294 CHARLES R. STOCKARD 



of the trout and this is thought to represent the conjoined car- 

 dinal veins. We have noticed that in Fundulus the intermediate 

 cell mass is sometimes divided forming two lateral cardinals 

 loaded with blood cells, while generally it exhibits a median un- 

 paired condition. In the pelagic forms the vessels are all hol- 

 low at the time of hatching and the blood cells have not appeared. 



Derjugin ('02) claims from a study of the pelagic egg of Lophius 

 that the vessel cells of the aorta and cardinals are derived from 

 the sclerotom. Felix ('97) like Ziegler ('87) differs with Swaen 

 and Brachet ('01, '04) in that he derives the aorta not from the 

 "Venenstrang" but from the sclerotom which under the noto- 

 chord forms a mesenchymal aortic string. Felix states that no 

 blood cells are to be seen in the aortic anlage, while the cardinal 

 veins, of course, are loaded with the blood cells of the inter- 

 mediate cell mass. Felix, therefore, derives the two chief ves- 

 sels of the embryo from two different parts of the mesoderm, 

 ,the somites or sclerotoms and the lateral plates. 



Sobotta ('02) terms the intermediate cell mass "Blutstrange" 

 and derives it from the lateral plate, though he had earlier claimed 

 it to arise from the somites. He described it in the trout embryo 

 in the region from the eighth to the thirty-third somite. The 

 'Blutstrange' at first paired, are naked cellular strings without a 

 true vessel covering. This they receive later as the cardinal 

 vein anlagen. The endothelial cells of the cardinal veins he 

 derives from the same source which produces the aorta, namely, 

 the sclerotoms. 



Finally, then, Swaen and Brachet derive the blood and vascu- 

 lar endothehum of the aorta and venae cardinales from the inter- 

 mediate cell mass which arises from the lateral plate. Felix 

 derives only the blood and vascular endothehum of the cardinals 

 from the intermediate cell mass which is separated originally 

 from the lateral plate. The aortic endothelium arises from the 

 sclerotoms. Sobotta considers the intermediate cell mass an 

 exclusive blood forming material, while all vascular endothelium, 

 including the heart, is derived from the sclerotoms which are 

 budded off froni the somite system. This disagreement, as 

 we have pointed out before, is not of primary importance and 



