ORIGIN OF BLOOD AND ENDOTHELIUM 265 



tions one finds here only red blood corpuscles. In other words, 

 this chief stem blood anlage of the bony fish seems to be a specific 

 red blood cell forming mass. This mass was first discovered by 

 Oellacher in 1873 and has been shown by numerous investigators, 

 Zeigler ('87), Winckebach ('86), Henneguy ('88), Sobotta ('94), 

 Felix ('97), Swaen and Brachet ('99-'01) and others, to be pecu- 

 liar to the Teleosts. 



It is important to know that none of these investigators have 

 yet recorded any type of blood cell arising from this mass other 

 than the erythroblast. Of course, it may be argued that no 

 special study was made of this particular point. Yet it is cer- 

 tainly true that if lymphocytes or leucocytes had been present 

 to any extent, they should have been observed by many of these 

 very capable and careful workers. It has recently been claimed 

 by Maximow ('09), Dantschakoff ('07, '08) and others, that the 

 popular opinion that leucocytes are very late in arising is erro- 

 neous since they actually arise just as early as the erythroblast. 

 Then it seems all the more probable that if lymphocytes or 

 leucocytes had been present in this intermediate cell mass such 

 cells would have been discovered, since the mass has been care- 

 fully investigated right up to the moment at which it becomes 

 swept into the circulating plasma. 



Various investigators have differed as to the vascular products 

 derived from the intermediate cell mass. Some have claimed 

 that it forms only blood cells and no vascular endothelium, 

 Sobotta ('02), while others have attributed the production of 

 cardinal veins or venous endothelium as well as the blood cells 

 to this mass, Fehx ('97), and finally others, Swaen and Brachet 

 ('01, '04) in particular, have considered this to be the source 

 of both the aorta and cardinal veins as well as the red blood cells. 

 I have spent considerable time in a study of this question and 

 am inclined to believe that the endothelium of the cardinal veins 

 and aorta arises from the mesenchymal cells surrounding the 

 intermediate cell mass, which are different in nature from the 

 cells actually constituting the mass. Yet it must be admitted 

 that up to the present moment a complete demonstration of the 

 origin of aortic endothelium from the cells about the periphery 



