I9I3-] Ekendranath Ghosh Mollusca, I. 217 



are oval or spherical, and are placed on one side of the cells. The 

 cells open into ver}^ minute salivary ducts which are generally 

 placed in the centre of the lobules. In each lobule a duct begins 

 from the elongated neck of a cell or a group of cells (generally 

 mucous in nature), and then runs for a short distance receiving in 

 its course the secretion of other cells which open into it. The duct 

 in this portion of its course is bounded by the cells themselves, 

 there being no other wall of its own. Several ducts converge from 

 the outer portions of the lobule towards the centre, where they 

 unite to form a lobular duct. The outer portions of the primary 

 ducts and the beginnings of the lobular ducts have their walls con- 

 sisting of a single layer of elongated cells with fusiform or trian- 

 gular nuclei. Then the cells lining their lumen become more or 

 less columnar in shape. At the point of union of these ducts 

 may be seen mucous cells opening directly into them by long 

 narrow necks. 



The oesophagus is a stout tube (a little narrower than the 

 pharynx) which arises from the posterior end of the pharynx in 

 the middorsal line. In the specimen with protruded proboscis, 

 the oesophagus formed a straight tube, extending from behind the 

 pharynx, through the aperture behind the cerebral ganglia, to the 

 anterior end of the midgut gland on the ventral aspect. In the 

 specimen with retracted proboscis, the oesophagus after its origin 

 curves downwards to the left along the groove in front of the radular 

 sac at the ventral aspect. It then passes a little forwards, and 

 bending sharply backwards runs along the midventral line to end 

 in the midgut gland. The oesophagus passes along the ventral 

 surface of the midgut gland for a short distance and then enters 

 into the substance of the gland and ends in the intestine. From 

 the hinder end of the oesophagus at its junction with the intestine, 

 it gives off a short tube which widens out and becomes continuous 

 with the cavity of the midgut gland. 



The digestive or midgut gland (liver) is a large elongated 

 conical body, extending over the posterior three- fourths of the 

 cavity of the body. Anteriorh' it is truncated obliquel}" and forms 

 a concave surface directed downwards, forwards and to the left. 

 Posteriorly it is tapering, and is connected to the posterior end of 

 the body b}^ a strand of connective tissue. The surface of the 

 gland is finely lobulated. The cavity of the gland is narrow, with 

 numerous fine slit-like branches projecting into the substance of the 

 wall of the gland. The cavity becomes still narrower and irregular 

 towards the posterior end of the gland. 



Minute struchire. — The gland consists of numerous extremely 

 elongated glandular cells, which are arranged side by side upon a 

 thin layer of connective tissue which projects inwards from all 

 sides towards the cavity of the gland. At the outer side this layer 

 is continuous with the thin sheath of the gland. Each cell con- 

 sists of granular protoplasm, and contains an elongated nucleus to- 

 wards its attached end. Amongst these cells are found goblet 



