ERYTHROBLASTS IN THE PIC EMBRYO 133 



appeared somewhat larger in diameter after than before fixation: 

 ''Im Deckglastrock enpriiparat erscheinen also die Zellen grosser 

 als bei frischer Untersuchung, was wohl darin seinen Grund hat, 

 dass im angetrockneten Priiparate die kughge Zelle durch die 

 niedrige, angetrocknete Plasmaschicht fiacher, dafiir aber breiter 

 wird" (page 39). 



The results of these observations seem to leave no other alter- 

 native but the conclusion that the typical norrnal form of the 

 majority of the erythroblasts in the blood of the 25 mm -35 mm. pig 

 embryo, instead of being spherical, are biconcave-disced and cup- 

 shaped in form. 



Younger pig embryos. Younger embryos were next studied to 

 ascertain transitional stages in the assumption of this form. The 

 material consisted of both fresh and fixed blood, foetal membranes, 

 serial celloidin and paraffine sections, fixation and staining meth- 

 ods being the same as in the previous preparations. 



The youngest embryos obtained measured 3 mm. in greatest 

 length. The primitive blood cells (mesamoeboids of Minot '12), 

 and progenitors of the red blood cells as they lie free in the vessels 

 of the embryo and the vascular network of the foetal membranes 

 are uniformly spherical in form (fig. 1 eu). With Giemsa the 

 cytoplasm takes a basophilic stain and as yet there is little if any 

 evidence of the formation of hemoglobin. Younger blood cells in 

 the blood islands of the yolk sac are more irregular in form, prob- 

 ably due in part to a not yet complete rounding up of the newly 

 liberated primitive blood cells. 



In 7 to 8 mm. embryos the early red blood cells are now be- 

 coming characterized by the presence of a small amount of hemo- 

 globin, as indicated by the reddish tinge of the stained cytoplasm. 

 In fresh preparations the living cytoplasm appears a very light 

 yellow in color. "V^Tiile the majority of these red blood cells or 

 primitive erythroblasts are more or less spherical in form, many 

 of them now begin to show a definite biconvex lens shape (fig. 2, 

 ep). These observations from serial sections and membranes 

 mounted in toto were also verified in the study of fresh prepara- 

 tions, in which case the entire embryo with part of its membranes 

 could be placed under a cover-glass upon the slide, sealed with 



