16 H. E. JORDAN 



thrown into the surrounding mesenchyme, as in the allantoic 

 spleen grafts of DanchakofT, will not differentiate into a leucocyte, 

 but into an erythrocyte. A mature endothelial cell does not 

 normally, as originally, differentiate into a hemoblast. And an 

 extra vascular hemoblast which is in process of differentiation into 

 a granulocyte apparently cannot redifferentiate into an erythro- 

 cyte after it has wandered into the blood-vessel lumen. 



SUMMARY 



The results of this study of the umbilical cord of the pig, 

 which maintains to full-term largely the embryonic condition 

 of the original body-stalk, emphasize the polyvalent capacity 

 of the mesenchymal cell and its hemoblast derivative, and supply 

 further evidence in agreement with the monophyletic view of 

 hemogenesis. The multinucleated hemogenic giant-cell fur- 

 nishes the same essential stimuli for the differentiation of erythro- 

 cytes as does an inclosing endothelium. It is comparable to a 

 blood-island, and produces erythrocytes intracellularly in a 

 manner similar to that by which erythrocytes separate out of 

 a blood-island syncytium. This tissue demonstrates also the 

 origin of endothelium both by adaptation of mesenchyme about 

 a blood-island and by vacuolization and fusion of vasofactive 

 mesenchymal cells. It shows, moreover, that the lumen of the 

 original blood-vessels includes both inter- and intracellular 

 contributions. 



