CELLULAR ELEMENTS OF THE MAMMALIAN EMBRYO 109 



sistence in the adult mammal of the potentiality on the part of 

 the mesothelium of contributing, under certain stimulating en- 

 vironmental conditions, liberated cellular elements to the body 

 cavities in a manner comparable to the processes taking place 

 in the embryonic coelom. 



VII. RESUMfi 



1. A considerable number of free cellular elements were found 

 to be more or less constantly present in the coelomic cavities of 

 pig, rabbit and mouse embryos. 



2. These coelomic elements may be described as falling into 

 two groups, the one consisting of basophilic staining and usually 

 phagocytically active cells and the other of cellular elements 

 characterized by their eosinophilic staining qualities and non- 

 phagocytic activity. 



3. The coelomic macrophags 



a. The basophihc cells may be conveniently further subdivided 

 into the following types: 1) cells relatively smaller and more 

 spherical in form, containing an occasional small cytoplasmic 

 vacuole and a rather dark staining, round or kidney shaped 

 nucleus; 2) cells usually larger in size, more oval or irregular in 

 form, containing one or more phagocytic inclusions, having a 

 round or kidney shaped and more or less eccentrically situated 

 nucleus and the cytoplasm and nucleoplasm of which take a 

 considerably lighter basophihc stain; 3) cells characterized by 

 the vaculoated condition of the cytoplasm and the not infre- 

 quent occurrence of cytoplasmic processes or buds projecting 

 from the surface of the cell. 



6. The transitional stages which may be found between these 

 different cells are of such a character as to justify correlating 

 their size, form, nuclear, and cytoplasmic differences with varia- 

 tions in differentiation and function. Consequently practically 

 all of these cells are here regarded as belonging to a common 

 group which in view of their evident phagocytic functions may 

 be designated as coelomic macrophags. 



c. As to the origin of these coelomic macrophags, some of 

 them may no doubt have entered the coelomic cavities from 



