Sexual Differentiation in Hydra in Relation to Population Density

RECENT reports by Loomis and by Loomis and Lenhoff1 of controlled induction of sexual differentiation in Hydra littoralis have stimulated considerable interest in this process. One of the observations reported is that hydras differentiate sexually in crowded cultures but remain asexual when uncrowded unless the cultures stagnate. This observation is of particular interest because mass cultures of the clone of Hydra littoralis used by Daniel and Park and by Park2 remained continuously asexual for as long as three years. Although culture conditions were considerably different from those described by Loomis, population density and degree of stagnation were apparently comparable.