312 CHARLES R. STOCKARD 



cells' since they may form either white or red corpuscles. Yet 

 in the yolk islands of the Fundulus embryos without circulation 

 only red blood cells, erythrocytes, are produced and they remain 

 in this location to be observed throughout embryonic Ufe. The 

 evidence for Maximow's position seems to me somewhat insuffi- 

 cient. 



During the summer of 1914, I had the privilege of examining 

 Mme. Dantschakoff 's preparations which both she and Maximow 

 cite in support of the monophyletic theory of blood cell origin. 

 One so inchned might interpret these specimens as showing that 

 the red and white corpuscles do arise from the common stem 

 mother cell. The youngest lymphocytes were invariably scat- 

 tered among the mesenchymal cells while the erythroblasts were 

 budded off into more or less well defined vessels. No one could 

 emphatically state that the two classes of blood corpuscles had 

 ever actually divided off from any one single mother cell. 



The more or less constant separation of the early leucoblasts 

 and erythroblasts, as is also shown in Maximow's figures and those 

 of other workers, would seem to indicate their origins from two 

 different mother cells. If one mother cell only forms or divides 

 off cells which develop into lymphocytes or leucocytes and 

 another mother cell gives rise to only erythroblasts, then there 

 is no reason to say that the two mother cells were the same 

 although they appeared to be two similar mesenchymal cells. 

 They were potentially different, and this potential difference is 

 all that the diphyletic notion of blood cell origin demands. A 

 careful study of the embryos without a blood circulation will 

 demonstrate the fact of this different origin of white and red 

 corpuscles. 



Maximow then advocates the last clause in the monophyletic 

 code, and states that the intravascular primitive blood cells are 

 not only increased by mitosis but are also added to by the pro- 

 duction of the same kind of cells from the fixed endothelial wall 

 of the primitive vessels. Endothelial cells may wander away 

 into the mesenchyme or may wander into the vessel lumen. 

 One often sees according to Maximow a cell project into the 

 vessel, its body assumes a rounded form and its protoplasm 



