Attempts have been made to trace the life cycle of Bithynia leachi from shell measurements at regular intervals, as made before for Physa fontinalis (L.) (DE WIT). Animals have been captured by collecting plant material at random and sieving the shells. In this case the frequency curves of the shell heights often showed several modes, which made it rather difficult to draw detailed conclusions. The fact that part of B. leachi retire in the mud during the colder season was another intricate factor.