THE ANCESTRY OF THE VERTEBRATES 



stc. 



p.e. p Of g- St c- 



655 



Thp^ ?i'i„/t?;T°Vi?''^™u '"ustratmg the principal stages in the evolution of segmented animals. 

 rln=r^„ ^f fvfi li substitution of one organ for another. The most striking illustration is the 

 ,>, ?l»^.» ■ ?! "IT^^"- f-n'i stomodeum and the formation of a new opening into the mesenteron 

 k thl ^t^^Zi- *''«, dorsal organ ; the substitution of lungs for gills. The most striking innovation 

 ^PtTJilJl^^- % * D "If "^ ^^P^''^^"? gill sacs and enteric diverticula; the rise and decline of 

 metamerism. (From Patten's "Evolution of Vertebrates and Their Kin.") 



