24 



of three contiguous tubules. The cells lining A are very similar to 

 the cells lining the vesicle. They are slightly more flattend and ir- 

 regular, a result to be expected under pressure. In B is shown a later 

 stage. Here the cells have become cubic, the cell-borders are growing 

 indistinct and the nuclei are small and pale. A late stage shown in 

 C illustrates the extreme type of flattened epithelium in the tubules. 

 Cell borders are entirely lost, the cytoplasm stains more deeply, and 

 the nuclei are quite small and pale. 



( '\ 



Fig. 9. 



Fig. 8. Drawing of cross section of cord of cntodermal cells from the older 

 vesicle showing the general character of the cells, and the connective tissue sheath of 

 the cord. The cytoplasm appeal's to be disintegrating, the deeply staining flakes prob- 

 ablj' representing cell detritus; whereas some of the nuclei appear healthy. Original 

 magnification 1000 diam. Reduced V, in reproduction. 



Fig. 9. Drawing of four typical entodermal cells from the wall of the older vesicle 

 in the region where the lining epithelium is stratified. Original magnification 1750 diam. 

 Reduced ^l„ in reproduction. 



The larger cells of the tubules are in all respects similar to 

 those lining the main cavity. Their cytoplasm is much vacuolated. 

 The nuclei are large, centrally placed, and contain usually several 

 nucleoli. Whether the vacuoles represent fat or are the result of 

 secretory activity or degeneration cannot be determined here. There 

 are also here numerous flakes of more deeply staining substance (Figs. 7 

 and 8). The general structure both of the tubules and the cells lining 



