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with Special Reference to the Activity of the Lium Hemopoiesis in the Mongoose Embryo

embryos, endothelium, origin, mm and theory

HEMOPOIESIS IN THE MONGOOSE EMBRYO, WITH SPECIAL REFERENCE TO THE ACTIVITY OF THE LIUM, INCLUDING THAT OF THE YOLK-SAC.

In several recent papers dealing with hemopoietic phenomena in turtle (7) and in pig embryos (s and 9) I described appearances on the basis of which I maintained a contributive role on the part of the endothelium, 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 Maximow 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 endothelium 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 endothelium 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 endothelial 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 1O-mm. pig embryo. (Enunel (4 and 5) ; Jordan (9).) Material AND METHODS.

The material includes three embryos, with yolk-sac attached, of 5, 6, and 7 mm. length. The embryos were collected in March 1912 at Montego Bay, Jamaica, British West Indies, while with the scientific expedition of the Department of Marine Biology of the Carnegie Institution of Washington, under the leadership of the Director, Dr. Alfred G. Mayer. The embryos were fixed in Helly's fluid, stained in toto with Delafield's hematoxylin, lightly counterstained with eosin, and sectioned in paraffin at 10 microns. From the viewpoint of hemo poietic phenomena the three embryos are practically identical. Since the 5 mm. embryo seems to possess a slight advantage in respect of abundance of crucial stages and of differential staining, the following description will pertain almost exclusively to this embryo. The tissue is perfectly normal, as is indicated by the abundant mitoses in prac tically every tissue. The cell-clusters of the aorta show a progressive increase in size and differentiation from the 5 to the 7 mm. embryo.