AND DEVELOPMENT OF THE LIVER. 
123 
and fill the interstices of the capillary network. Sometimes, as in the Toad and Snake, 
the greater part of the secreting structure is in the form of free nuclei and granular 
matter, with globules of secretion ; in others, as the Tortoise, Frog and Newt, the 
perfect cells are more abundant ; these are usually very delicate, appearing often like 
transparent spaces in the midst of the darker surrounding substance. Besides these, 
the ordinary elements of secreting structure, there are constantly found in all the 
animals I have mentioned, excepting the Snake, a great number of rather large dark 
yellowish corpuscles imbedded in the parenchyma ; these in the Eft measured from 
Ty^ to iT^th of an inch ; their form is usually circular or rather oval, but sometimes 
irregular when several have coalesced together ; their margin is generally well-defined, 
they lie quite separate and unconnected with any other structures. I have not been 
able to determine exactly the mode of their production ; sometimes it has appeared 
that a number of dark yellow granules were grouping themselves together to form a 
circular mass ; they exhibited very active molecular motion, but were enclosed by no 
envelope ; in other instances a delicate envelope is distinctly demonstrable, and once 
I have observed a mass of similar granules enclosed in a cell with envelope and nucleus. 
It seems on the whole probable that these dark corpuscles are produced in some way 
by the agency of cells, or perhaps by their nuclei alone, and it is scarcely doubtful that 
they must be considered as products of hepatic secretion, though an eminent chemist, 
whom I requested to examine them, was unable to discover in them the usual reac- 
tions of bile. These remarkable biliary concretions (for so I think we may call them), 
occurring in the liver of reptiles, are evidently identical in their nature and import 
with the yellow masses described in the liver of fishes ; both are doubtless indications 
of imperfect excretory action ; but the deep, almost black colour of the retained pro- 
duct in the reptile, and the great deficiency of oily matters in the gland, as compared 
with that of the fish, seem to lead to the conclusion, that a vicarious relation subsists 
between the colouring and fatty principles of the hepatic secretion ; and this is borne 
out by the appearance which is presented in complete fatty degeneration of the 
human liver, compared with the same in a state of biliary congestion, the olive tint 
of the latter condition being replaced by the dull yellowish white of the former. 
In Birds the liver is of a crisper texture, and much lighter colour than in most 
reptiles ; it presents decided indications of a lobular arrangement, and in thin sections 
portal canals may be easily traced dividing into fissures. Its parenchyma varies in 
character ; in a pigeon it was remarkably free from oil-globules, and consisted almost 
entirely of nuclei and granular matter, no perfect cells being discernible ; in a swan 
{Cygnus olor) the secreting substance was of a dark greenish colour, owing to the 
presence of biliary matter, and chiefly disposed so as to form masses having a plexiform 
arrangement ; in a duck {Anas hoschus) the parenchyma was equally destitute of 
perfect cells, consisting entirely of nuclei and granular matter, with diffused oily 
particles ; there were also numerous groups, as well as separate molecules of biliary 
matter, lying free in the parenchyma, and also in the fissures by which it was traversed, 
R 2 
