CELU'LAU ELEMENTS OF THE MAMMALIAN EMBRYO // 



free cells of the coelomic Ciivities belong to this second class. 

 Cells of the third type are illustrated in figures 14 van. and 13. 

 The chief characteristic is that of the highly vacuolated condi- 

 tion of the cytoplasm. The rounded or flattened nucleus is 

 eccentric in position. Not infrequently^ cytoplasmic knobs or 

 buds are observed projecting from the surface of the cell (figs. 

 14 and 44). These cytoplasmic buds may vary considerably in 

 intensity of stain but in all the cases observed they were 

 basophilic in their stain reaction. The relation of some of 

 these buds as partially if not entirely detached from the cell 

 (fig. 446), together with the occasional occurrence of apparently 

 similar basophilic bodies free in the coelomic fluid, indicates 

 the possible constriction ofT of these cytoplasmic processes from 

 the parent cell. If such is the case the phenomenon appears 

 comparable to the liberation of detached portions of the cyto- 

 plasm as described by Weidenreich, '12, p. 2602 (also Downey 

 and Weidenreich, '12, and Downey, '12). 



The question now arises as to whether these cell types repre- 

 sent genetically distinct kinds of cells or whether these cells are 

 more or less closely interrelated structurally and functionally. 

 In attempting to answer this question from sectioned material, 

 we are necessarily largely dependent upon such evidence as can 

 be obtained by a comparative cytological study, and endeavor- 

 ing to ascertain the occurrence or absence of data indicati^-e of 

 structural intergradations between the cells in question. In 

 the course of such a study the following results were attained. 

 Attention has already been directed to the fact that a chief dis- 

 tinguishing characteristic of the second type of cells is that of 

 the phagocytic ingestion of other cell bodies. In comparing 

 cells icm and pcm in figure 14 as representative of the first two 

 groups just described, a considerable size difTerence is at once 

 evident. It may be questioned, however, whether this is not 

 largely a result of functional activities. The ingestion of cell 

 bodies may be expected to increase the cell size and this is what 

 is actually found, for the coelomic macrophags containing 

 three, four or more cellular inclusions are larger than those hav- 

 ing only a single inclusion, as may be observed for example in 



