Royal Society. 225 



of development, are seen to be included in vesicles or short tubes 

 of homogeneous membrane, often coalescing and exhibiting a more 

 or less manifestly plexiform arrangement ; this portion of the 

 liver is regarded by Mr. Newport as really adipose tissue. The 

 author has termed it the Parenchymatous portion of the liver, on 

 account of its general appearance and mode of development, though 

 he has not been able to determine whether the tubes always origi- 

 nate from it. Among the Arachnida, the follicular type of arrange- 

 ment prevails; and the same is the case with the Crustacea, the folli- 

 cles in these last being distinctly visible to the naked eye. In Mol- 

 lusca also, we find the follicular arrangement universally to obtain ; 

 yet in certain cases the limiting membrane of the follicles cannot be 

 shown to exist, and the author therefore thinks that its importance 

 is probably not great, but that it serves chiefly to fulfil the me- 

 chanical function which its synonym " basement" indicates. The 

 quantity of retained secretion in the liver of molluscs seems clearly 

 to imply that the bile in them is not an excrementitious fluid ; it is 

 used slowly on account of the imperfect character of the respira- 

 tion. 



In passing from the Invertebrata to the Vertebrate division of the 

 animal kingdom, and beginning with the class of Fishes, a great 

 change is inimediately manifest in the form and character of the 

 biliary organ ; it is now a gland of solid texture, to which the term 

 parenchymal is justly applied. Two portions may be distinguished 

 in it, namely, the secreting parenchyma, consisting of delicate cells, 

 or very often of nuclei, granular and elaborated matters in great 

 part, and the excreting ducts, which, though completely obscured 

 bj'- the surrounding bulky parenchyma, may yet be satisfactorily de- 

 monstrated, and traced often to their terminal extremities in the 

 following manner. If a branch of the hepatic duct be taken up in 

 the forceps, it may be dissected out without much difficulty from 

 the surrounding substance, which is very soft and yields readily to 

 gentle manipulation ; when a trunk is in this way removed and 

 placed under the microscope, a multitude of minute ramifications 

 are seen adhering to it ; among these not a few may be discovered, 

 which do not appear to have suffered injury ; some are occasionally 

 seen terminating by distinctly closed extremities ; more usually the 

 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, 



Phil. Mag. S. 3. Vol. 31. No. 207. Sept. 1847. Q 



