408 THE ORIGIN OF VERTEBRATES 
Fig. 159.--D1aGRAMS TO ILLUSTRATE THE DEVELOPMENT OF THE VERTEBRATE 
Catom. (After van W1JHE.) 
N., central nervous system; Ne., notochord; Ao., aorta; Mg., midgut. A, My., 
myoceele; Mes., mesocele; Met., metaccele; Hyp., hypomere (pronephric). B 
and C, My., myotome; Mes., mesonephros; S.d., segmental duct (pronephric) ; 
Met., body-cavity. 
