INDUCTION OF (PRE)GASTRULATION AND OR (PRE)NEURULATION BY SUBGERMINALOOPLASM AND RAUBERS SICKLE IN CULTURED ANTI-SICKLE REGIONS OF AVIAN UNINCUBATED BLASTODERMS/

Rauber's sickle fragments from unincubated quail blastoderms, associat ed or not with chicken central subgerminal ooplasm, were placed on the deep side of the upper layer (UL) of the isolated anti-sickle region of unicubated chicken blastoderms and cultured in vitro. When only a R auber's sickle fragment was placed, we observed always a pronounced th ickening of the UL (pregastrulation) in the immediate neighbourhood. S ome times a primitive steak (PS) developed. When the Rauber's sickle f ragment was ''sandwiched'' between the UL and a central subgerminal oo plasmic mass [containing the nucleus of Pander (1817)], always a (pre) neural plate accompanied by endophyll developed, not or well associate d with a primitive streak. In the latter case a complete miniature emb ryo developed. De novo formation of endophyll was observed. As it cont ained quail nuclei it was derived from Rauber's sickle cells which col onized the subgerminal ooplasm. Our experiments indicate that the unco mmitted upper layer (UL) of the anti-sickle of unicubated blastoderms constitutes an excellent reactor tissue for inductions. The thickening induced in the UL of the anti-sickle region by Rauber's sickle initia tes (pre)gastrulation and the thickening induced by endophyll initiate s (pre)neurulation. IN the beginning, pregastrulation and preneurulati on seem to be independent phenomena. It is only later, when both becom e correctly linked at the right place and time, that a normal embryo w ill develop.