86 COMPARATIVE ANATOMY 



the case of the chaHce-cells of the palate is mucus or slime) is 

 called the secretum, and is stored up in granules in the distal 

 end of the cell between its nucleus and its free border. When 

 secretion takes place, the free wall of the cell bursts, and the 

 secretum is poured out; the cavity which it occupied in the 

 distal end of the cell remains as a hemispherical cup, which, 

 situated as it is on the attenuated inner extremity, gives the 

 whole cell the appearance of a goblet (fig. 14,- E). After 

 secretion, the protoplasm of the cell again enters into activity, 

 and a fresh secretum is produced, to be discharged in due 

 course. The simplest kind of multi-cellular gland is found in 

 the stomach and intestines of the frog and other vertebrate 

 animals. The mucous membrane lining these organs, when 

 examined superficially with a microscope, is seen to be pitted 

 with innumerable minute orifices placed close together. These 

 are the mouths of simple tubular glands, each of which has 

 the form of a shorter or longer tube formed as a finger-like 

 retess in the connective tissue layer or corium underlying 

 the epithelium of the alimentary tract. These tubes, which 

 are longer in the stomach and shorter in the intestine (in this 

 last situation they are known as the crypts of Lieberkiihn), 

 are lined within by an epithelium, which is a continuation 

 of the columnar epithelium lining the cavity of the 

 alimentary tract. At the mouths of the glands the cells are 

 high and columnar, having the same characters as those 

 lining the cavity of the gut. In the next section of the gland, 

 known as the neck, the cells become progressively shorter and 

 more cubical, and in the deeper part of the gland they become 

 larger and polyhedral, and change their character, in that they 

 have contents in the shape of numerous granules, most 

 abundant in the ends turned towards the lumen of the tube. 

 The opposite ends of the cells are formed of ordinary 

 cytoplasm, and the nucleus lies in the borderland between 

 the granular and the protoplasmic part. The granules are the 

 secretum of the cell, and are formed by the activity of its 

 protoplasm. They are, however, not considered to be the 

 actual secretum, but rather a precursor of the secretum 

 peculiar to the cell; and, as the cells of the gastric glands 

 secrete a ferment or enzyme, the granules which are the 

 precursor of that ferment, are called zymogen granules. 

 When secretion takes place the granules are discharged from 



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