HISTOGENESIS OF THE LIVER 249 



Debeyre ('09) made use of observations upon the development 

 of the hepatic cyhnders in Acanthias to lay the ghost of the 

 theory of the mesodermal origin of the hepatic parenchyma, 

 which had been again raised a short time before by Geraudel 

 ('07). He gives no complete or detailed history of the cylinders 

 but notes, with illustrations, their general appearance in embryos 

 16, 22, and 30 mm. in length, respectivel3^ In the latter he 

 recognized the beginnning of a period of pronounced increase 

 in the diameter of the cylinders. Debeyre noted the presence 

 of numerous granules in the apices of the hepatic cells and bases 

 upon this the interesting suggestion that the liver may serve 

 as an organ of internal secretion during a part of embryonic 

 life. 



2. Early development of the hepatic tubules 



In this account the structures which have been variously 

 termed hepatic cords, trabeculae, cylinders and tubules will 

 be spoken of as tubules as long as they remain as portions of 

 simple or branching unanastomosed glands. The term hepatic 

 cylinders will be employed for the same structures after the 

 process of anastomosis has taken place. 



The exact time when the anlagen of the hepatic tubules first 

 make their appearance is somewhat variable. In general they 

 are first to be seen in embryos from 7.5 to 9 mm. in length, being 

 somewhat younger than Balfour's stage K^ and corresponding 

 to numbers 22 and 23 of the Normal plate series. Such embryos 

 have from fifty to sixty-five segments and four or five pairs of 

 gill pouches of which the anterior three or four may open extern- 

 ally. The spiral valve is in the process of formation, making 

 at this time one or two complete turns of the intestine and the 

 vitelline duct is reduced to a short wide canal. The form of 

 liver anlage at this stage is represented somewhat diagrammati- 

 cally in figure 1. The organ consists of a ventral median pouch 

 from the foregut just anterior to the vitelline duct. The anterior 



2 In correlating embryos with stages of Balfour's series only the general develop- 

 ment of the embryo has been considered and not the state of development of the 

 organ under discussion. 



