451 



SECRETION. 



4th, Cells larger than the last, assuming more constant state of change, passing through 

 of a globular form, still closed, full of nu- stages of development, maturity, and atrophy. 



" 2d. The state of change is contempo- 

 raneous with, and proportional to, the forma- 

 tion of the secretion, being rapid when the 

 latter is profuse, and vice versa. 



" 3d. The acinus is at first a single nu- 

 cleated cell. From the nucleus of this cell 

 others are produced. The parent-cell, how- 

 ever, does not dissolve away, but remains as 

 a covering to the whole mass, and is ap- 

 pended to the extremity of the duct. Its 

 cavity, therefore, as a consequence of its mode 

 of development, has no communication with 

 the duct. The original parent-cell 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. 



" 4. The secretion of a gland is not the 

 product of the parent-cell of the acinus, but 

 of its included mass of cells." * 



An ideal representation of these successive 

 changes is given mfig. 322. At b is seen a 



Progressive development of vesicles oftestisof Squalus 

 cornubicus. 



a, portion of duct with a few nucleated cells, the 

 primary or germinal cells of the future acini, at- 

 tached to its walls ; b, c, d, e, f, primary cells, or 

 acini, in successive stages ; g, one of the secondary 

 cells in an immature state ; h, a secondary cell 

 elongated into a cylinder, each cell of its com- 

 posite nucleus elongated into a spiral ; i, k, the 

 spiral cells or spermatozoa free. (After Goodsir.) 



cleated cells, and situated more towards the 

 surface of the lobe (c). 5th, The full sized 

 vesicles situated at the surface of the lobe, 

 with their contents in various stages of deve- 

 lopment (d, e, /). These vesicles are spheri- 

 cal and perfectly closed ; that part of the 

 wall of each, which is attached to the hollow 

 pedicle, forming a diaphragm across the pas- 

 sage, so that the vesicle has no communica- 

 tion with the ducts of the gland. The con- 

 tained cells are at first spherical (g) ; but as 

 the spermatozoa are gradually formed within 

 them, they present a cylindrical form (A), 

 and they are arranged within the vesicles in 

 somewhat of a spiral manner (/). When the 

 development has advanced to this stage, the 

 diaphragms across the necks of the vesicles 

 dissolve away or burst ; and the bundles of 

 spermatozoa float along the ducts of the 

 gland, some of them separating into indivi- 

 dual filaments (i, k). Besides the bodies 

 now described, Prof. Goodsir has observed 

 what he considers to be vesicles which have 

 discharged their contents, and which are in a 

 state of atrophy (fg. 322. a). 



The testis of Squalus cornubicus, the func- 

 tional history of which has been now given, 

 is considered by Prof. Goodsir as a type of a 

 number of glands, whose action takes place 

 after the same manner ; and he lays down the 

 following general facts, which he has ascer- 

 tained in regard to glands of this order. 



" 1st, The glandular parenchyma is in a 



Fig. 322. 



Ideal representation of changes occurring in vesicular 

 glands. 



a, a bunch of acini in various states of development, 

 maturity, and atrophy ; b, c, d, are diagrams, ar- 

 ranged so as to illustrate the intimate nature of 

 the changes which occur in vesicular glands when 

 in a state of functional activity. (After Goodsir.) 



portion of gland with two acini ; one of them 

 being a simple primary cell, the other being 

 in a state of development, its nucleus pro- 

 ducing young cells. At c, both acini are ad- 

 vancing ; the second has almost reached ma- 

 turity. At d the second acinus is ready to 

 pour out its contents, and the first to take its 

 place ; and at e, the second acinus is thrown 

 in a state of atrophy, whilst the first is be- 

 come fully matured. 



There is another set of glands, in which the 

 follicles remain persistent for a much longer 

 period,' and continue to produce many suc- 

 cessive generations of secreting cells ; of these, 

 the liver of the Crustacea may be taken as 

 the type. From the appearances presented 

 by these follicles, which have been already 

 figured and detailed (fg. 312.), it seems fair to 

 conclude, that the development of these cells 



* Anatomical and Pathological Observations, 

 p. 30. 



