4o8 



THE ORIGIN OF VERTEBRATES 



My 



JVc 



--Mel 

 -Mg 



A 



Fig. 159. — Diagrams to illustrate the Development of the Vertebrate 



Ccelom. (After van Wijhe.) 



A T ., central nervous system; A r c, notochord ; Ao., aorta; Mg., midgut. A, My., 

 myoccele ; Mes., mesoccele ; Met., metacoele ; Hyp., hypomere (pronephric). B 

 and C, My., myotome; Mes., mesonephros ; S.cl., segmental duct (pronephric); 

 Met., body-cavity. 



