41 



tract. Underlying the epithelium is a thin but distinct 

 basal membrane, and below this a layer of connective 

 tissue with muscle fibres. 



Numerous large blood spaces occur in the connective 

 tissue, so that it may practically be said that the stomach 

 lies in a blood cavity. 



The conspicuous grooves, which have already been 

 referred to as occurring on the inner surface of the 

 stomach, are produced by variations in height of the 

 epithelial cells. In this respect the epithelium agrees 

 with the same layer in the stomach of the lamellibranch 

 Pecten. 



The Digestive Gland. — This large gland has been 

 known as the liver, the Hepatopancreas, and the Gastric 

 Gland. It is now regarded as a " pancreas," but with 

 additional functions, such as storing pigment and fat. 

 The term liver should certainly be abolished and replaced 

 by the name " digestive gland." 



The gland is tubular, and is formed by repeated 

 division of the ducts which open from the stomach. 

 These numerous branches ramify still further, and even- 

 tually end blindly as caeca. The gland, like that of 

 Pecten, is composed almost entirely of these caeca and 

 ductules, and the connective tissue which encloses each 

 ductule and caecum, and is therefore to be seen between 

 them, is reduced to a minimum. There are numerous 

 blood lacunae penetrating between the caeca. 



The appearance of stained sections is very character- 

 istic, for almost all the gland cells are crowded with 

 large, oily-looking granules, which stain vividly with 

 eosin (fig. 29, Dg. gr.). They are so numerous, in fact, 

 that details of cell structure are almost entirely obscured. 

 Commencing from the opening of a ductule into the 

 stomach, and passing towards the blind end of one of its 



