306 Papers from the Department of Marine Biology. 



my article on mongoose hemogenesis and attempt an incorporation of 

 this discussion in the body of a revised paper. A glance at our illus- 

 trations shows the essential identity of our observations; and this 

 point is emphasized by a comparison of our descriptions, after allow- 

 ance is made for differences in form and degree of development. Our 

 independent observations are in essential agreement, but our inter- 

 pretations are wide apart. The embryonic derivation of certain cel- 

 lular blood constituents from proliferating and metamorphosing endo- 

 thelium seems well established; as is also the origin of leucocyte-like 

 cells (macrophages?) in the serous fluids from the mesothelium of the 

 serous cavities. I incline to view the whole process as a normal hemo- 

 genic phenomenon. 



Emmel now adheres to a pathologic interpretation, concluding that, 

 while vascular endothelium may not under normal conditions give 

 rise to cellular elements of the blood, "it appears that in both embryo 

 and adult mammals, endothelial tissue ordinarily passive may under 

 certain abnormal conditions, however, assume proliferative activities 

 contributing to the free cellular elements of the circulating blood"; 

 also that "the participation of the mesothelium in the origin of macro- 

 phages in the embryonic ccelom is not improbably also a reaction to 

 stimulative conditions arising in part at least through degeneration 

 and disintergration of erythrocytes and other foreign elements escaping 

 into these cavities." 



Emmel evidently labors under a feeling of compulsion to interpret 

 his findings in harmony with the original angioblast theory, which 

 denies participation of the vascular endothelium in the normal process 

 of the formation of cellular elements of the blood. It may be quite 

 true that abnormal conditions of various sorts, experimental or patho- 

 logic, may stimulate the endothelium to proliferative activity, but 

 recognition of this fact does not compel interpretation of all endothelial 

 proliferative activity in terms of abnormal conditions. 



That certain abnormal conditions do stimulate endothelium to pro- 

 liferation and desquamation and a coincident differentiation proves 

 only that endothelium carries the inherent capacity to thus behave. 

 Similar behavior under early embryonic conditions may be a perfectly 

 normal process. This similarity between a normal embryonic process 

 and an abnormal later condition may be simply an aspect of a very 

 widespread phenomenon in which a pathologic adult condition is an 

 abnormally reawakened normal embryonic condition, e. g., developing 

 cardiac muscle and hypertrophying cardiac muscle, etc. A leiomyoma 

 arises apparently as the result of a normal differentiation of smooth 

 muscle-cells in an abnormal degree. Tumor cells are generally believed 

 to be biologically of the same nature as normal cells. The cell-clusters 

 above described would, if increased and enlarged to an abnormal de- 

 gree, produce a condition comparable to a hemangio-endothelioblastoma. 



