Contributions to an analysis of the avian vitelline membrane's potential to promote outgrowth of the yolk sac-serosal membrane.

Explanted blastoderms of freshly laid chicken eggs expand their area during the first 44-45 hours of incubation by a factor of at least 11 if they are placed with the epiblast on the inner surface of explanted fresh chick vitelline membrane and provided with chick egg extract. This expansion is due essentially to the spreading of the yolk sac-serosal membrane. On turkey and duck membrane the expansion factor is about 6 and 3.8 respectively under otherwise identical conditions, but 1.9 only on a semisolid nutrient agar plate. Only the inner surface of the vitelline membrane has this growth-promoting potential, which markedly and progressively declines during incubation in ovo because of systemic factors rather than because of a direct influence by the outgrowing yolk sac-serosal membrane. Trypsinization of fresh chick vitelline membrane (1% trypsin 3 hours) reduces the growth-promoting potential to about 40% of its normal strength. The outgrowth of the extraembryonic tissues on vitelline membrane is better supported in the presence of a species' own egg extract than by extract from another species.