 5 ; 6, hind-gut ; S, ink- 



E. Hind-gut (Reetum). 



This is generally short in Molluscs. Where it is sharply marked 

 off from the small intestine, it usually differs from the latter in being 

 thicker and more muscular. 



