CELLULAR ELEMENTS OF THE MAMMALIAN EMBRYO 101 



and the erythroblasts in the circulating blood (cf. figs. 37 and 38, 

 drawn with the same magnification). 



That the cytoplasm of the degenerating erythrocyte may be- 

 come vacuolated and assume a fighter stain is illustrated in 

 figures S7d and 34a. Similar degenerative erythrocytic changes 

 have also been described by Minot ('12) and may be observed 

 in tissue cultures (Emmel '14). Finally, attention has already 

 been directed to the fact that erythrocytes frequently escape 

 from the vascular channels into the adjacent embryonic tissue 

 spaces where they may eventually disintegrate, be ingested by 

 phagocytes, or possibly in some cases eliminated through the 

 lymphatic vessels as suggested by Minot ('12) for mammals and 

 as observed by Clark ('09) in the living tadpole. Cells which 

 can be unquestionably identified as such degenerating erythro- 

 cytes can be readily observed in the mesenchyma. The nuclei 

 may vary from round to highly irregular and lobulated forms 

 and the cytoplasm may be paler in stain reaction, vaculoated 

 and under certain conditions may even disappear. Among these 

 cells are such forms as are illustrated in figure 40 the nucleus of 

 which may still be identified as erythrocytic as seems clearly 

 indicated by the persistence of a thickened peripheral accumula- 

 tion of chromatin in a manner comparable to that of the circu- 

 latory erythrocytes shown in figures 37 and 34. Such a nuclear 

 structure is in decided contrast to that of the adjacent mesen- 

 chymal cells as may be seen in the same figures. Practically 

 all transitional stages can be found between such cells and those 

 shown in figure 38 representative of the so-called eosinophihc 

 leucocytes under discussion. It appears evident that such par- 

 tial hemolysis, cytoplasmic vacuolation and consequent periph- 

 eral disintegration in the erythrocytes which have escaped into 

 the mesenchyma may result in the production of cytoplasmic 

 processes of such a character as not to be readily distinguishable 

 from cellular processes of the adjacent mesenchymal cells with 

 which they appear to fuse. Such cells may present the decep- 

 tive appearance of differentiation in situ from mesenchymal 

 cells as indicated in figures 39 and 40. 



