282 CHARLES R. STOCK ARD 



also are within the tissue spaces and not in the vessels. None 

 of these cells are found in associations with the early red blood 

 cells. 



I have examined a number of smears of heart blood, spleen 

 pulp, bone marrow and peritoneal fluid from adult Funduli and 

 have found within these specimens numerous coarse granular 

 leucocytes, lymphocytes and various types of wandering cells. 

 The embryonic cells above described all show a more or less 

 degenerate appearance, but if they can be classed as any type 

 of white blood cell their origin is definitely removed and entirely 

 distinct from that of the red blood cell. In appearance they 

 are as closely similar to embryonic leucocytes as are the cells 

 designated by other investigators to be of that nature. It 

 seems to me that the only possible method of differentiating 

 between the origins of white corpuscles and red blood cells is 

 to prevent their association in the circulating body fluids. These 

 experiments along with numerous observations do show that the 

 red blood cells arise in a region distinctly separated from those 

 localities in which the white blood corpuscles are formed. 



When one examines a specimen such as those in which Maxi- 

 mow, Dantschakoff and others have described the origin of 

 white and red cells from a common stem cell, it is impossible 

 to be absolutely certain that the two types of cells do arise from 

 the same individual stem cell. The stem mother cell is shown 

 within the mesenchyme, near this on the one side are various 

 early lymphocytes or leucocyte-like cells, and on the other side 

 are the various stages in erythroblast development. Each type 

 of cell graduates directly back to the stem mother cell or to a 

 mesenchymal cell. This much may be freely admitted, but to 

 say more is merely a matter of guess or interpretation. Since 

 it is absolutely impossible on fixed material to make the definite 

 statement that both of these two types of cells have arisen from 

 the one individual stem mother cell. The observer must 

 actually witness the stem mother cell divide into two cells, and 

 then observe one of these two cells either by differentiation or 

 continued division give rise to white corpuscles, and the other 

 either by differentiation or continued division give rise to erythro- 



