502 



ESSENTIALS OF ZOOLOGY 



■ p^*¥»-* ' 



U^^ 





J 



..V 



^^^'' 



■Y 



I . 



1 











r\ 



At *. 



11 





II 



n 



■^''£il 





\ 



\' 



/ 



"^^ 



j 



■"Si 



'^ A 



^/h\ 





■■■vh 



'S< 





III ni . ^^^^ 





P^ 



c>rrc)< 



Fig 214.— The development of several vertebrate animals shown in three 

 parallel stages. Notice the close similarity of the first two stages tor all the 

 species shown. (From Romanes, Darioin and After Darivin. Open Court Publish- 

 ing Company.) 



