PLATE 2 



EXPLANATION OF FIGURES 



14 One of fourteen sections through the pleuro-pericardial membrane of a 

 7 mm. pig embryo, c, represents a central issue core surrounded by mesothelial 

 cells (mes). Many of these cells have assumed a rounded form and are partially 

 if not entirely detached from the main mass. These modified cells are phago- 

 cytically active (pcm), contain cytoplasmic vacuoles (vcm) and present struc- 

 tural and tinctorial characters practically identical with that of typical macro- 

 phags. For general relations see figure 43. e. small eosin staining bodies (cf. 

 figs. 20 to 26). 



15 Free mesothelial cell masses in the pericardial cavitj^ of a 9 mm. rabbit 

 embryo. The visceral and parietal pericardial walls, respective!}', are at the 

 right and left sides of the figure {mes). 



16 Free mesothelial cell mass in the ventral region of the pericardial cavity 

 of a 7 mm. pig embryo. It extends through five sections, but in both this case 

 as well as in figure 15 these cellular masses are at no point attached to the coelomic 

 wall. Some of the mesothelial cells are partially detached, present a rounded 

 form and a slightly more basophilic stain reaction (/«). 



17 A region of the mesothelial surface showing a rounded, partially detached 

 basophilic cell (tn) which appears to be a modified mesothelial cell. Visceral 

 pericardium of a 9 mm. pig embryo (cf. figs. 41, 43, 44). 



18 A group of free cells in the peritoneal cavity of a 9 mm. rabbit embryo, 

 interpreted in the text as degenerating erythrocytes. In some of the cells indi- 

 cations of hemoglobin are still evident (a), in others the cytoplasm is paler in 

 color show cytoplasmic vacuolation and degenerative nuclear changes (b, c). 



19 Other instances of degenerative nuclear and cytoplasmic changes in 

 erythrocytes (cf. fig. 18). Peritoneal cavity, 9 mm. rabbit embryo. 



ABBREVIATIONS 



cm, coelomic macrophags mc, mesenchymal cells 



(/, mitotic figures mes, mesothelium 



icm, coelomic macrophags. apparently 7)un, mesothelial cell masses found free 



in a stage of inactivity with refer- in the coelomic cavities 



ence to phagocytic functions pcv, pericardial cavity 



in, phagocytic inclusions pcm, coelomic macrophags in a stage 



7u, rounded cells interpreted as meso- of active phagocytosis 



thelial cells in the process of beconi- vcm, vacuolated coelomic macrophags 



ing detached as free cells in the coe- to, vessel wall 



lomic activities 



118 



