AND ON THE LAWS OF ITS FUNCTION. 303 



ture : 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 development. At first they 

 are mere primitive nucleated cells ; further on they contain young cells ; and be- 

 yond this they assume the characters of primary secreting cells, being distended 

 with yellow bile, in which float oil globules, the oil in some instances occupying 

 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 : 



1st, Each follicle is virtually permanent, but actually in a constant state of 

 development and growth. 



2d, This growth is contemporaneous with the function of the gland, that func- 

 tion 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. 



th, The vital action of some follicles is continuous, the germinal spot in eactj 

 never ceasing to develope nucleated cells, which take on the action of, and become 

 primary secreting cells, as they advance along the follicle. The action of other 

 follicles is periodical. 



5th, I have not been able to satisfy myself, but I am inclined to believe, that 

 the wall of the follicle is also in a state of progressive growth, acquiring additions 

 to its length at its blind extremity, and becoming absorbed at its attached extre- 

 mity.* A progressive growth of this kind would account for the steady advance of 

 its attached contents, and would also place the wall of the follicle in the same 

 category with the primary vesicle or wall of the acinus in the vesicular glands. 



6th, The primary secreting cells of the follicle are not always isolated. They 

 are sometimes arranged in groups, and when they are so, each group is enclosed 

 within its parent cell, the group of cells advancing in developement according to 

 its position in the follicle, but never exceeding a particular size in each follicle. 



I am inclined to believe, although of this I have not satisfied myself, that, 

 there is an order of glands, namely, those with very much elongated and anasto- 

 mosing ducts, which do not possess germinal spots in particular situations, but in 

 which these spots are diffused more uniformly over the whole internal surface of 

 the ducts. I am the more inclined to believe this, from v/hat I have observed in 



* Mr Henry Goodsir, in a paper on the Development and Metamorphoses of Caligus, read in the 

 Wernerian Society, April 1842, has stated that the wall of the elongated and convoluted follicle, which 

 constitutes the ovary in that genus, grows from its blind to its free extremity, at the same rate as the 

 eggs advance in development and position. 



VOL. XV. PART II. 4 N 



