300 FRANKLIN PARADISE JOHNSON 
ment of Mall (06), lobule formation is not complete at this 
time, for I find with Lewis (712) that ‘‘the multiplication of 
lobules continues long after birth.”’ The few late stages of the 
pig which I have been able to procure, consequently, have 
been of great value in furnishing evidence concerning the de- 
velopment of the hepatic lobules. 
Because of the importance of the connective tissue septa, 
I have found it advantageous to divide the development of the 
pig’s liver into two definite periods—one before and one after the 
septa are indicated. I shall speak of the former simply as the 
‘early stages,’ of the latter as the ‘late stages.’ The early stages 
include those up to but exclusive of an embryo of 254-mm. 
in length; the later stages include the 254-mm. embryo and 
extend to the adult. 
In attempting to determine the manner in which the units 
of the liver multiply, I first gathered together a series of se- 
lected stages of developing livers. But so far as lobule forma- 
tion is concerned, this was unnecessary. I agree with Mall, 
(06) when he says, ‘‘the great difficulty is to recognize the 
same thing from step to step,’”’ but I find the greatest difficulty 
is to recognize the limits of a lobule in its three dimensions in 
any single early stage. In the later stages, however, because 
of the presence of the connective tissue septa, the lobules are 
definitely bounded. Since in any developing liver the lobules 
present numerous instances of every stage of development, 
it is possible by a little study to arrange the various stages in 
their proper sequences. In this manner the development of 
the liver lobules may be easily and most satisfactorily deter- 
mined from any single late stage. 
Inasmuch as I have worked out the development of the liver 
lobules from stages in which the connective tissue septa are 
present and continually growing and delimiting new lobules, I 
found it necessary to study first the origin of the septa. This 
was the more essential, for an understanding of the different de- 
velopmental stages of the septa makes it possible not only to 
recognize dividing lobules, but to distinguish between the newly 
formed and the old lobules. 
