190 



COMPARATIVE ANATOMY 



CHAP. 



the oesophagus of the Octopoda, however, is provided with a lateral pouch, the crop 

 (Fig. 127, p. 147), whose walls are not glandular. This may 

 serve as a reservoir of food when the stomach is already 

 full. In Nautilus, the crop is a very large saccular widening 

 of the oesophagus, larger than the stomach itself. 



5 



9 \- 



13 



FIG. 162. Diagram of the 

 anatomy of Clio striata, 

 from the right side ; the 

 heart, kidney, and mantle of 

 this side removed (after 

 Pelseneer). 1, Fin (parapo- 

 dium); 2, aperture of the 

 penis ; 3, right tentacle ; 4, 

 genital aperture ; 5, penis ;. 

 6, oesophagus ; 7, dental 

 plates of the stomach ; 8, 

 ducts of the gonad ; 9, gonad ; 

 10, intestine ; 11, digestive 

 gland ; 12, ducts of the same 

 (cut off) ; 13, accessory 

 glands of the genital appar- 

 atus ; 14, mantle cavity ; 15, 

 terminal portion of the geni- 

 tal ducts ; 16, central ner- 

 vous system (ganglion ring); 

 17, foot ; 18, pharynx. 



D. The Mid-gut with the Stomach and 

 Digestive Gland (Liver). 



The oesophagus leads into a wider portion of 

 the alimentary canal, the stomach. Into this the 

 ducts of a gland open ; this gland is strongly 

 developed in nearly all Molluscs, and is usually 

 called the liver, but may be more appropriately 

 named the digestive gland, since it in no way 

 fulfils the functions of the vertebrate liver. As 

 far as is at present known, it functions rather as 

 a pancreas, or it combines the functions of the 

 various digestive glands of the vertebrate intes- 

 tine, no such thorough division of labour as is 

 found in the Vertebrates having taken place. The 

 digestive gland is, in most cases, a richly-branched 

 tubular or acinose gland, which to the naked eye 

 appears a compact lobate body of a brown, 

 brownish-yellow, or reddish colour. Its glandular 

 epithelium consists of three sorts of cells 

 hepatic, ferment, and calcareous cells. In 

 many Nudibranchia the gland breaks up into 

 branching intestinal diverticula, which spread 

 through the body almost like the gastro-canals or 

 intestinal branches in the Turbellaria, and run up 

 into the dorsal appendages of the body (clado- 

 hepatic Nudibrancliia). 



Choetoderma, among the Solenogastres, has a 

 simple midgut diverticulum, which may corre- 

 spond morphologically with the digestive gland 

 of other Molluscs ; but in Proneomenia, Neomenia, 

 etc., the straight mid-gut is provided throughout 

 its whole length with narrow lateral glandular 

 sacs arranged closely one behind the other at 

 right angles to it. 



A part of the mid - gut gland (the part 

 nearest to the point where the duct leaves it) 

 and the glandular epithelium of the duct may be 

 specially differentiated in Cephalopoda, and may, 

 finally, form a distinct system of glands called the 

 pancreas (Fig. 160). 



