CELLULAR ELEMENTS OF THE MAMMALIAN EMBRYO 99 



2. Degenerating erythrohlasts and the so-called eosinophilic 

 leucocytes in einhryonic mesenchyma 



Attention has already been directed to the fact that upon 

 first impression certain characteristics of the eosin staining coe- 

 loniic cells were suggestive of leucocytic elements but that the 

 results of subsequent investigation indicated the nature of these 

 cells to be that of degenerating erythrocytes. In the case of the 

 rabbit eosinophilic leucocytes are also absent in the serous cavi-, 

 ties of the adult (Weidenreich, '12, p. 127). In connection with 

 this conclusion it is to be taken into account, however, that cells 

 which appear practically identical in both nuclear and cyto- 

 plasmic structure with these degenerating erythrocytes in the 

 coelomic cavities are also found in the intercellular spaces of 

 the mesenchyma of the same embryos (figs. 38 to 40), concern- 

 ing the nature of which Maximow ('09) in his description of the 

 7 mm. cat embryo reaches the theoretically important- conclu- 

 sion that they are eosinophilic leucocytes differentiating in situ 

 from mesenchymal cells. 



The apparent identity of these cellular elements of the mesen- 

 chyma, both as described by Maximow and as observed in the 

 present material, with the cells interpreted as degenerating 

 erythrocytes in the coelomic cavities has rendered it necessary to 

 reexamine the evidence concerning the nature of the cellular 

 structures in the mesencyhma. In presenting the results of 

 such a study it may be stated that the following considerations 

 have led to a negative conclusion as to the leucocytic character 

 of the cellular elements in question in the mesenchyma. In 

 the first instance it is to be observed that no special eosinophihc 

 granulation can be demonstrated in these cells (figs. 38 to 40). 

 Indeed Maximow himself, although maintaining that in the 

 mesenchymal wandering cell the nucleus becomes lobulated into 

 a number of subdivisions held together in some cases by only 

 fine connecting strands, is nevertheless obliged to admit that no 

 leucocytic granules can be recognized in the cytoplasm of the 

 cells here in question (p. 525). In explanation of this, Maxi- 

 mow points out that it is likewise also very difficult to demon- 



