386 RICHARD E. SCAMMON 



V. GENERAL SinVIMARY 



The observations here recorded may be summarized as follows: 



1. The hver arises in Acanthias embryos of from 20 to 25 seg- 

 ments as a pair of shallow lateral diverticula from the lateral walls 

 of the ventral half of the gut. These diverticula extend both 

 behind and in front of the anterior wall of the yolk-stalk, 



2. The growth of the fore gut posteriorly through the coales- 

 cence of the lateral walls of the yolk-stalk causes the lateral hepatic 

 diverticula to lie mainly in front of the anterior wall of the yolk- 

 stalk in later stages. 



3. The median ventral liver pouch described by Balfour and 

 others is, in Acanthias at least, a secondary structure produced 

 by the fusion of the anterior ends of the primary lateral diverticula. 



4. Three distinct secondary parts are derived from each primi- 

 tive lateral hepatic diverticulum. The anterior portion goes to 

 the median hepatic pouch. The upper part of the middle por- 

 tion forms the lateral hepatic pouch. The posterior part goes 

 to form a posterior connecting segment between the liver and gut. 

 This has been termed the pars ductus lateralis and later becomes 

 a part of the ductus choledochus. 



5. At an early stage the liver shares in the left to right rotation 

 which produces the spiral valve in the intestine and the lateral 

 vitelline groove in the yolk stalk. 



6. The median hepatic pouch is somewhat differentiated into 

 two parts : an anterior one, the pars hepatica mediana to which the 

 lateral pouches are mainly attached and which gives rise to hepatic 

 trabeculae, and a posterior one, the pars ductus mediana, which 

 forms the anterior part of the ductus choledochus. 



7. The anterior part of the left hepatic duct is formed from the 

 left hepatic pouch and the left part of the pars hepatica mediana. 

 The anterior part of the right hepatic duct is formed from the 

 rfght hepatic pouch alone. 



8. The hepatic ducts and ductus choledochus are very markedly 

 rotated to the right about a vertical axis in a comparatively late 

 stage. This rotation is probably due to the great growth of the 

 left omphalo-mesenteric vein and the formation of a venous 



