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RICHARD E. SCAMMON 



posterior part of the median lobe of the Uver. The cross sections 

 of cylinders were taken at random from this region, except 

 that those lying in the rapidly growing peripheral zone were 

 avoided in each case. 



In the first specimen of the series the number of cells bounding 

 the lumen in cross section averages 12.5. The diameter of the 

 tubules has become more uniform and averages 58 micra. Ex- 

 amples of such tubules are illustrated in figure 31. At about this 

 time the liver begins to increase greatly in size. This growth is 

 due in part to the actual increase in number of hepatic cells, as 



TABLE 1 



Measurements of the hepatic cylinders in Acanihias embryos 



is indicated by the presence of numerous mitotic figures in the 

 hepatic cylinders, but a much greater part of the increment is 

 due to the establishment of the huge hepatic sinusoids. With 

 this increase in size of the sinusoids the tubules are distinctly 

 reduced in size, their average diameter dropping from 58 micra 

 in an embryo 15 mm. in length to 37.6 micra in one 25 mm. and 

 35.6, in one 28 mm. in length. This reduction in diameter may 

 be due somewhat to the decrease in the size of the lumen, but is 

 caused mainly by the actual decrease in the number of cells 

 surrounding the lumen at any one plane. The process is a con- 

 tinuous one after anastomosis is established, but is more rapid 



