SECRETION. 



331 



whatever secondary arrangement there may be, all have the same essen- 

 tial character of rounded groups of vesicles containing gland-cells, and 

 opening by a common central cavity into minute ducts, which ducts in 

 the large glands converge and unite to form larger and larger branches, 

 and at length by one common trunk, open on a free surface of membrane. 

 Among these varieties of structure, all the secreting glands are alike 

 in some essential points, besides those which they have in common with 



FIG. 227. -Plans of extension of secreting membrane by inversion or recession in form of cavi- 

 ties. A, simple glands, viz. q, straight tube ; 7i, sac; i, coiled tube. B, multilocular crypts; k, of 

 tubular form; I, saccular. C. racemose, or saccular compound gland; m, entire gland, showing 

 branched duct and lobular structure; n, a lobule, detached with o, branch of duct proceeding from 

 it. D, compound tubular gland (Sharpey). 



all truly secreting structures. They agree in presenting a large extent 

 of secreting surface within a comparatively small space; in the circum- 

 stance that while one end of the gland-duct opens on a free surface, the 

 opposite end is always closed, having no direct communication with 

 blood-vessels, or any other canal; and in a uniform arrangement of ca- 



