186 VICTOR E. EMMEL 



the erythrocyte previous to the formation of the non-nucleated 

 corpuscle. 



c. An explanation of the assumption of an eccentric position 

 on the part of the nucleus is suggested on the basis of the differen- 

 tiation of a hemoglobin content tending to accumulate at one sicie 

 of the cell and displacing the nucleus and the remainder of the 

 original cytoplasm toward the opposite pole, a conclusion appar- 

 ently supported by the character of the reaction of the erythro- 

 blast to osmotic changes and the occurrence in the circulation of 

 free erythrocytic nuclei surrounded by a rim of cytoplasm, as 

 indicative of structural differences between the nuclear and cyto- 

 plasmic poles of the cell. 



2. The origin of non-nucleated erythrocytes or plastids 



1. Structural characteristics: 



a. In size the non-nucleated erythrocytes or plastids may vary 

 from large plastids approximating the dimensions of the large 

 erythroblasts, to smaller forms the size of blood platelets. 



b. In form they vary from rounded or spherical to the definitive 

 biconcave discs and concavo-convex or cup-shaped elements, the 

 definitive forms predominating. 



c. An occasional plastid may have a small, tapering cytoplasmic 

 process projecting from its surface. 



2. The origin of non-nucleated erythrocytes in blood cultures: 



a. Autoplastic cultures were studied from pig embryos at a stage 

 in which the formation of plastids in the circulating blood is at its 

 height, but no conclusive evidence was obtained indicating 

 the origin of plastids by the extrusion of the nucleus from the 

 erythroblasts or of its disintegration within the cell. 



b. On the contrary, a process was repeatedly observed and 

 studied in which there occurred a constriction of the cytoplasm 

 in the region between the nuclear and cytoplasmic poles of the 

 erythroblast, which, when completed, resulted in the division of 

 the cell into two parts, the one a nucleated structure, the other a 

 non-nucleated hemoglobin containing corpuscle. 



