THE EPITHELIAL TISSUES. 



61 



tion of the gland is discharged upon some free surface through a 

 tubular outlet, called the duct. This is frequently lined with a non- 

 secreting layer of epithelial cells differing in character from the 

 actively secreting epithelium in the deeper portions of tire glandular 

 passages (Figs. 42-47). 



Fig. 42. 



Fig. 43. 



Fin. 44. 



Fig. 45. 



Diagrams representing various types of gland. 



Fig. 42.— Simple tubular gland : a, epithelium covering the surface on which the secretion is 

 discharged; b, mouth of gland; c, epithelium lining the duct. This gradually passes 

 into the secreting epithelium. Some simple tubular glands have no such distinction 

 between the cells near the mouth and those nearer the fundus, but all the cells are of the 

 secreting variety — i.e., exercise that function, e, secretory epithelium ; d, lumen. The 

 sweat-glands are simple tubular glands which are coiled in their lower part to form a 

 globular mass. 



Fig. 43. — Compound tubular gland : /, duct ; g, acinus. 



Fig. 44.— Racemose tubular gland : /,/,/, ducts ; g, g, acini. 



Fig. 45.— Simple saccular gland : /, duct ; g, acinus. 



