Further Studies of Crayfish Escape Behaviour I. the Role of the Appendages and the Stereotyped Nature of Non-giant Escape Swimming

1. High-speed cinematography of the escape behaviour of freelymoving crayfish showed that the thoracic and abdominal appendages exhibit stereotyped movements in giant axon-mediated tail flips and in non-giant flips. Three distinct classes of non-giant tail flips were recognized in this study: linear, pitching and twisting flips. 2. In medial giant flips and linear non-giant flips the chelipeds and pereiopods were promoted and extended in a manner which minimized the hydrodynamic resistance of the animal. The exopodites of the uropods were promoted. In lateral giant flips and pitching non-giant flips the thoracic appendages moved only passively. The uropod protopodites were promoted but the exopodites remained remoted. 3. When giant axon-mediated tailflips were elicited with natural stimuli they were followed by sequences of non-giant flips which appeared quite stereotyped.