184 VICTOR E. EMMEL 



globin tends to remain enclosed in the cells in which it is first 

 formed, in mammals on the contrary, the mesenchymal cell differ- 

 entiating into the erythroblast, accumulates hemoglobin in its 

 cytoplasm, the nucleus assumes a more or less eccentric position, 

 physiological and structural changes ensue which result in the 

 initiation of a process which constricts off the mass of hemoglobin 

 containing cytoplasm, liberating it into the circulatory system 

 where it functions as a free non-nucleated red blood corpuscle. 

 The fact that the process is one of cytoplasmic constriction is 

 apparently more clearly evident in the case of the larger erythro- 

 blasts of the embryo where the nucleated remainder may include 

 a perceptible quantity of cytoplasm, as in the pig embryo, than in 

 the smaller erythroblasts of the adult organism where the process 

 may not be readily distinguishable from one of nuclear extrusion, 

 even though the two phenomena may be fundamentally different. 



SUMMARY AND CONCLUSIONS 



The observations and conclusions drawn from this study of the 

 erythrocytes of the pig embryo may be summarized as follows: 



1 . Certain cytological characteristics of the erythroblasts 



1. Morphological changes during cytomorphosis. 



During their differentiation the erythroblasts pass through a 

 series of successive transitional changes in which : 



a. The originally more or less spherical cell body changes to a 

 flattened biconcave disc or even a concavo-convex cup form, so 

 that in the pig embryo, in contrast to the usual descriptions for 

 mammals, the erythrocytes may assume the definitive form even 

 while still nucleated. 



Professor Shafer, and have interpreted the intra-cellular phenomena as instances 

 of atrophy rather than progressive differentiation. Shafer in 1913 reaffirms his 

 views and observes that "there is no improbability in supposing that in these 

 situations other cells than those which are bodily transformed, with extrusions or 

 atrophy of their nuclei, into erythrocytes, may share in the process of haemoglobin 

 formation, and the haemoglobin infiltrated cytoplasm may become budded off 

 from the cell from which it had been produced. Such budding off of colored cyto- 

 plasm from an endothelium cell of a blood vessel is depicted by Maximow in figure 

 569, c, and figure 571, c, p. 380. 



I 



