On the origin of primordial germ cells in the chick embryo.

An attempt was made to re-examine the location of the primordial germ cells (PGCs) in very young chick embryos. Freshly laid blastoderms, prior to hypoblast formation, of a known anterio-posterior axis, were transversely bisected and each half was separately grown in vitro. Both anterior and posterior halves were shown to be fertile and each was shown to contain roughly the same amount of PGCs as a normal control embryo. It has been concluded that in the chick as well as in the duck there is no concentration of cells containing germinal plasm in the posterior part of the blastoderm. Two other possibilities should be investigated: 1. A concentric arrangement of cells containing germinal plasm. 2. The absence of a germinal plasm and a relatively late appearance of PGCs as a result of induction.