NEURONAL CO-ORDINATION OF RHYTHMIC MAXILLIPED BEATING IN BRACHYURAN AND ANOMURAN CRUSTACEA

1. 1. The neuronal mechanism which co-ordinates the rhythmic beating of the flagella of the three pairs of maxillipeds has been investigated in nine species of Decapod Crustacea, by recording the electrical activity in the abductor muscles of the flagella in unrestrained animals. 2. 2. The arrival of two or three impulses in two motoneurones leads to a single twitch contraction of the abductor muscle and a single beat of a flagellum. The return stroke to the adducted position is passive and is caused by elastic recoil. 3. 3. The three flagella on one side beat in a strict temporal sequence in which the third flagellum leads, followed after a constant delay by the second and then the firts. For a given animal there is a fundamental frequency of beating, which is the same for the maxilipeds of both sides, regardless of whether both sides beat together (Anomura) or alternate (Brachyura). When both sides beat together, there is a fixed and constant delay which separates the beat of a flagellum on one side from the other. 4. 4. There is close co-ordination between the unilateral beating of the maxillipeds, the direction of walking and movements of the antennules. 5. 5. It is possible to account for these details of co-ordination with a unit level neural model in which a single pacemaker controls a short open chain of interneurones with fixed but different synaptic delays to the motoneurons of each flagellum. © 1969.