Figs. 21 to 23 Ventral view of a model of the mesoderm (white), sijlanchno- 

 ])leiirie mesenehyiiic (green), vasofaetivo eells (yellow) and endothelium (red) 

 i)f -All cniliryo ul' two Homites. ('(iluiiiliia f 'iillcction Xo. 539, X 300. Hediiced J. 



1 Anlage.s of ventral aorta and heart .'i From this point craniad the meso- 



2 Anlages of dorsal aorta derm is continuous across the 



3 First intersomitic cleft median line 



4 .Second intersomitic cleft From this jioint caudad the meso- 



derm is colli inuous ai'ross the me- 

 dian line 



76 



