300 



ESSENTIAL STRUCTURE OF SECRETING ORGANS. 



(fig. 164) j and thus the entire mass may be composed of 

 numerous lobules, each having its own duct. Passing to still 

 higher forms, we find all the ducts coalescing into a common 

 trunk, so that the gland bears a strong resemblance to a bunch 

 of grapes ; as is seen in fig. 1 65, which represents the structure 



Fig. 165. INTIMATE STRUCTURE OF A COMPOSITE GLAND (THE PAROTID). 



of the Parotid (one of the salivary glands) of Man. The 

 main stalk is the duct into which all the others enter ; from 

 this pass off several branches, and these again give off smaller 



twigs, the extremities of which 

 enter the minute follicles in 

 which the secretion is formed. 

 These follicles are lined, as in 

 their simple condition, with cells, 

 which are the essential instru- 

 ments in the production of the 

 secretion; the fluid which they 

 separate is poured, by the 

 giving-way of their walls, into 

 the small canals proceeding 

 from the follicles, thence into 

 the larger branches, and finally 

 into the main trunk, by 

 into the 

 is to be 



employed or from which it is to pass out. The Liver will 

 be seen to possess a structure exactly resembling this, in the 



Fig. 166. PORTION OF ONE OF THE 

 TUBI;LI URINIFERI OF THE 

 HUMAN KIDNEY; 



Showing its lining of flattened epithe- which it is Carried 



Uum ceils. situation where it 



