VII 



MOLLUSCA—THE ALIMENTARY CANAL 



195 



unpaired in the adult. The whole of the much branched 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 pau-ed and one 

 unpaired), which lie around the crop. They have two ducts, which enter the ca;cuni 

 through a short common terminal portion. 



In the Dihranchia 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, Ocgopsidcc, and Sepiola. In LolUjo 

 and Scpiotcutkis, it is traversed by the oeso- 

 phagus and the aorta ; in EnoploteutJiis, its 

 dorsal lialf is cut into two points by these 

 organs ; and the same is the case in Rossia. 

 In Scjna and SpiruJa, 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 from the 

 upper part of the gland, and open into the 

 stomachal ccecum separately or through a 

 common terminal jjortion. 



Tlie 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 anastojnosing out- 

 growths of the epithelium 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 ^I^: ^Z"'- -Alimentary canal of Loligo 

 ,, .11 sagittata (without pliarynx and salivary 

 then each duct appears throughout its whole gi^nds) partly cut opeu (after Gegenbauer). 

 length to be covered with acinose or ramified i, (Esophagus ; 2, probe, inserted into tlie 

 "pancreatic appendages." The pancreatic pylorus; 3, stomach; 4, stomachal ccecum 



secretion contains diastase, and appears to '^'*'^ *1"''^^ '^°^°"'" ^' ^' '""d-gut ; s, ink- 

 , , p , , ,. J ■ n .1 "^S ; "> aperture of the same into the hind- 



carry out only one part oi the functions of tlie „^(. 



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 Crplmlopoda, 

 and forms several coils only in Trcmoctopus violaceus. 



E. Hind-gut (Rectum). 



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

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

 thicker and more muscular. 



