2'^ 3 



fl 



^^ 



12 



n 



13 





22 



_ODOC);T^V>-'.''--:.. •.•':-.>,■.■•■.'•."'••.:"■•■ :. 



24 



DO OCT .-J 



'■•'v' «,«•">' 



25 





/.i«.<.TW.'-'f •,•■-■•• f/* 



17 



V^::::^^- 18 





20 





26 



c 



27 



p;,r ,no Phvsioloeical grad ents in the chick embryo (Hyman) 



tig. I02. rnysioiogic^i gi'i" A/f<.rq,.ll^rv n ate sta£ 



e 4-6. Head-process stage. ?■ 



romi.fs?ie;t6i7°FTv:rm!,r:.is.s'ho-;^g'h?rgh^^^^^^ 



fold stage. i4-i7- One-somite stage 



somite stage. 26-; . 



of fusion of neural folds. 



i-Q. Primitive streak 

 " ly ' 



18-20. Three-somite stage. 21-25. 



I the cnicK emuiyu i^ixyx^ciw;. . -J. ' PcrWrK-nral 

 ..age. 4^. Hjad-process stage. 7-.0. MeduUary (.a.e staje. ^. ,-.3. Early neu„^^ 



