146 VICTOR E. EMMEL 



out that since it has been shown that the cell may approximate the 

 definitive form while still nucleated, it follows that an active lipoid 

 membrane may already be present in the nucleated erythroblast. 

 In view of these facts the conclusion presents itself that the differ- 

 entiation of an effective lipoid membrane is not a matter of sudden 

 formation, as intimated by Albrecht, but rather that it is gradually 

 differentiated along with the formation of hemoglobin during the 

 cytomorphosis of the cell, and that under certain conditions, as 

 in the case of the large erythroblasts of the pig embryo, this differ- 

 entiation may manifest itseff by the gradual modification of the 

 form of the erythroblast in the direction of a biconcave disc or 

 cup shape even before the cell has given rise to a non-nucleated 

 plastid. It is of course not to be overlooked that other factors 

 such as the loss of water (Malassez '82, p. 22), an increase in the 

 concentration of the blood plasma (Kolliker '46, p. 142), and var- 

 iations in chemical composition such as the quantity of CO2 

 (Hamburger '97, '02), may participate in the process. In con- 

 nection with this conclusion of the gradual formation of a form 

 determining membrane during cytomorphosis, it is of interest 

 to note the conclusion of Minot ('12), that the "cell membranes 

 probably developed at the same time as the hemoglobin" (p. 505), 

 and that of Weidenreich ('05), that in the differentiation of the 

 young, nucleated erythrocyte " die Membran durch eine einfache 

 Ablagerung des Lezithins und Cholestearins, die ihre wesent- 

 lichen Bestandteile sind, in der aussersten Peripherie der homo- 

 genen Blutzelle zustande Kommt" (p. 444). 



b. Possible factors accounting for the eccentric position of the 

 nucleus in the erythroblast 



Several explanations have been advanced for the change in 

 position of the erythrocytic nucleus from the center toward the 

 periphery of the cell during differentiation. Weidenreich ('05, 

 p. 434), suggests that with the liquefaction of the hemoglobin 

 containing cytoplasm, the nucleus may become relatively lighter 

 in specific gravity and, being free, float toward the surface of the 

 corpuscle. Jolly ('07, p. 273), while recognizing the possibility 



