ABSTRACT
Pl. alpina is normally active in the evening and quiescent during the day.
Pl. alpina is shown to become positively rheotactic when developing sexually, but becomes negatively rheotactic on completing the sexual cycle.
Starvation leads to de-dififerentiation and the loss of positive rheotaxy.
Feeding produces a temporary positive rheotaxy and a temporary negative geotaxy.
Continued feeding leads, if temperature conditions are suitable, to the re-development of those characters which produce positive rheotaxy in sexual individuals.
The development and consequently the behaviour of PL alpina is controlled by temperature and the food supply.
Considerable migrations up and down the stream are brought about by changes in the animal’s behaviour.
It has been found possible to dispense with the periodic siphon B, since a long elastic attachment causes of d sufficient to maintain the periodicity necessary for the working of the apparatus.
