264 RICHARD E. SCAMMON 



development and in which the cyHnders are reduced to slender 

 tubes. Figure 42 is from a somewhat older specimen in which 

 the cylinders have again begun to increase in diameter. The 

 changes in the number of cells surrounding the lumen of the 

 cylinder in cross section are shown in the four figures forming 

 plate 3. 



My remarks' upon the changes in the finer structure of the 

 hepatic cells can be regarded as little more than notes made in 

 the course of the general study of the growth of the cylinders. 



During the development of the hepatic tubules and cylinders, 

 the nuclei of the cells forming them are modified in shape, size 

 and structure. At the time when the tubule ridges first appear 

 upon the hepatic pouches the hepatic nuclei are elongately oval 

 in outline, their longer axes averaging from 14 to 15 micra and 

 their lesser axes from one-third to one-half of this length (fig. 28).^ 

 With the definite outpouching of the hepatic tubules the nuclei 

 become broader and shorter, but their volume remains practi- 

 cally unchanged (figs. 29, 30). In an embryo 10 mm. in length 

 (S.C. 20) from which tubules have been described and figured 

 in the preceding part of this paper, the hepatic nuclei average 

 8 micra in diameter and 11 micra in length. Anastomosis has 

 apparently no effect upon either the size or structure of the nuclei. 

 In embryos from 10 to 20 mm. long one can follow the change 

 in shape of the majority of the nuclei from broadly oval to spheri- 

 cal bodies. In a 20.6 mm. embryo (H.E.C. 1494, fig. 32) the 

 great majority of the nuclei are spherical and have a diameter 

 of 10 micra. Thereafter they gradually decrease in size even as 

 the cells grow in size through an increase in fat content. In an 

 embryo 47.3 mm. long (S.C. 11) the average diameter of the 

 nuclei is 7.5 micra and in one of 95 mm. (H.E.C. 1882) it is little 

 if any less. As the fat accumulates in the liver cells the nuclei 

 may again change in shape, being in many cases pressed against 

 the margin of the cell and assuming an oval or crescentic outline 

 suggesting the form of the nuclei found in true fat cells. The 

 nuclei which remain spherical have an average diameter of 7 

 micra or a little less (in embryos 200-240 mm. long). 



^ All measurements given here were made from paraffin sections. 



