THE DEVELOPMENT OF THE VASCULAR SYSTEM 



273 



of homogeneous or finely granular, slightly basophilic cytoplasm containing 

 either a single tabulated, annular nucleus (megakaryocytes , Fig. 250, meg) 

 or many nuclei (polykaryocytes). The polykaryocytes have been considered 

 identical with the osteoclasts, which may represent fused osteoblasts, but 

 this relationship has not been definitely established. Both kinds of cells 

 have been considered as derivatives of the myeloblasts, the polykaryocytes 

 being later stages of megakaryocytes. 



The blood platelets are now regarded by some authors as derivatives of 

 the megakaryocytes; pseudopodia of the latter breaking off and gaining 

 access to the blood stream. By others they are not believed to be formed 

 constituents of the circulating blood, but appear only after shed blood 

 comes in contact with a foreign substance. 



The accompanying table, which is a tentative graphic scheme of the 

 monophyletic theory, will assist the student in tracing the lineage of the 

 blood cells. 



Primitive lymphocyte (Maximow) 

 Primitive blood cell Haemoblast 



Primitive 

 blood cell 



/ 



Lymphocytes 



Polymorph 



Granular Non-granular 

 \ l\ 



Momonuclear \ Mononnclear 



Transitional I Transitional 



Neutrophile Basophile Basophile 

 Acidophile Neutrophile Acidophile 

 Acidophile Neutrophile 



\ 

 Megaloblast 



Normoblast 

 Erythroblast 



Erythrocyie 

 \ 

 Megaloblast 



etc. 



Primitive 

 blood cell 



Lymphocytes 



THE LYMPH VASCULAR SYSTEM. 



A controversy has arisen over the origin of the lymph channels and their 

 endothelium, similar to the one that arose over the genesis of the blood vessels. 

 There are therefore two main views, viz.: (i) that the endothelium of the 

 lymph vessels arises as sprouts from the endothelium of veins and continues 

 to grow by proliferation and migration of its own cells, the lymphatics thus 



