338 RICHARD E. SCAMMON 



pouches sprang and the oldest one in which the liver had reached 

 a length of 1.1 mm. as measured from transverse sections and was 

 a solid parenchymous organ. He traced the separation of the 

 liver from the gut and the formation of the gall bladder in some 

 detail and followed out in a general way the development of the 

 two larger hepatic ducts. On the whole his description is a 

 confirmation of that of Brachet. The reconstruction method 

 was apparently not employed. 



The work of Debeyre ('09) is primarily a study of the origin of 

 the hepatic cylinders. However, working on Laguesse's Acan- 

 thias material, he confirms that author's account of the early 

 stages of the liver, including the location of the gall-bladder anlage 

 in the extreme posterior end of the hepatic diverticulum. 



The papers of Braus ('96), Holm ('97), and Minot ('00) deal 

 mainly with the histogenesis and vascularization of the liver, but 

 contain incidental references to its early development. Braus 

 and Minot accept Balfour's account as essentially correct. 



III. DEVELOPMENT OF THE LIVER IN EMBRYOS FROM 3 TO 



10 MM. IN LENGTH 



In Acanthias the first evidences of liver development are to be 

 seen in embryos of 19 to 21 segments. At this stage, which is a 

 little younger than No. 16 of the Normal plate series and lies 

 between Balfour's stages G and H, the embryo shows a distinct 

 head bend and the medullary canal is closed except for the large 

 netiropore. The archenteron which is still" in quite a primitive 

 condition is outlined in figure 1, a graphic reconstruction from 

 transverse sections. The fore gut is separated from the entoderm 

 of the blastodisc and is approximately one-sixth the length of the 

 body. The lateral walls of the mid and hind gut are still sepa- 

 rated at their bases almost throughout by a considerable ventral 

 cleft, and meet only a few sections anterior to the tail to form the 

 lower and hinder walls of the neurenteric canal. The first gill 

 pouch is a shallow depression, present on one side only. The 

 second gill pouch is indicated by a very slight depression in the 

 dorsal part of the lateral wall of the pharynx immediately pos- 



