In the following account the coelomic cellular elements found 

 in the present material may, on the basis of their cytological 

 and functional characteristics, be conveniently described as fall- 

 ing into two groups: first, the basophilic staining and usually 

 phagocytically active cells, which, as will become more evident 

 in the ensuing description, may be designated as the coelomic 

 macrophags; and second, cellular elements characterized by their 

 eosinophilic staining qualities and nonphagocytic activity. 



III. THE COELOMIC MACROPHAGS 



1. Cytological characteristics 



The majority of the free coelomic elements are embraced in 

 the first of the above indicated groups. These basophilic cells 

 may be further roughly subdivided into three t^^Des which may 

 be described as follows: 



The first of these types is illustrated in figures 1, 2, 9 and 14 

 icm. These cells are more or less spherical in form and some- 

 what smaller in size than those of the other two types. The 

 nucleus varies from a central to an eccentric position within the 

 cell, and may be either round or more or less indented on one 

 side, so as to approximate a kidney shape. The cytoplasm is 

 typically basophilic in staining reaction, is without any specific 

 granular structure and may occasionally contain several small 

 vacuoles. In form, size, nuclear and cytoplasmic structure these 

 cells appear comparable to certain phagocytic cells occurring 

 in the embryonic circulation of the same embryos. The cells of 

 the second type are illustrated in figures 4, 5, 6, 8b, 10, 14 pern. 

 They are as a rule larger in size and more oval or irregular in 

 contour. The nuclei are quite eccentric in position and as a 

 rule more flattened and kidney shaped in form. The cytoplasm 

 usually takes a much lighter basophilic stain. A distinguishing 

 characteristic is the phagocytic inclusions contained in the cyto- 

 plasm. These inclusions consist almost entirely of nuclei and 

 cell bodies at various stages of intracellular digestion. It is of 

 interest to note that these inclusions consist largely of red stain- 

 ing or apparently erythrocytic elements. The majority of the 



