 len develop differenti embryon chick len epitheli cell vitro vivo behavior len epitheli cell six-dai chick embryo studi three experiment situat explant fluid cultur media explant reimplant lensectom embryon ey explant reimplant embryon coelom caviti specimen examin histolog total volum len materi specimen determin planimetri serial section interpret 1 small amount protein supplement cultur medium embryon len epitheli cell capabl limit amount independ cytodifferenti protein supplement fail undergo fiber format 2 return ey environ cultur epitheli explant respond resumpt growth cellular differenti morphogenet chang form len embryon coelom support respons 3 initi format len fiber suffici complet autonom matur 4 intern architectur develop len determin shape 