The Development of the Heart in Shad. 217 



ventral surface of the splanchnic peritoneum is, however, lined 

 by vascular endothelium which eventually forms the hepatic vein^ 



The hepatic vein then in Type 1, replaces the vitelline network 

 of Type 2, and it might itself be considered a vitelline vessel, but 

 for the fact that when it is fully formed the yolk is reduced to a 

 very small size. The light in which the hepatic vein is regarded, 

 however, does not affect the essential validity of the types: Embryos 

 of Type 2 differ from those of Type 1 in that they possess, at some 

 period prior to the disappearance of the yolk, vitelline vessels lateral 

 to the margin of the coelon. 



In all cases in which the site of origin of the blood corpuscles 

 has been investigated in embryos of Type 2,® it has been found to 

 occur in the cardinal veins, which may be separate or partially 

 conjoined (Stammvene). In embryos of Type l*^ the cardinal veins 

 have invariably been found, when they first appear, to contain no 

 corpuscles. 



At the present time, although the information at our command 

 is rather suggestive, it appears neither safe to assume that the 

 blood anlage is alivays developed within the cardinal veins in embryos 

 of Type 2, nor that this never happens in embryos of Type 1. It 

 would seem that more information is needed on the entire subject 

 of blood-formation in teleosts, before a generalization of this kind 

 can be made with safety. I refer particularly to the fact that 

 Marcus ('05) has recorded for Gobius capito (Type 2) that 

 corpuscles arise in the tail as well as in the cardinal vein region; 



^It is neither assumed nor implied tliat the formation of tlie hepatic vein in 

 other embryos belonging to Type 1 is similar in mechanism to that later to be 

 described for shad; the serial sections of other Type 1 eggs, mostly pelagic, 

 in the possession of the writer do not cover all the stages necessary for the 

 determination of this point. 



^Zeigler, '82 and '87, Salmo salar ; Wenckelbach, '85, Perca fliiviatilis, '86 

 Belone and Esox ; Felix, '97, salmon and ti-out ; Swaen and Brachet, '00, trout, 

 '02, Leuciscus cephalus, and Exocoetus volitantes ; Sobotta, '02, Trutta fario, 

 T. iridea and Salmo salvelinus ; Marcus, '05, Gobius capito. 



'Wilson, '91, Serranus atrarius (Centropristis striatus, L) ; Sween and 

 Brachet, '02, Clupea sprattus, Rhombus (?), Solea vulgaris, Pleuronectes 

 microcephalus, Trachinus vipera, Caranx trachurus, and Calliouymis lyra ; 

 Derjugiu, '02, Lophius piscatorius. 



