AND DEVELOPMENT OF THE LIVER. 
117 
acquainting- me with several instances where it is certainly absent from glandular 
structure; thus, in the pancreas of a pigeon, I recently ascertained the total absence 
of limitary membrane from the ultimate vesicles, the epithelium being arranged into 
follicle-shaped masses and tubes, the form of which was solely preserved by the 
cohesion of the particles together. In the Common Oyster {Ostrea) I notieed a 
similar instance ; here, besides the well-known follicular liver, there is a thin lamella 
of reddish brown aspect, which lies between the mass of the liver and ovary and the 
adductor muscle in contact with the intestine, to which it adheres pretty firmly. In 
structure this consists of numerous cells aggregated together, and set as it were in 
an imperfectly fibrous tissue ; these cells measure about i smoo th of an inch diameter, 
and are provided with an envelope enclosing biliary -looking granules, which some- 
times fill them completely: nuclei are rarely to be seen in them, but free nuclei and 
young cells occur in the uniting tissue. Now these cells, which seem to belong to 
the hepatic apparatus, from the nature of their contents, are certainly not contained 
in follicles or any envelopes of limitary membrane, but lying interstitially fulfill with- 
out doubt a work of secretion. This view of the non-essentiality of the basement tissue 
was promulgated some years ago by the distinguished physiologist who gave the 
membrane its name and pointed out its wide-spread extent. To illustrate a condition 
of the liver not uncommon among Mollusca, I may mention the examination of a Fresh- 
water Snail {Limnceus stagnalis), which I made during the cold spring of last year ; 
the organ was of very dark aspect and soft consistence, and its basement tissue was 
scarcely discernible; the secreting structure consisted of a large quantity of amor- 
phous and biliary matter in a free state, with numerous cells, some of which exhibited 
an envelope, an interior nucleus, and granular or biliary contents ; others were 
merely pale granular bodies : these cells seem to originate as delicate vesieles having 
a mean diameter of 2-^^th of an inch ; they acquire pale granular contents, and 
probably, at some period of their existence, nuclei ; but from observation of this and 
several others of the lower animals, it has seemed difficult to believe that tlie energy 
of the cell is always dependent on the presence of a nucleus. In the higher animals 
I think this is certainly the case, and yet there would appear even in them to be an 
exception in the fat cells, which vary so much in size, that it seems certain their 
growth must continue long after the disappearance of the nucleus. A circumstance 
which was very striking in the examination of the liver of the Limneeus, was the 
prodigious quantity of dark biliary matter which was accumulated in it ; in many 
parts it seemed as if the follicle-shaped masses were perfectly solid, converted, one 
might almost say, into biliary calculi. This state of the secreting apparatus must 
surely be conceived to imply a very tardy and imperfect discharge of the elaborated 
matter, and accords well with the imperfect character of the respiratory proeess. In 
a Sepia, one of the most highly organized among the Mollusca, the liver was still 
found to be of the follicular type; the terminal cavities were however very short and 
wide, and the limitary membrane by no means conspicuous: the contents were of 
