118 
DR. C. H. JONES ON THE STRUCTURE 
the usual kind, nuclei, cells, and abundant granular and oily matter, with some yel- 
low masses which seemed to consist of concrete biliary substance. 
In concluding this imperfect survey of the structure of the liver in the Invertebrate 
sub-kingdom, we may recapitulate by observing, that the tubular or follicular type 
of arrangement is that which generally prevails, and to which a tendency is almost 
invariably manifested ; yet it has been shown to be probable in several instances, that 
a more or less considerable portion of the gland is in a condition which may be 
termed parenchymatous, the secreting structure being interstitially situated and not 
in connection with any excretory duct. In the next great division of animals at 
which we arrive, the hepatic apparatus is constantly distinguishable into a tubular 
and parenchymatous portion, but the latter now preponderates immensely, and the 
office of the tubular structure is confined to serving as an excretory duct; the evi- 
dence of this will clearly appear in the class of Fishes, which will next be investigated. 
With the exception of the curious Lancelot {AmpMoxus), the liver in all fishes may 
be stated, on the authority of Professor Owen, to be a parenchymatoid organ, provided 
with efferent hepatic ducts, and usually a gall-bladder and cystic duct, which pour 
the secretion into the duodenum. The blood-vessels entering the liver are now of 
different kinds, the portal vein or veins supplying altogether the parenchyma, while 
the hepatic artery is devoted principally to the ducts: this circumstance I think has 
not yet been fully accounted for ; it will again attract our attention when we consider 
the manner in which the secretion is conveyed into the excretory ducts. Respecting 
the actual structure of the liver in Fishes, as in all Vertebrate animals, our knowledge 
has hitherto been very imperfect ; for though, if I may use the term, the geography 
of the organ was perfectly set forth by Mr. Kiernan, yet since we have become ac- 
quainted with the actual agents in the process of secretion, the cells which elaborate 
the bile, and which constitute so very large a part of the organ, it has remained a 
complete mystery how the ultimate bile ducts were disposed with relation to the cells, 
and in what manner the secretion when formed was conveyed into the excretory pas- 
sages. Before giving an account of the observations I have lately made respecting 
these points, I ought perhaps to mention that, according to Dr. Williams, the struc- 
tural arrangement in fishes is nearly the same as in the molluscous tribes, the secreting 
cells being enclosed (he deems) in tubes of homogeneous membrane; this, however, 
is so completely contradicted by all that I have seen, that I shall do no more than 
thus cursorily allude to it. As it appears to me that in Fishes, the lowest of the Ver- 
tebrate classes, we find the liver at once assuming a very different type of arrange- 
ment from any which it has hitherto exhibited during our survey of the animal series, 
it is evidently a matter of great importance to determine, if possible, its real consti- 
tution, and to understand in what the essential change consists which has produced 
so marked a difference of form and character ; fortunately this is rendered more prac- 
ticable by the circumstance, that in the liver of fishes there is comparatively a small 
quantity of fibrous tissue (corresponding to the capsule of Glisson) diffused throughout 
