Statocyst control of the uropod movement in response to body rolling in crayfish

1. The steering movement of crayfish uropods in response to body rolling was analysed quantitatively. 2. The uropod on the upper side is spread out while the other one on the lower side is closed. Opening of one uropod was always accompanied by closing of the other. Positional changes of both uropods in response to body rolling were measured at 13 body positions. The response curve followed an approximate sine function in an intact animal 3. In a single-statocyst animal, increase of receptor activity in the intact statocyst caused opening of the ipsilateral uropod and closing of the contralateral one, while decrease of receptor activity had no effect on the uropod position. 4. A response curve obtained by algebraic summaion of two response curves in the animals with right and left statolith removed respectively was consistent with that of an intact animal with both statocysts. 5. It was concluded that each statocyst can produce bilateral uropod movement only in a limited range of roll angle since the receptor activity increases only when the statocyst hairs are deflected toward the inside of the sensory crescent. Bilateral uropod movement in an intact animal is produced by simple summation of inputs from the right and left statocysts. 6. Unilateral statolith removal caused an asymmetrical configuration of the uropods in the resting (0°) body position. The uropod on the operated side opened and that on the opposite side closed. This asymmetry was normalized day by day and the original symmetrical configuration was finally restored about 7 days after operation.