Motor Performances of Some Cephalopods

ABSTRACT It has long been recognized that contraction of the mantle muscles of a pelagic cephalopod produces high hydrostatic pressure in the mantle cavity, a jet of water from the funnel and movement of the animal in the opposite direction (Fig. 1). As a result of their investigation of the responses of squid muscle to repetitive stimulation of giant nerve fibres, Prosser & Young (1937) considered that the expulsion of each jet of water, occurring in locomotion, is a single unitary act which is performed in an all-or-nothing manner. Absence of any increased response in fresh muscle preparations at higher frequencies showed that a single nerve impulse carried by a giant axon is capable of activating every muscle fibre that it reaches. In parallel with the decapod fast system there is a slow system made up of many small-diameter nerve fibres, which when stimulated provoke smaller graded muscular contractions in a mantle preparation (Young, 1938). This author assumed that these graded contractions produced the mantle movements involved in respiration. The graded contractions were further studied by Wilson (1960) who demonstrated that Octopus (O. bimaculatus and 0. bimaculoides) also have a fast and a slow system. The fast system of Octopus, unlike that of the decapods, shows marked facilitation of the mechanical response and a single: twitch takes 160 m.sec. to reach maximum tension. Summation of Octopus fast and slow systems and of the squid slow response take place in a two-phase manner, a rapid increase in tension being followed by a slower rise.