118 FKANKLIN P. REAGAN 



thelial cells with these latter derivatives as being equally specific 

 with pancreatic cells and liver cells (65, p. 323). He assures 

 us that an invisible destiny shapes the ends of pre-endothelial 

 cells, yet on page 316 (65) he states that the mesenchyme ''may 

 be admitted to form endothelium largely as a response to physi- 

 cal conditions." He states that erythroblasts never divide when 

 inside an endoth'^lial cavity, and that red blood cells are always 

 formed in or budded into a vascular space; both these statements 

 are probably incorrect. 



There are some interesting conditions in Stockard's own ma- 

 terial which he seems to have misinterpreted. Let us examine 

 first his basis of belief that no anterior vessel ever contains a red 

 blood cell if the blood never circulates. We must first agree on 

 what is meant by, and included among the anterior vessels. 

 Doubtless the pre-cardinal veins may be regarded as anterior 

 vessels; doubtless also the ducts of Cuvier would serve as a 

 place of demarcation between anterior and posterior vessels. In 

 all of Stockard's figures and discussions the terms 'precardinal,' 

 'duct of Cuvier' and 'post-cardinal' are entirely wanting, so far 

 as I am aware. No term more definite than cardinal vein or 

 stem-vein is used. In the normal individual Stockard misin- 

 terpreted the ducts of Cuvier as vitelline veins. He figured 

 vitelline veins arising between the otocysts. If we admit that 

 the adult teleost has a duct of Cuvier, as is generally believed, 

 then the Vitelline vein' figured by Stockard are ducts of Cuvier 

 whose sources between the otocysts are the precardinal vein. 

 The term 'vitelline vein' is correctly used to distinguish particu- 

 lar yolk-sac vessels of a very definite morphology. Thus in the 

 normal individual, Stockard misinterpreted the ducts of Cuvier, 

 while in most of his experiments its development was prevented., 

 so that in neither case was he able to utilize the only satisfactory 

 landmark by which to determine the anterior vessels. No 

 doubt the embryos in many of Stockard's figures have erythro- 

 cytes in their precardinals. Figures from Wenckebach^ and es- 

 pecially those of McClure (36) demonstrate the fact that in 

 young stages the teleostean duct of Cuvier is well posterior to 



^ Hertwig's Handbuch, p. 1131. 



