Royal Society. 275 



duct becomes very minute and gradually loses all definite structure, 

 appearing at last like a mere tract of granular matter ; in either 

 case there is no communication by continuity with the surrounding 

 parenchyma. Large yellow corpuscles, peculiar cells, and a consi- 

 derable quantity of free oily matter usually existing in the liver of 

 various fishes, seem generally to indicate a great superiority in the 

 amount of secretory over that of excretory action, and to betoken 

 clearly the feeble intensity of the aerating function. 



In Reptiles, there is the same arrangement in the liver, namely, 

 a secreting parenchyma of cells and an apparatus of excretory ducts, 

 which have the same essential characters as those of fishes; but 

 there exists very frequently in the parenchyma remarkable dark 

 corpuscles, which appear to be masses of retained biliary matter, 

 the import of which, in the situation they occupy, is doubtless the 

 same as that of the similar masses existing in fishes. 



In Birds, the parenchyma of the liver is remarkably free from oily 

 or retained biliary matters; it often consists almost wholly of free 

 nuclei and granular matter, with scarcely a single perfect cell ; the 

 excretory ducts often greatly resemble those of reptiles, sometimes 

 rather those of mammalia; the essential character is, however, always 

 the same, namely, that they terminate without forming any important 

 connexion with the parenchyma. 



In Mammalia, the parenchyma of the liver consists usually of per- 

 fect cells, which are arranged often in linear series of considerable 

 length, radiating from the axis of each lobule ; these unite at various 

 points with each other, so as to present a more or less decidedly 

 plexiform appearance. Each lobule, as described by Mr. Kiernan, 

 is separated from the adjacent ones by the terminal twigs of the 

 portal vein, and to a greater or less extent by a " fissure," though in 

 most animals the lobules are continuous with each other both above 

 and below the fissure. The elaboration of the secreted product 

 seems to be most completely effected in the cells adjoining the 

 margins of the lobules, which are often seen to contain a larger 

 quantity of biliary matter than those in the interior, and to be appa- 

 rently in the act of discharging it into the fissure; the margin of 

 the lobule then presents an irregular surface with large globules of 

 the secretion clustering together all over it. The capsule of Glisson 

 surrounding the vessels in the portal canals gives a fibrous invest- 

 ment to those surfaces of the lobules which are towards the canal ; 

 but when it has arrived in the fissures, it forms a continuous mem- 

 brane lining the surfaces of opposite lobules ; this membrane is often 

 truly homogeneous, and closely resembles the bast ment tissue : there 

 appears occasionally to be a delicate epithelium on its free surface ; 

 but this, as well as the membrane itself, is often absent, when the 

 margin of the lobules is in that condition which has just been de- 

 scribed and which may be termed active. The minute branches of 

 the hepatic duct as they approach their termination undergo a re- 

 markable alteration in their structure ; they lose their fibrous coat, 

 which blends itself with the membranous expansions of the capsule 

 of Glisson ; their basement membrane becomes gradually indistinct, 



