Cell, developmental, and reproductive biology have been a central part of the MBL's programs since the 1890s. Important discoveries in these fields at the MBL reach back to 1899, when Jacques Loeb demonstrated artificial parthenogenesis in sea urchin eggs; to 1905, when Edwin Grant Conklin first identified egg cytoplasmic regions that are programmed to form certain tissues or organs; to 1916, when Frank Rattray Lillie identified circulating hormones that influence sexual differentiation (Lillie, 1944). In the MBL's first two decades, cytologists Edmund Beecher Wilson, Nettie Stevens and others made connections between the chromosomes and Mendelian heredity, while Wilson's colleague at both the MBL and Columbia University, Thomas Hunt Morgan, launched the field of experimental genetics (Pauly, 2000:158). Keith R. Porter, considered by many to be a founder of modern cell biology due to his pioneering work on the fine structure of cells, including the discovery of microtubules, carried out research at the MBL starting in 1937 and directed the laboratory from 1975-77 (Barlow et al., 1993: 95-115).