30 SECRETING STRUCTURES, 



1th, The secretion of a gland is not the product of the parent 

 cell of the acinus, but of its included mass of cells. The parent 

 cell or vesicle may be denominated the primary cell ; its included 

 nucleated cells, after they have become primary secreting cells, 

 may be named secondary cells of the acinus. 



Sth, There are three orders of secretions, 1st, A true secretion, 

 that is, matter formed in the primary secreting cell cavities ; 

 or, 2d, A mixture of a fluid formed in these cell cavities with the 

 developed or undeveloped nuclei of the cells themselves ; and, 3c?, 

 It may be a number of secondary cells passing out entire. 



In the liver of Carcinus Mcenas, and other Crustacea, it 

 may be observed, that each of the follicles of which it consists 

 presents the following structure. The blind extremity of the 

 follicle is slightly pointed, and contains in its interior a mass of 

 perfectly transparent nucleated cells. From the blind extremity 

 downwards, these cells appear in progressive states of develope- 

 ment. At first they are mere primitive nucleated cells ; further 

 on they contain young cells ; and beyond this they assume the 

 characters of primary secreting cells, being distended with yellow 

 bile, in which float oil globules, the oil in some instances occupy- 

 ing the whole cell. Near the attached extremity of the follicle 

 an irregular passage exists in the midst of the cells, and allows 

 the contents of the cells which bound it to pass on to the branches 

 of the hepatic duct. 



This arrangement of the secreting apparatus may be taken as 

 the type of an order of glands, which consist of follicles more or 

 less elongated. Growth in glands of this kind is regulated by 

 the following laws : 



\stj Each follicle is virtually permanent, but actually in a con- 

 stant state of developement and growth. 



2d, This growth is contemporaneous with the function of the 

 gland, that function being merely a part of the growth, and a 

 consequence of the circumstances under which it occurs. 



3d, Each follicle possesses a germinal spot situated at its blind 

 extremity. 



4/i, The vital action of some follicles is continuous, the ger- 

 minal spot in each, never ceasing to develope nucleated cells, 



