Figure 2.

Series of five avoidance reactions observed in S. roeseli. This is Vance Tartar's illustration of the five reactions of S. roeseli stimulated by carmine in the order described by Jennings [11]. As long as the stimulus is still present in the surrounding environment, these five reactions are: (a) no response—at rest. (b) Bending away from the source. (c) Transient stop of cilia beating, reversal of spiralling direction. (d) Strong full contraction. (e) Detachment and swim away. (Online version in colour.)