COMPAEATIYE ANATOMY. 



Fro. 7, A AND B. DIAGRAMMATIC TRANSVERSE SECTIONS THROUGH A DEVELOPING 

 VERTEBRATE EMBRYO. 



D, alimentary canal ; Ent, hypoblast, showing in Fig. A the thickening which will 

 form the notochord ; Ch l (Fig. B), the note-chord now constricted off from the 

 hypoblast ; UW, mesoblastic somite ; UGf, primary urinary duct (segmental 

 duct) ; A, aorta ; SpP, splanchnic and SoP, somatic mesoblast ; Co, God, ccelome ; 

 Hj remains of the upper part of the ccelome in the interior of the mesoblastic 

 somites ; EJct, epiblast ; Med, medullary cord : in Fig. A it is shown still con- 

 nected with the epiblast, from which it has become constricted off in Fig. B. 



A large cleft appearing in the mesoblastic tissue divides it into 

 a parietal layer (Fig. 7, A and B, SoP), lying along the inner 



