VERTEBRATE AND INVERTEBRATE 



Fig. i (upper block). — Schematic view of a typical chordate animal in the 

 region of the gill-slits. 



Part of the wall of the body is represented as removed in order to reveal 



the interior. 



Fig. 2 (lower block). — Transverse section through a typical chordate 

 animal (an embryo dogfish). 



c, splanchnocoel ; d, cutis-layer or dermatome ; da, dorsal aorta ; dn, 

 dorsal nerve-root ; g, gut ; gs, gill-slit ; m, myotome ; mc, myocoel ; ms, 

 mesentery ; n, notochord ; nc, nerve-cord ; nl, nephroccel ; nr, neural 

 crest ; nt, nephrotome ; o, opening of gill-slit ; sc, sclerotome ; si, sub- 

 intestinal blood-vessel ; so, somatopleur or body-wall ; sp, splanchnopleur 

 or gut-wall ; v, blood-vessel running in the gill-arch between the gill-slits ; 

 vn, ventral nerve-root. 



