AND DEVELOPMENT OF THE LIVER. 
119 
the gland, which therefore separates much more readily into its elementary parts: I 
have endeavoured to take advantage of this peculiarity to ascertain the actual con- 
dition of the ultimate hepatic ducts, and I trust that I have in some measure suc- 
ceeded, Taking up a main branch of the duct, I find that by gentle traction and 
lacerating the surrounding parenchyma, I can isolate it with a multitude of ramifica- 
tions without much ditficulty, and after gentle washing remove it to a slip of glass. 
When now the specimen is spread out, and covered with a thin lamina, it can be 
conveniently examined : some of the branches, especially the larger ones, are evidently 
broken across, but a great number of the smaller ramifications do not appear to have 
suffered injury, and their characters may be thus described. They have a diameter 
of 10 00-5 oo fb of on inch at their origin from the trunks ; they run a remarkably 
long course, giving off very few branches, and those for the most part at long inter- 
vals, though sometimes a group of minute branches arise close together ; they taper 
slowly towards their extremities, which are found in various conditions, sometimes 
undoubtedly closed, with a defined rounded margin formed by homogeneous mem- 
brane ; this however is rare ; more usually the structure towards the extremity 
becomes less distinct, and it seems as if the duct gradually ceased. The larger ducts 
and the smaller at their commencement are invested by a thin layer of fibrous tissue ; 
within this is a distinct basement membrane, which extends beyond the fibrous layer 
for a variable distance ; sometimes it forms the rounded closed extremity of the duct, 
but mostly it becomes gradually faint, and can only be supposed to exist by the duct 
still exhibiting a well-defined margin ; in many instances it certainly ceases some 
way from the terminal extremity. The contents of the ducts vary considerably ; in 
the larger ones there may be either nuclei with granular matter forming an epithelial 
layer, or very delicate and pellucid vesicles; or the cavity may appear transparent, 
containing only some finely-mottled substance. Advancing to the smaller ducts, we 
find that they may likewise contain pellucid vesicles, so large as to occupy their whole 
cavity, but more frequently they are filled with nuclear granules and granular matter, 
the nuclei again being often very indistinct, so that there is scarce anything but gra- 
nular matter to be detected ; when they are in this condition the basement membrane 
also has generally disappeared, and the aspect of the duct, some way before its ter- 
mination, is that of a tract of granular matter, which preserves accurately the tapering 
form and course of the original structure. In some cases the fibrous coat is pro- 
longed further than usual, being continued as a filamentous expansion into the sur- 
rounding parenchyma beyond the terminal extremity of the duct. The foregoing 
description expresses the results at which I have arrived from numerous dissections 
of the liver in marine fishes ; in the Perch {Perea), however, I have observed a con- 
dition of the ultimate ducts which differs from that now described in some respects, 
but resembles exactly that which is found in the mammalian liver; instead of ap- 
pearing as minute cylinders of granular matter in which nuclei are scarcely per- 
ceptible, these ducts consist almost wholly of small nuclei set close together in a 
