UMBILICAL CORD OF THE PIG 13 



The method of erythrocytogenesis here described for this 

 specimen of umbilical cord of the pig, however, differs radically 

 from that described by Ranvier and Schaefer, in that the erythro- 

 plastid in this case differentiates from a nucleated portion of a 

 vasofactive cell (figs. 6, e; 15, b and e, and 14). That is, the 

 erythroplastid differentiates from a typical erythroblast in the 

 usual mode. The nucleus of the erythrocyte disappears by 

 karyolysis (fig. 15, e). This is apparently a very rapid process, 

 since it can be detected in only relatively few cells. If one 

 considered only cells like those of figures 12 and 13, the process 

 would appear to be identical with that described by Ranvier 

 and Schaefer; but figures 15, b, e, h, and/ demonstrate the essen- 

 tial difference. 



Certain investigators (Spulef, 12 Fuchs, 3 et al.) have expressed 

 dissent from Ranvier's and from Schaefer's interpretation of 

 their observations; they explain these phenomena, the occurrence 

 of which they confirm, in terms of regressive changes and phago- 

 cytosis. They believe that the so-called Vasoformative cells' 

 are either isolated portions of a disintegrating embryonic vas- 

 cular plexus or erythrophagic connective tissue cells. It is 

 obvious that since the vasofactive phenomena here described 

 for the umbilical cord of the pig are fundamentally different, 

 while superficially apparently identical with those described by 

 Ranvier and Schaefer, the criticisms of Spuler and Fuchs have 

 no pertinancy to this case. Moreover, the red cells involved in 

 this process in the umbilical cord of the pig show no distinct 

 nuclear or cytoplasmic marks of degeneration. This cord, except 

 for the almost complete absence of mitotic figures, appears in 

 perfectly healthy condition. No free erythrocytes are available 

 for phagocytosis in the regions here described. There is no 

 indication of a disintegration of blood-vessels; on the contrary, 

 the full-term cord is relatively more extensively vascularized 

 than the cord of the 21-mm. fetus. Finally, and most signifi- 

 cantly, this intracellular mode of erythrocytogenesis is strictly 

 comparable to that described for other hemopoietic organs, e.g., 

 yolk-sac of 10-mm. pig embryo, 5 yolk-sac of mongoose embryos, 6 

 and red bone-marrow. 7 



