CHAPTER XVIII. 



OF THE SECRETIONS AND EXCRETIONS IN PARTICULAR. 



No exposition of a subject as a whole can attain a sufficient 

 degree of clearness, unless it rests on the description of some 

 particular facts. It is therefore not unsuitable after the general 

 outline, contained in the preceding chapter, to consecrate some 

 pages to the most important and most typical particular secre- 

 tions and excretions. 



Evidently we must place in the first line the hepatic secretion, 

 of all the most complex. In effect, in the liver, the division of 

 labour is far enough from being distinct, and this gland is simul- 

 taneously a closed gland, a secretory gland with excretory 

 conduit, and a gland of excretion. Comparative anatomy, 

 moreover, reveals to us a still higher degree of confusion. In 

 truth, while in diverse vertebrates, for instance, the lizard, the 

 spleen is merely adjoined to the pancreas, in the Chimcera mon- 

 struosa liver, splesn, and pancreas are united into one mass. 



In the mollusks the same epithelial cells seem to be charged 

 to secrete at the same time both sugar and bile ; for this last 

 humour always contains sugar. Besides there is no vena portse, 

 and the saccharo-biliary secretion is accomplished at the expense 

 of the still badly arterialised blood. 



In the superior mammifers the glycogenical cells of the liver 

 are sometimes rounded, sometimes polyhedrical ; their diameter 

 is about 0.02 of a millimetre (Fig. 36). They contain granula- 

 tions and one or two nuclei furnished with nucleoles. These 



