406 SECRETION. 



secreting apparatus, namely epithelium, simple membrane, 

 and blood-vessels, having been already described in 

 this and previous chapters, we may proceed to consider 

 the manner in which they are arranged to form the 

 varieties of secreting glands. 



SECRETING GLANDS. 



The secreting glands are the organs to which the office 

 of secreting is more especially ascribed : for they appear to 

 be occupied with it alone. They all present, amid manifold 

 diversities of form and composition, a general plan of 

 structure, by which they are distinguished from all other 

 textures of the body; especially, all contain, and appear 

 constructed with particular regard to, the arrangement of 

 the cells, which, as already expressed, both line their tubes 

 or cavities as an epithelium, and elaborate, as secreting 

 cells, the substances to be discharged from them. 



For convenience of description, they may be divided into 

 three principal groups, the characters of each of which are 

 determined by the different modes in which the sacculi or 

 tubes containing the secreting cells are grouped : 



i. The simple tubule, or tubular gland (A, fig. 101), examples 

 of which are furnished by the several tubular follicles in 

 mucous membranes : especially by the follicles of Lieber- 

 kuhn in the mucous membrane of the intestinal canal 

 (p. 306), and the tubular or gastric glands of the stomach 

 (p. 275). These appear to be simple tubular depressions of 

 the mucous membrane on which they open, each consisting 

 of an elongated gland- vesicle, the wall of which is formed 

 of primary membrane, and is lined with secreting cells 

 arranged as an epithelium. To the same class may be 

 referred the elongated and tortuous sudoriparous glands of 

 the skin (p. 428), and the Meiboinian follicles beneath the 

 palpebral conjectiva; though the latter are made more 

 complex by the presence of small pouches along their sides, 

 (B, fig. 101), and form a connecting link between the 



