1. Use is made of the fact that a freely moving blind eyecup is driven by movement perceived by the opposite seeing eye when the crab is in an optomotor drum.
2. Forced extension of the seeing eyecup causes movement of the other blinded eyecup in the opposite direction, because it is driven by the perceived relative motion.
3. Voluntary extension of the seeing eyecup causes no movement of the other blinded eyecup, although simultaneous oscillation of a striped drum round the crab is seen perfectly.
4. Preventing voluntary extension of the seeing eyecup with a mechanical stop causes no movement of the other, blinded, eyecup.
5. With both eyes blinded, or with the crab in the dark, voluntary or forced movement of one eyecup causes no movement of the other.
6. This behaviour is that expected of an animal which can retract and extend either eyecup in the light or in the dark without disturbing the other, but no simple model is compatible with all the experiments.
- Copyright 1968 The Company of Biologists Ltd.