ERYTHROBLASTS IN THE PIG EMBRYO 185 



b. The nuclei, in correlation with these changes in cell form, 

 decrease in size and become structurally compact, assume a more 

 or less eccentric position at one side of the cell, designated in this 

 description as the nuclear pole in contrast to the opposite or cyto- 

 plasmic pole, and manifest a tendency toward a flattening in 

 conformity with the shape of the cell body. 



2. Cytoplasmic processes: 



a. Not infrequently an erythroblast is encountered character- 

 ized by a small, pointed, cytoplasmic process projecting from the 

 surface of the cell. 



6. Observations were described indicating: first, that these proc- 

 esses are normally present in the embryo, and second, that they 

 may be primarily due to certain conditions attending the final 

 separation of the two daughter cells during mitotic division. 



3. Orientation with reference to gravity: 



It was discovered that freely suspended mature erythroblasts 

 having eccentrically located nuclei tend to adjust themselves in 

 such a manner with reference to gravity that the nuclear pole of 

 the cell swings undermost. 



4. Reaction to osmotic changes : 



Under certain changed osmotic conditions such as an increase 

 in the percentage of water in the plasma, instead of the ensuing 

 swelUng reaction in the disc shaped erythroblast being equal 

 throughout the cell body, the cytoplasmic pole of the disc becomes 

 swollen and approaches a spherical shape, while the nuclear pole 

 of the corpuscle may undergo but little if any modification. 



5. Bearing of these observations upon certain problems in the 

 cytomorphosis of the mammalian erythrocyte: 



a. From the preceding data it seems clearly evident that in 

 contrast to the rather generally accepted view, the assumption 

 of the definitive form of the erythrocyte is not necessarily initiated 

 by or dependent upon an extrusion of the nucleus. 



b. That on the contrary, a substantial body of facts supports the 

 conclusion that correlated with the hemoglobin formation is the 

 differentiation of a lipoid containing membrane which, as an im- 

 portant factor in producing a flattening of the cell, manifests itself 

 in the pig embryo in the assumption of the definitive form of 



