260 RICHARD E. SCAMMON 



In the area of approximately 1 mm. represented here there are 

 five bhnd buds projecting from the cyhnders into the sinusoids. 

 This method of addition to the network continues for a con- 

 siderable period. I have found no traces of new buds in the body 

 of the liver after the great increase in size of the cylinders when 

 the embryo reaches a length of about 40 mm. However, in the 

 portions of the liver which are the last to be formed, i.e., the dor- 

 sal margins and the posterior tips of the lateral lobes, this method 

 of cylinder formation continues until the embryo reaches a length 

 of 50 to 60 mm. 



While in the earlier stages of the development of the hepatic 

 network the increase comes perhaps equally from peripheral 

 and interstitial growth, in later stages the latter method is by 

 far the more important. The hepatic network terminates periph- 

 erally in a large number of blind knobs which by their growth 

 and division give rise to a large amount of hepatic tissue. The 

 cells of these terminal knobs remain in a comparatively undiffenti- 

 ated condition while those of the more central part of the network 

 are undergoing rapid changes in structure. Figure 43 shows a 

 small portion of the tip of the lateral lobe of an embryo 20 mm. 

 long. The mesothelium covering the liver has been removed. 

 Here the terminal knobs are seen projecting from the general 

 network and are often attached to the mesothelial sheath by 

 strands of mesenchyma. This specimen was prepared by cutting 

 a thick celloidin section of the region desired by the method 

 already described. The celloidin was then dissolved away and 

 the mesothelial covering stripped from the fragment with fine 

 forceps. 



The peripheral addition to the hepatic network takes place 

 at first over the entire surface of the liver. But like the inter- 

 stitial method of addition it is later limited to the tips of the 

 lateral lobes and to the dorsal margins of both the body and 

 lateral lobes of the liver which at a comparatively late stage 

 grow rapidly upward between the stomach and the lateral body 

 walls. In embryos 60 mm. in length these areas are much re- 

 stricted and they cannot be seen in an embryo 80 mm. long. 



