HISTOGENESIS OF THE LIVER 247 
tomes, the liver is indeed a true compound branching gland, 
as has been shown by the work of Retzius ('92), Holm ('97), 
Cole ('13) and others. In Petromyzon, however, anastomoses 
occur occasionally in the embryo (Brachet '97) and are very 
numerous in the adult (Renaut '97). On the side of embryology 
little evidence of this modification has been offered, although 
the statement that the liver arises in many vertebrate embryos 
as a branching gland, and that it takes on its adult reticular 
structure through the anastomoses of its end pieces, is common 
enough in texts. But an examination of the literature shows no 
more complete account of this early period of the histogenesis 
of the liver than that given by Remak ('55) excepting Hilton's 
work ('03) on the pig which has hardly received the attention 
that it deserves. The study of the actual course of the anasto- 
mosis of the end pieces has also been neglected, and the only 
clear statement to be found regarding this process is not in 
connection with the liver at all but in Laguesse's ('96) description 
of the histogenesis of the pancreas where he found numerous 
anastomoses at different stages. 
The literature of the histogenesis of the liver in selachians 
is scanty and has been to a large extent reviewed in the com- 
prehensive works of Oppel ('00) and Fiessinger ('11). 
Balfour's ('76) account was the first to appear and as it has 
formed the basis of all later descriptions, it is given here in full: 
By stage K the hepatic diverticula have begun to bud out a number 
of small hollow knobs. These rapidly increase in length and number 
and form the so-called hepatic cylinders. They anastomose and unite 
together so that by stage L there is constructed a regular network. 
As the cylinders increase in length their lumen becomes very small 
but appears never to vanish. 
Hammar ('93) in the course of a study devoted particularly 
to the development of the larger hepatic structures illustrates the 
development of the hepatic cylinders in two models of the liver 
of Torpedo embryos corresponding in development to Balfour's 
stages L and M. He makes no comment upon them aside from 
stating that the trabeculae increase in number and decrease in 
caliber in the period intervening between the two stages. 
