Hatai, Origin of Netiroglia. 295 



wall, but lay close to it (Fig. 7). Between these two appear- 

 ances, various intermediate stages could be easily found. In 

 some cases a tip of the nucleus is still attached to the capillary 

 wall, while the rest of it has become separated (Figs. 5, 6). 

 This appearance suggests very strongly the migration of the 

 nucleus from the capillary wall into the surrounding tissue. It 

 is known that leucocytes escape from the capillary wall and 

 exhibit amoeboid movements, but their nuclei are easily distin- 

 guished from those of the endothelial cells by their structure as 

 well as their size ; the former being very much smaller than 

 the latter. 



As soon as the nuclei are separated from the capillary 

 wall, they become amoeboid and migrate away from the capil- 

 lary. The following observation is in favor of the above con- 

 clusion. A large number of the mitotic figures of various 

 phases in the nuclei of the capillary wall are often visible. In 

 such a locality where the mitoses are abundant, the nuclei are 

 so closely placed that in some cases, the one nucleus overlaps 

 the other the outermost nucleus projecting outwardly, thus 

 showing the first step of the migration. 



From these observations the conclusion is drawn that the 

 neuroglia nuclei in the white rat as well as in the mouse repre- 

 sent two distinctly characterized types ; namely, nuclei the 

 structure, of which resembles very closely that of the nerve 

 cells (type a), and the nuclei, the structure of which resembles 

 very closely that of the endothelial cells which form the capil- 

 lary wall (type b). These two types of nuclei have been de- 

 rived from the ectoblast and the mesoblast respectively. The 

 latter (type b), has probably two sources of origin ; that is, 

 they are partly derived from mesoblastic cells immigrating from 

 the meninges (Capobianco and Fragnito), and partly from 

 proliferating endothelial cells of the walls of the capillaries, 

 these cells having separated from the capillary wall and migrated 

 into the surrounding tissue, where they constitute one type of 

 the neuroglia elements. 



