Modeling the Living Embryo - 1997 Levin, M., & Nascone, N. (1997). Two molecular models of initial left-right asymmetry generation. Medical Hypotheses, 49(5), 429–435. https://doi.org/10.1016/s0306-9877(97)90092-x Nascone, N., & Mercola, M. (1997). Organizer Induction Determines Left–Right Asymmetry inXenopus. Developmental Biology, 189(1), 68–78. https://doi.org/10.1006/dbio.1997.8635