SECRETING STRUCTURES. -)\\ 



never become developed on account of the pressure of the sur- 

 rounding parts, or that they are old vesicles in a state of atrophy 

 after the expulsion of their contents. 



Having now described the changes which are constantly taking 

 place in the testicle of this shark when the organ is in a state of 

 functional activity, I must defer till a future occasion an account 

 of similar changes which occur in the parenchyma of an order of 

 glands, of which the one already described may be considered as 

 a type. I may state, however, that I have ascertained the follow- 

 ing general facts in reference to glands of this order : 



1st, The glandular parenchyma is in a constant state of change, 

 passing through stages of developement, maturity, and atrophy. 



2d, The state of change is contemporaneous with, and propor- 

 tional to, the formation of the secretion, being rapid when the 

 latter is profuse, and vice versa. 



3d, There are not, as has hitherto been supposed, two vital 

 processes going on at the same time in the gland, growth and 

 secretion, but only one, viz., growth. The only difference be- 

 tween this kind of growth and that which occurs in other organs 

 being, that a portion of the product is from the anatomical con- 

 dition of the part thrown out of the system. 



4:th, The vita] formative process which goes on in a gland, is re- 

 gulated by the anatomical laws of other primitive cellular parts. 



5th, An acinus is at first a single nucleated cell. From the 

 nucleus of this cell others are produced. From these, again, 

 others arise 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, there- 

 fore, as a consequence of its mode of developement, has no com- 

 munication 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, ac- 

 cording to a law or laws peculiar to each of them. 



fa/i, 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. 



