Compatibility and nutritional dependence of mouse egg cylinder fragments associated with amphibian embryonic tissues

rum, using two techniques. One lot of fragments was implanted into the blastocoel ; the second lot was cultured in vitro in association with undetermined epiblast excised from the ventral half of the blastocoel roof. All samples were cultured up to 3 days in Barth’s solution, optimized for the amphibian embryo and not permitting isolated mouse egg cylinder fragments to survive. Small grafts, completely surrounded by Bufo cells, had an apparently normal aspect and frequent mitotic figures. Large grafts, attached to the host embryo, were in close contact with the endoblast and mesoblast cells, but the ectoblast layer showed no ten-