HEMOPOIESIS IN THE MONGOOSE EMBRYO, WITH SPECIAL 

 REFERENCE TO THE ACTIVITY OF THE ENDOTHE- 

 LIUM, INCLUDING THAT OF THE YOLK-SAC. 



By H. E. Jordan. 



INTRODUCTION. 



In several recent papers dealing with hemopoietic phenomena in 

 turtle (7) and in pig embryos (8 and 9) I described appearances on the 

 basis of which I maintained a contributive role on the part of the 

 endothehum, both intraembryonic and yolk-sac. This position is in 

 agreement with that of Schridde (20), Maximow (11 and 12), and others 

 who have studied the origin and development of blood-cells in various 

 forms. Principally in the work of Maxiniow and of Dantschakoff (3) 

 this method of partial blood-cell origin has become related to the mono- 

 phyletic theory of hemogenesis which they support. On the basis of 

 his experimental work with Fundulus embryos, narcotized with alcohol, 

 Stockard (21) concludes that the endothelium in these embryos can not 

 transform into hemoblasts; and he views with skepticism the whole 

 mass of morphologic evidence offered in proof of the hemogenic capac- 

 ity of endothelium, claiming that a different interpretation of descrip- 

 tions and illustrations is at least as plausible as the one usually given. 

 Stockard, moreover, attacks the monophyletic theory, and in the devel- 

 opment of his argument brings the non-hemogenic role of endothehum 

 into relation with the polyphyletic theory of blood-cell origin. More- 

 over, those who believe in the strict specificity of endothelium, and in 

 a degree those who accept the angioblast theory of His, dispute the 

 possibility of endothehum to give origin to blood-cells. It is the 

 chief purpose of this contribution to state and illustrate the evidence 

 which in the opinion of the author justifies a belief in the endothehal 

 origin of some hemoblasts and which agrees to a considerable extent 

 with a monophyletic interpretation of hemopoiesis. This study confines 

 itself largely to the mongoose embryo. No special virtue is claimed 

 for this form in this regard. The chief value of this material lies in 

 the fact of a superb fixation and a favorable staining, and in that it 

 is of a stage of development (5 to 7 mm.) where the phases in question 

 are especially abundant and clear. Moreover, it serves well as a key 

 to the proper interpretation of certain aortic cell-clusters described for 

 the 10-mm. pig embryo. (Emmel (4 and 5) ; Jordan (9).) 



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