14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



Table 2 (with stages i to 10). —Supposed stages in the evolution of the central 

 and visceral nervous systems of the polychact 



o^ ■ 



O y_ * ^ open 



-• — • — •••»»» — < V 



I Oesophageal 



O^;;-;^^^ .' > closed 



Invagination 



dkr-f • simplified 



^ — • • — • — • — • • • — —- + 



*,^^^» •*• -l-fc-^ open 5 



~' • » • • • — e — 9 • — • • ~~ \ 



. ^. / 1st Pharyngeal 



^^^^:: ^ ^f *■ '[j fc--^ closed I (Upper Jaw) 



*ls I Invagination 



^^^::::^^ *^ "^'^^r^ . ^ _ simplifi ed^ j 



^^?^r^^-— W-' open 



^^^ _^ / 2nd Pharyngeal 



^^^^ ^^ **r^- - - - - c^g '^^4> \ (Lower Jaw) 



-^O^ I Invagination 



^^=:r^ * ^>--~-^ simplified I 



^*^--»--^- » *^ » — • — • — • — m O--10/ 



