110 V. E. EMMEL 



extra coelomic regions, but the present results do not indicate 

 this to be the only source of origin of these cells. On the con- 

 trary the observation that at the surface of the coelomic walls, 

 in the free mesothelial cell masses, and the pleuro-pericardial 

 and pleuro-peritoneal membranes, mesothelial cells are found 

 which are rounded in form, manifest phagocytic characteristics 

 apparently identical with that of the typical macrophags, and 

 the evidence advanced that these cells may become detached as 

 free cells, support the conclusion that the coelomic mesothelium 

 is an important source of origin for the phagocytic cells found in 

 the embryonic coelom. 



4, Erythrocytic elements in the coelomic cavities. 



a. The second of the two groups of coelomic cellular elements 

 above indicated again fall into two sub-groups, the one consist- 

 ing of small non-nucleated bodies and the other of larger nucleated 

 cells. 



h. The present data indicate these structures to be erythro- 

 cytic in nature; the larger nucleated cells representing degen- 

 erating nucleated red blood corpuscles and the smaller eosin 

 staining bodies consisting chiefly of degenerating erythrocytic 

 nuclei. 



5. Erj^throcytic disintegration in the mesenchyma. 



a. In the embryonic mesenchyma there occur small eosin 

 staining bodies which have been interpreted as hemoglobin 

 containing secretion products of mesenchymal cells (Maximow). 

 But on the basis of the present evidence concerning their dis- 

 tribution, structure and close cytological correspondence to disin- 

 tegrating erythrocytes as observed in the circulating blood, inter- 

 cellular tissue spaces and phagocytic inclusions and to eryth- 

 rocytic nuclei persisting after the formation of non-nucleated 

 erythrocytes, the conclusion is drawn that the bodies in question 

 represent chiefly erythrocytic elements consisting of degenerat- 

 ing and in many cases phagocytically ingested erythroblasts 

 and, in older embryos, including nucleated erythrocytic bodies 

 arising in connection with the formation of erythro-plastids or 

 non-nucleated erythrocytes, rather than the products of mesen- 

 chymal secretory activities. 



