DEVELOPMENT OF THE CIRCULATORY SYSTEM 



841 



edges, between the epiblast and the hypoblast, and these, which are 

 called parablastic cells, are developed into bloodvessels and blood-cor- 

 puscles. The connective tissue also is supposed to be developed from 

 parablastic cells. According to this view which, however, is not gen- 

 erally adopted the parablastic cells are to be distinguished from the 



Fig. 244. Area vasculosa of a rabbit of eleven days (van Beneden and Julin). 

 The capillaries are not shown in this figure. 



cells of the mesoblast, which latter are called archiblastic cells. Ac- 

 cording to Rindfleisch, the so-called parablastic cells are derived from 

 the area opaca. 



TJie First, or Vitelline Circulation. In the development of ovipa- 

 rous animals, the first, or vitelline circulation is very important ; for by 

 these vessels the contents of the nutritive yolk are taken up and carried 

 to the embryo, constituting the only source of material for its nutri- 



