148 VICTOR E. EMMEL 



in which case the nucleus which has become separated from the 

 remainder of the cell in the formation of the non-nucleated eryth- 

 rocyte or plastid, instead of being free is still surrounded by an 

 appreciable quantity of adherent cytoplasm. These results sug- 

 gest the conclusion that just as in the case of the differentiation 

 of the lipoid containing membranes, so here too, the assumption 

 of an eccentric position by the nucleus is a gradual one correlated 

 with the formation of hemoglobin. That some of the processes 

 involved may in a manner be comparable to activities in se- 

 cretory cells, in which the new product tends to accumulate in one 

 part of the cell while the nucleus and part of the original cyto- 

 plasm is crowded toward the opposite pole of the cell. That 

 the hemoglobin differentiates presumably in a fluid or semifluid 

 form, while the lipoid substances of the cell accumulate at the sur- 

 face of the corpuscle, with the result that the remaining elements 

 of the original cytoplasm, which have not become involved in 

 the formation of hemoglobin, together with the nucleus have thus 

 come to occupy the periphery of the erythroblast in a manner pos- 

 sibly not unlike the conditions obtaining with regard to the ec- 

 centric position of the nuclei in certain active gland cells, or as 

 not infrequently occurs in various leucocytes at the height of 

 their specialized differentiation. It remains to be seen to what 

 extent this conclusion will be substantiated as the result of fur- 

 ther investigation. 



THE ORIGIN OF NON-NUCLEATED ERYTHROCYTES OR PLASTIDS 



1. STRUCTURAL CHARACTERISTICS OF THE NON-NUCLEATED 

 ERYTHROCYTES IN 10 TO 35 MM. PIG EMBRYOS 



The red blood elements of the 10 mm. pig are almost all nucle- 

 ated cells, although an occasional non-nucleated erythrocyte 

 may already be present. With the further growth of the em- 

 bryo from 10 to 25 mm. these non-nucleated erythrocytes grad- 

 ually increase in number. A little later, at various stages between 

 25 and 35 mm., this increase is greatly accelerated, so that in 

 embryos larger than 35 mm. or 40 mm., the blood, instead of 

 consisting chiefly of nucleated red cells is now composed largely, 



