DEVELOPMENT OF LIVER AND PANCREAS 



223 



capillary circulation in this network has progressed. In the 

 11 and 12 mm. embryos there is a confusing network of trabeculae 

 and it is difficult to differentiate the main ducts from the hepatic 

 columns. Shore believed that in the frog the tubules were first 

 solid and that later a lumen developed. Goette expressed the 

 opinion that a lumen was present from the earliest formation, 

 though he admitted this was hard to demonstrate. The reason 

 of the difficulty of proving this either way is apparent. How- 

 ever, from a study of sections of Amblystoma it would seem 

 that a lumen is present from the earliest stages. 



Fig. 5 Transverse section of embryo 9 mm. long. X 30. F.g., foregut; L, 

 left portion liver; R, right portion liver. 



Fig. 6 Transverse section of an embryo 11.5 mm. long. X 30. F.g., foregut; 

 GB., gall-bladder; L., liver. 



3. Position of the organ during development 



At a stage represented by 11.5 mm. embryos there is a shift- 

 ing to the right particularly of the caudal end of the liver (fig. 6). 

 Such a shifting of the posterior part of the liver was noted at a 

 later stage in Necturus by Eycleshymer and Wilson ('10) and 

 others. The reason for this lateral ward shifting is probably the 

 pressure of the rapidly growing stomach and duodenum which are 

 beginning to take a ventral and sinistral position. It is possible 

 also that the spleen which is now a prominent organ in the left 

 dorsal region of the body cavity has some influence on this 



