AVIAN GASTRULATION AND NEURULATION ARE NOT IMPAIRED BY THE REMOVAL OFTHE MARGINAL ZONE AT THE UNINCUBATED BLASTODERM STAGE

In the present study, we removed the whole area marginalis, Rauber's s ickle and the peripheral part of the area centralis from unincubated c hicken blastoderms (st IV, Vakaet, 1962a). By placing a fragment of a quail Rauber's sickle (functioning as early gastrulation organizer: Ca llebaut and Van Nueten, 1994) at different places and oriented in diff erent directions on the remaining central part of the area centralis, Mie observed, after in vitro culture, a normal embryonic development. This indicates that the area marginalis itself is not indispensable fo r gastrulation and neurulation. Our study also indicates that none of the three elementary tissues (Rauber's sickle, endophyll and upper lay er) of the avian unincubated blastoderm present art irreversible funct ional polarity.