SECRETING STRUCTURES. 423 



again, others rise in the same manner. The parent cell, 

 however, does not dissolve away, but remains as a covering to 

 the whole mass, and is appended to the extremity of the duct. 

 Its cavity, therefore, as a consequence of its mode of develop- 

 ment, has no communication with the duct. 



The original parent cell now begins to dissolve away, or 

 to burst into the duct at a period when its contents have 

 attained their full maturity. This period varies in different 

 glands, according to a law or laws peculiar to each of them. 



6th, In the gland there are a number of points from which 

 acini are developed, as from so many centres. These I name 

 the germinal spots of the gland. 



7th, 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. 



8th, There are three orders of secretions : (1.) A true secre- 

 tion that is, matter formed in the primary secreting cell- 

 cavities ; or, (2.) A mixture of a fluid formed in these cell- 

 cavities with the developed or undeveloped nuclei of the cells 

 themselves ; and, (3.) 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 ex- 

 tremity downwards, these cells appear in progressive states of 

 development. 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 dis- 

 tended with yellow bile, in which float oil-globules, the oil in 



