In organotypic expiants of early area vasculosa (22 h. of incubation) erythrocytelike cells differentiate, but without hemoglobin. Later vascular areas (48-72 h.) explanted with embryonic liver tissue differentiate erytrocytes that maintain their hemoglobin content for longer than controls (up to 12 days); the electrophoretic properties of this hemoglobin are those of embryonic hemoglobin until the 5th incubation day.