ERYTHROBLASTS IN THE PIG EMBRYO 129 



CERTAIN CYTOLOGICAL CHARACTERISTICS OF THE ERYTHRO- 

 BLASTS PREVIOUS TO THE FORMATION OF THE NON-NUCLEATED 

 ERYTHROCYTES OR PLASTIDS 



1. MORPHOLOGICAL CHANGES DURING CYTOMORPHOSIS 



a. Form changes in the cell body 



25 to 35 mm. pig embryos. Engel ('99), whose work represents 

 perhaps the most extensive study, so far, of the blood of the young 

 pig embryo, in describing the form of the typical large nucleated 

 erythroblast (metrocytes II) of the 35 mm. pig, states that 'die 

 Zellform ist kugelig' (p. 41). In the development of the nu- 

 cleated red cells he distinguishes between the somewhat smaller 

 erythroblasts with a larger nucleus and relatively smaller amount 

 of cytoplasm which he designated as 'metrocyte I', and the more 

 highly differentiated red blood cell larger in size, richer in hemo- 

 globin, with a smaller, more compact nucleus, designated as 

 'metrocyte II.' Throughout the account, however, there is no 

 indication that the typical normal form of these nucleated red 

 cells is regarded as anything but rounded or spherical throughout 

 their cytomorphosis, that is, up to the stage of their transfor- 

 mation into the non-nucleated forms. 



The methods employed by Engel consisted in making cover 

 glass preparations of the blood taken directly from the heart, liver, 

 and other organs of the embryos as they were obtained fresh at 

 the abattoir. After drying part of the preparations in the air 

 and immersing the others in various fixing fluids, they were then 

 transferred to his laboratory and stained. In the present inves- 

 tigation, the material first studied consisted of blood taken di- 

 rectly from the embryonic heart in the following manner: the 

 pregnant uteri were either opened at once at the abattoir or 

 conveyed to the laboratory, the transference in the latter case 

 being made in a closed apparatus built on the principle of the fire- 

 less cooker, in which the material could be kept at the normal 

 temperature of about 38° . After exposing the embryo the umbilical 

 cord was clamped with a small serrefine artery clamp, the cord 

 was then cut, the embryo removed from the uterus, and im- 

 mediately placed in a warm chamber. The heart -was then ex- 



