310 FRANKLIN PARADISE JOHNSON 
As the portal and hepatic veins increase in length, the blood 
flow through certain capillaries along their sides is diminished 
and finally stopped, with the result that these capillaries dis- 
appear through retraction. Thus it is that capillaries arise 
from only the terminal branches of the hepatic and portal veins. 
It was Mall’s idea (06) that new lobules form by the split- 
ting up of old ones, yet he does not make clear the exact manner 
in which the splitting takes place. Apparently, he believed 
that the lobules split and become fragmented into a number 
of parts, each of which is capable of giving rise to a new lobule. 
Furthermore, he believed that the fragmented parts of several 
different lobules are capable of uniting into a single lobule, for 
on page 278 he describes a lobule as arising from three adjoin- 
ing ones. Yet his diagrams illustrating the formation of new 
lobules (figs. 41 to 43) are not suggestive of any such ‘shattering’ 
and reuniting of parts of lobules, but rather of an accumula- 
tion of orderly binary fissions; if we should add other figures 
to his diagrams to fill in the wide gaps which he has left, we 
should have similar pictures to those which I have shown in 
figures 11 to 15. 
As stated above, the manner in which the hepatic lobules of 
the pig develop may be understood from the study of any single 
stage of development. However, it is only in the later stages 
where lobule boundaries are made definite through the ingrowth 
of connective tissue that the process can be determined with 
any degree of accuracy. I have accordingly used for the 
following description a liver from a pig two months old. The 
observations recorded have been checked with other stages, 
both before and after the connective tissue septa have made 
their appearance; so far as I can determine, the formation of 
lobules is the same in all. 
The development of new hepatic lobules can be best under- 
stood by watching the changes which take place in the grow- 
ing hepatic veins. Each of their new branches marks the begin- 
ning of a new hepatic lobule. The portal veins spread over the 
surfaces of or between the lobules, dividing repeatedly, their 
terminal branches being more numerous than those of the 
