226 THE LIVER. 



sepamtely. I have not followed in detail the further growth 

 of the gland. It is, however, easy to note that while the 

 ductules grow longer and become branched, vascular processes 

 grow in between them, and the whole forms a compact glandular 

 body in the mesentery on the dorsal side of the alimentary 

 tract, and nearly on a level with the front end of the spiral 

 valve. The funnel-shaped receptacle loses its original form, 

 and elongating, assumes the character of a duct. 



From the above account it follows that the glandular part 

 of the pancreas, and not merely its duct, is derived from the 

 original hypoblastic outgrowth from the gut. This point is 

 extremely clear in my preparations, and does not, in spite of 

 Schenk's observations to the contrary^ appear to me seriously 

 open to doubt. 



The liver. 



The liver arises during stage I as a ventral outgrowth from 

 the duodenum immediately in front of the opening of the 

 umbilical canal (duct of the yolk-sack) into the intestine. 

 Almost as soon as it is formed this outgrowth developes two 

 lateral diverticula opening into a median canal. 



The two diverticula are the rudimentary lobes of the liver, 

 and the median duct is the rudiment of the common bile-duct 

 (ductus choledochus) and gall-bladder (PL XI. fig. 9). 



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 (PL xviii. fig. 5). 



The mode of formation of the liver parenchyma by hollow 

 and not solid outgrowths agrees with the suggestion made in 

 the Elements of Emhryologjjy p. 133, and also with the results 

 of Gotte on the Amphibian liver. Schenk has thrown doubts 

 upon the hypoblastic nature of the secreting tissue of the liver, 

 but it does not appear to me, from my own investigations, that 

 this point is open to question. 



1 Lchrbuch d. verr/leichendeu Emhryolorjic. 



