296 H. E. JORDAN 



That the giant cells have no genetic relationship to the ento- 

 derm, as urged by Graf. v. Spee (22), is certain. That the 

 method of nuclear multiplication is largely a matter of budding 

 and fission is also demonstrable (fig. 35). It may be stated also 

 that these cells are much more abundant at about the 10 mm. 

 than at earlier and later stages; and that while all the other 

 types of erythrocytes are found in the embryonic circulatory 

 system, giant cells are practically limited to the yolk-sac vessels. 

 A few smaller varieties appear in the liver and the mesonephroi, 

 and occasionally one appears in a capillary in the mesenchyma 

 next the brain. Haemoblasts also are only sparingly found 

 outside of the yolk-sac, liver, and the glomerular sinusoids of 

 the mesonephroi. The normoblasts are in the vast majority in 

 the intraembryonic circulatory system. 



On the basis of their occasional normoblast content the giant 

 cells might be interpreted 1) as erythrophages or 2) as multiple 

 erythroblasts. The latter interpretation was urged by Graf 

 V. Spee (22). The former interpretation is supported by the 

 fact that endothelial cells — which are potential haemoblasts — 

 may apparently function as phagocytes for erythroblasts. The 

 latter more plausible conclusion rests upon my observations 

 that in a giant cell with two normoblasts (fig. 26) no additional 

 nucleus is present; and the further fact that frequently the cell 

 membrane of the normoblast is not separated from the cytoplasm 

 of the giant cell by any space, but the two structures appear 

 continuous (fig. 26). Moreover in certain multinuclear giant 

 cells the several nuclei and their enveloping cytoplasmic areas 

 are at different stages of development. In figure 25 two of the 

 nuclei are typical haemoblast nuclei, two are typical erythroblast 

 nuclei. The upper right hand nucleus {x) is differentiated more 

 than the other, and the enveloping cytoplasm is beginning to 

 take on normoblast characteristics. Ne\'ertheless this inter- 

 pretation must perhaps still be regarded as more oi* less tentative. 

 But the fact that mega- and polykaryocytes are present in all 

 haemopoietic foci, embryonic, foetal and adult, strongly supports 

 the conclusion that they are closely associated with the haemo- 

 poietic process. As such, however, their function does not seem 



