A bifunctional single motor axon system of a crustacean muscle

It is shown that the opener muscle of the hermit crab, Eupagurus bernhardus L., receives a single motor axon. Stimulation of this axon results, when appropriate stimuli are used, in two types of contractions comparable with the fast and slow contractions of doubly motor-innervated crustacean muscles. The theoretical implications of this finding are discussed and a hypothesis offered to explain the mechanism which makes the two contraction types possible. The physiological and anatomical features of the innervation of the four most distal muscles in the legs of Eupagurus are described