An experimental study of the life-cycle of the fresh-water spongeEphydatia fluvitilis in its natural surroundings.

The life cycle of three strains of the fresh-water spongeEphydatia fluviatilis, experimentally cultivated in a pond near Brussels has been studied.The complete experiment lasted four consecutive years.Seasonal histological fluctuations are described. They emphasise that this species overwinters in a highly disorganized stage and completely regenerates in the early spring.These observations constitute a first approach to the analysis of the induction mechanisms of sexual reproduction.They clearly indicate the necessity for the sponge to overwinter in the field, in order to be able to undergo a sexual reproduction. It is to be noted that the first oocytes appear every year at the beginning of the winter, a little while after the sponges have reached their typical disorganized stage.The stability of the strain throughout sexual reproduction is demonstrated.