136 VICTOR E. EMMEL 



Concerning these results it may be observed that for the 

 various types of tissue cells in the organism there is, with cer- 

 tain exceptions, a general relationship between the cell body 

 and nucleus, such that the latter tends to conform to the former 

 in shape. In view of this fact, this tendency toward a flattening of 

 the erythrocytic nucleus in the pig embryo appears important as 

 a further confirmation of the conclusion that the fully differentiat- 

 ed erythroblast normally tends to assume a biconcave disc or cup 

 shape, for it is not readily evident how such a correlation in 

 these two structures could be the result of any artificial or abnor- 

 mal conditions of manipulation or fixation. It is not without in- 

 terest also to note further that for lower vertebrates, in which 

 the definitive erythrocytes are permanently nucleated, a similar 

 flattening of erythrocytic nuclei in conformity with the lens or 

 disc shaped cells has been recorded by Rawitz COO), for certain 

 ganoids and teleosts, by Giglio-Tos ('97), for amphibia, and by 

 Pouchet (79) for triton. 



In conclusion, then, concerning changes in the form of the 

 nucleated red blood corpuscles in 3 to 35 mm. pig embryos, it 

 appears evident that during their ajtomorphosis the erythroblasts 

 normally pass through a series of successive transitional changes 

 from a spherical to a biconcave disc or even concave-convex bell 

 form, accompanied by nuclear changes, which include a decrease in 

 size, and assumption of a more or less eccentric position, and a 

 tendency toward a flattening in conformity with the shape of the cell 

 body. 



c. Discussion concerning the occurrence of similar changes in 

 other mammals 



In generally accepted accounts of the blood cells of the mam- 

 malian embryo, the normal form of the erythroblast is described 

 as typically rounded or spherical. There is, however, some ground 

 for questioning whether it is not necessary to determine to what 

 extent this conclusion is to be regarded valid, for there is consid- 

 erable evidence indicating the assumption of a disc or cup shaped 

 by nucleated erythrocytes in a number of different animals. 



