57 



The nuclei contain one or several true nucleoli and a chromatin net- 

 work with numerous net-knots (Fig. 11 c). They possess an extensive 

 shell of granular, pale staining cytoplasm. This is the megaloblast 

 (Fig. 12 c). These cells are still slighly amoeboid (Fig, 10 d^). The 

 final normoblast is small in size, spheric in shape and with a deep 

 staining central nucleus (Figs. 11 and 12 d^). The latter contains one 

 or several nucleoli. The cytoplasm is homogeneous and stains deeply, 

 a condition due probably to the presence of hemoglobin. Figure 11 

 illustrates a large blood island with its forming endothelial wall and 



Fig. 11. Drawing of blood island of older vesicle, illustrating the stages in 

 hematopoiesis : a^ and a^ mesenchyme cells; a" endothelioblasts becoming 'lymphocytes" 

 (Maximow) ; b^ and b'- "lymphocytes" ; c megaloblasts ; d^ and d- normoblasts ; R bi- 

 nucleate giant cell. X 1500. Reduced ^/^ in reproduction. 



the several types of blood cells: h^+^ lymphocytes; c megaloblast; 

 d^+^ normoblasts; e erythroblast (Fig. 12). Many of the cells assume 

 polyhedral shapes due to pressure. The various spaces between the 

 cells represent the lumen of the forming vessel. In Fig. 11 also are 

 shown (a^) several endothelial cells, that are characterized by the small 

 pale-staining nuclei and their paler homogeneous cytoplasm and 

 generally oval shape. They are present only in small numbers both 



