EPITHELIUM. 47 



into the basal end of the cell, together with a small mass of 

 protoplasm surrounding it. 



When the cell is filled to the utmost with mucus the outer 

 cell membrane breaks, and through the opening the secretion 

 escapes to the outside, while the cell suffers a considerable reduc- 

 tion in size, and, as it were, collapses. Usually we find goblet 

 cells scattered here and there singly between other cylindrical 

 epithelial cells. They are capable of undergoing many times 

 the changes described, always reassuming their original cylin- 

 drical form, until they finally die or degenerate. 



Goblet cells are distributed widely in the animal organism. 

 Especially do we find them in the epithelium of the respiratory 

 tract (trachea, bronchi) and in the intestinal tract (stomach, 

 small and large intestines). In the mucous glands we find 

 cells containing large quantities of mucus, and representing 

 specific gland cells. 



We now pass on to the true glands, which consist of a few 

 or innumerable gland cells. They form a definite whole which 

 is bound together by connective tissue. The gland cells are 

 arranged beside one another to form a glandular surface, from 

 which the secretion is poured into the gland lumen bounded 

 by such surfaces. The lumen usually is surrounded by many 

 cells ; only exceptionally (liver) is it formed by two cells. 



Often only the deeper lying part of the gland secretes, and 

 is called the gland body, while the parts lying near the outer 

 surface have nothing to do with this activity or play only 

 the subordinate role of conveying the products to the out- 

 side i. e., they form the ducts of the gland. Rarely the duct 

 is absent, and then the gland secretes throughout its whole 

 extent. 



The arrangement of the glandular elements gives to the 

 gland a definite form ; and according to this and to the shape 

 of the lumen we make a morphological classification of glands. 

 They may be in the form of simple cylindrical tubes (tubuli), or 

 in that of spherical or oval sacs (alveoli). These form the tubu- 

 lar and alveolar glands, respectively. We further divide these 

 two groups according as they consist of one or many tubuli or 



