EPITHELIAL GLANDS. 37 



glands the cells here show basal striations, due to rows of granules, which 

 indicate that this portion of the ducts produces a secretion. The terminal 

 part of the ducts of a large gland may be formed of stratified epithelium, 

 perhaps containing mucous cells. The ducts of the liver produce a 

 considerable quantity of mucus, and the bronchi, which from their develop- 

 ment and form may be considered the ducts of the lungs, also contain 

 scattered mucous cells and small secondary mucous glands. Important 

 secretions are elaborated by the efferent and some other ducts of the testis. 

 In the kidney there is no terminal secreting portion as in most glands. 

 The duct-like tubules serve rather to transfer selected materials from the 

 blood to the lumen than to form new substances. This is more obviously 

 true of the alveoli of the lung which merely transmit oxygen and other 

 substances through inert modified cells. Morphologically, that is, in their 

 form and development, both the kidneys and the lungs are glands. 



All epithelial glands arise as outgrowths from an epithelium, as has 

 been described. A few, by the obliteration of their ducts, become separated 

 from their place of origin. This occurs in some small glands associated 

 with the brain and in the thyreoid gland. The closed end pieces of the 

 thyreoid become filled with a secretion that cannot escape. Derived from 

 or in addition to this, there is an internal secretion which is taken up by 

 the vessels adjacent to the basal surfaces of the cells. 



For completely closed epithelial sacs, such as occur in the thyreoid 

 gland and in the ovary, the term follicle is used (Latin, folliculus, "a little 

 bag"). If such closed spaces are pathological or degenerative, they are 

 called cysts. Small round solid masses of lymphoid tissue,* occurring 

 singly or as parts of lymph glands, are called nodules (Latin, nodulus, 

 "a little knot"). Very often and improperly lymph nodules are called 

 follicles. 



In examining sections of glands the student should observe to what 

 class they belong, and should record in case of epithelial glands whether 

 they are unbranched or branched, together with the shape of the end pieces. 

 It is often difficult to determine this shape without resort to reconstructions 

 from a series of sections. The various appearances of the ducts should 

 be studied with the idea of picturing the gland as a whole. 



As a summary of the preceding paragraphs the following tabular 

 classification of glands may be presented : 



I. Epithelial glands, with persistent ducts, producing external secre- 

 tions. 



1. Unicellular glands. 



2. Simple glands. 



a. Ectodermal, e. g., sweat and sebaceous glands. 



