74 CHARLES R. STOCKARD 



supposed. The relation of the blood anlage to the cardinal 

 vein and the position of the blood forming cells dorsal of the gut 

 are unique in the Teleosts. The late formation of the yolk vessels 

 and their type of origin from wandering mesenchymal cells is 

 also of special interest. 



It would seem as though the peripheral mesoblast which in 

 other vertebrate types grows and develops outside the embryo, 

 had in the Teleosts been peculiarly concentrated and drawn into 

 the embryo during its phylogenetic history. Yet in this intra- 

 embryonic position the peripheral mesoblast gives rise to the 

 same cells which it would ordinarily produce on the yolk-sac. 

 The different Teleosts probably show this drawing in of the 

 peripheral mesoderm to various degrees so that in some cases 

 only part of the mesoderm is incorporated in the interme- 

 diate cell mass, while the remaining part may still be outspread 

 upon the yolk and there differentiates extra-embryonically. 

 The intermediate cell mass is connected caudally with the end 

 bud, just as the peripheral mesoblast of the Selachians is with 

 the blastopore lip. In its genesis the intermediate cell mass is 

 split off from the lateral plate and localized along its median 

 border. 



Marcus ('05) in his study on Gobius capito advanced the 

 opinion that the intermediate cell mass in this embryo is compar- 

 able to the peripheral blood forming mesoderm of other mero- 

 blastic eggs. In an embryo of eleven somites, the intermediate 

 cell mass passes without a break caudad to the end bud and there 

 connects with both the ectoderm and entoderm, just as the peri- 

 pheral mesoderm would meet the other two germ layers at the 

 blastopore lip. He attempted to show by diagrams the rela- 

 tionship between the intermediate cell mass in Teleosts and the 

 blood forming mesoderm of Selachians. 



As the homologue of the peripheral mesoderm the intermediate 

 cell mass has the power to form vessels and blood cells. Most 

 authors admit this power and only Sobotta ('02) denies the ves- 

 sel forming property, while others claim that only the cardinal 

 veins arise from the intermediate cell mass, still others, as Swaen 



