Marginal zone cells—the primitive streak-inducing component of the primary hypoblast in the chick

Abstract

(1) Removal of both the area opaca and the marginal zone of the area pellucida from ablastoderm stripped of its hypoblast (type-lV operation) prevents the regeneration of a normally functioning primary hypoblast. (2) Stage-XIIl E.G & K blastoderms (prior to the appearance of PS) after a type-lV operation do not form a primitive streak. (3) In older type-lV operated blastoderms in which the primitive streak has already begun to appear, the regeneration of a non-functional hypoblast did not support the normal maturation of the primitive streak, and in many cases the already existing rudimentary streak was absorbed. (4) Type-IV operated blastoderms from stage 3+ H & H and on developed normally. (5) It is concluded that the cellular contribution of the marginal zone to the primary hypoblast is instrumental in the latter's capacity to induce a PS.