492 



HEMICHORDA 



The body cavity .-The body cavity consists of five 



Fig. 270.— Dissection of Balanoglossus. 



r,n r- ^^^Kr,cfic ravitv " Nck., notochord ; 



N., nerve'; PH., outer Pharynge^^ ^^ ; G.S., gill slits. 

 The main blood vessels are stippled (B.V.). 



distinct parts, all of which are lined by mesoder,^ and 

 arise as pouches from the archenteron. (a) There is tirst 



