288 H. E. JORDAN 



more delicate, sometimes double (fig. 23) and less deeply chro- 

 matic. The cytoplasm is slightly acidophilic. Both nuclear 

 and cytoplasmic features resemble those of the erythroblasts 

 ('megaloblasts'). 3) A cell of similar or even larger size with 

 numerous nuclei (as many as eight are common) of various shapes 

 and sizes and differing in structure between the two extremes 

 above described (figs. 11, 12 and 35). The cytoplasm of such a 

 cell is also more or less basophilic. 



The origin of giant cells can be definitely traced by means of 

 transition stages to the haemoblasts. Type 1, above described, 

 is simply a giant haemoblast (compare figs. 3 a, 7 and 33). Type 

 2 is a giant haemoblast with several nuclei (compare figs. 3 a 

 and 11) derived by nuclear amitotic division — occasionally 

 possibly also by nuclear mitosis — unaccompanied by cyto- 

 plasmic division. The cytoplasm has entered upon the early 

 stages of differentiation into erythroblast cytoplasm. Type 3 

 is derived from type 1 by extreme and irregular fission of the 

 single nucleus, accompanied by slight differentiation in the 

 cytoplasm (figs. 12, 25 and 35). 



Frequently a typical giant cell with two or even three nuclei 

 may be seen in continuity with the endothelial wall of the 

 blood vessel, and in late stages of separation (figs. 8 and 9). 

 This observation further supports the conclusion of haemoblast 

 derivation of giant cells. There is no evidence in favor of an 

 entodermal origin of giant cells as held by Graf. v. Spee (22) 

 in the case of the human yolk-sac. 



A small number of giant cells contain one or several normo- 

 blasts. The normoblast periphery may be separated from 

 the enveloping giant cell cytoplasm by a narrow space (fig. 10) ; 

 or such space may be lacking, in which event the continuity 

 between the two cytoplasms seems complete (fig. 26). Two 

 possibilities of the origin of these intracellular normoblasts at 

 once suggest themselves: 1) ingestion; 2) differentiation from 

 the nuclei and portions of the surrounding cytoplasm of the giant 

 cell. The fact that endothelial cells (potential haemoblasts) 

 may ingest erythroblasts (fig. 28), as above described, lends 

 much weight to the first suggestion. The further facts, how- 



