480 
DR. C. HANDFIELD JONES ON THE 
of cells constituting a linear series. Finally, I have several times noticed that the 
formation of young cells takes place chiefly at the extremities of the rows ; I do not 
mean at the margin of the lobule, but in those which were seen projecting from a 
broken edge ; in one instance a young cell had formed at the extremity of a row of 
four, it was distinguished by its smaller size, more distinct nucleus, and the absence 
of granular or oily contents ; in front of it was a large and very distinct nucleus, 
with only a trace of cell-wall on one side. This would seem to indicate that the 
organic force which determines the formation as well as the growth of the cells is 
exerted chiefly in the longitudinal direction, i. e. in the axis of the row. The obser- 
vations now related have an interesting correspondence with those recorded with 
respect to the behaviour of the cells at the margin of the lobule ; in both instances 
the mature cell appears to dehisce in order to give exit to its elaborated contents ; 
but in the one case this takes place into the cavity of the next cell ; in the other, into 
the cavity of the surrounding duct. From all these observations, strengthened by 
the analogy to be mentioned, the following theory may perhaps be considered pro- 
bable : — The mode of development of the Haversian canals in bone, of the primitive 
nerve tube and muscular fibre, presents us with examples of cells arranging them- 
selves in linear series, very similar to those which we have described in the lobules of 
the liver ; these cells thus arranged coalesce, and form the elementary parts of their 
respective tissues. In the liver the same type of arrangement seems to prevail ; each 
linear series may be conceived to represent a primary duct tubule, the cavity of 
which remains divided by septa formed by the walls of contiguous cells ; these septa 
at intervals give way, and by some unknown force (perhaps a vis a ter go, from 
accumulated secretion) the elaborated material is passed on to the next in order ; a 
similar process being repeated in each cell of the series, till, by the dehiscence of the 
terminal one, the secretion is set free in the cavity of the duct. 
Appendix. 
The condition of the cells with regard to their coalescence is very various ; in 
livers of sheep examined during the winter, a section, however thin, has been so 
opake that no satisfactory view could be obtained of it ; in such the cells are found 
gorged with particles of secretion, and seldom, if at all, communicating ; the base- 
ment membrane of the ducts has also a semi-fibrous aspect, and it is rare to observe 
the margin in an active condition. These facts, and the circumstance that the fusion 
of the cells is not so frequent in any case, as we should expect if it were essential, 
have led me subsequently to believe that a process of transmission may go on through 
the septa of the rows of cells and basement membrane, though there can be no doubt 
that it must proceed much more rapidly when the cells have coalesced and the base- 
ment membrane disappeared. 
