246 RICHARD E. SCAMMON 



distinguish the selachian liver are not manifested until a com- 

 paratively late stage in the development of the organ. In 

 earlier stages characters common to the liver in all vertebrates, 

 but which are often masked or modified in higher forms, are 

 shown with unusual clearness. It is chiefly with these more 

 fundamental characters such as the formation and anastomoses 

 of the hepatic cylinders, the differentiation of the minor bile 

 ducts and the relation of the parenchymatous and vascular 

 structures in the liver, that this paper has to do. The specific 

 characters of the selachian liver, which have been mentioned, 

 have been considered only incidentally. 



The main material employed in this study consisted of embryos 

 of Squalus acanthias, but specimens of Raia batis. Torpedo 

 ocellata, Mustelus canis, Mustelus laevis and Squatina angelus 

 have been used for supplemental and comparative work. For 

 a large part of the Acanthias material, and for the specimens 

 of Mustelus laevis, I am particularly indebted to the late Dr. 

 Charles S. Minot, who not only permitted the removal of 

 numerous series from the Harvard Embryological Collection, 

 but also provided special material for use in this work. 



DEVELOPMENT OF THE HEPATIC CYLINDERS 



1. Literature 



Our conception of the glandular structure of the vertebrate 

 liver rests upon a large number of observations made mainly 

 in the first half of the last century and culminating in the work of 

 Eberth ('66) and Herring ('72). Since that time it has been 

 recognized that the liver is -a compound gland with a more or 

 less regularly branching system of ducts and with a terminal 

 network of anastomosing end pieces, and our knowledge of the 

 details of this network has been greatly extended by the Golgi 

 method in the hands of Retzius ('92), Hendrickson ('96) and 

 others. 



It is generally stated that the anastomotic type of liver is a 

 modification of the compound branching gland type; Of this 

 the best proof is the phylogenetic one, for in the lower cyclos- 



