The Rate of Movement of Planaria alpina

Abstract

1. The rate of movement and the length of the periods of activity of Pl. alpina are increased by raising the temperature, except at very low temperatures. 2. The normal rate of movement appears to be controlled by a balance between two nervous processes, one being excitatory, the other being inhibitory. 3. The inhibitory process is broken down at the higher temperatures before the excitatory or muscular mechanisms are damaged. 4. Starvation may lead to a slight increase in the rate of movement. 5. External stimuli affect the rate of movement. 6. The chemo-receptors are situated on the extreme anterior border of the head. 7. The effect of temperature on the normal rate of movement gives no information regarding the chemical reactions responsible for muscular contraction. 8. Pl. alpina cannot tolerate indefinitely temperatures higher than 12° C. 9. Under natural conditions Pl. alpina is never found at temperatures above 15° C