Observations on the locomotion of two British terrestrial planarians (Platyhelminthes, Tricladida)

The locomotion of Microplana terrestris and of M. britannicus is described. Forward locomotion is normally by means of cilia which are confined to the ventral surface of the animals. M. terrestris may however involve stationary peristaltic waves in locomotion. In this case neither muscular nor ciliary forces can alone account for the locomotion and it is necessary that the two mechanisms are combined. Such stationary waves should be distinguished from retrograde and direct locomotory waves. Reversal in both species is by retrograde muscular waves.