ON THE RESPIRATORY PLOW IN THE CUTTLEFISH SEPIA-OFFICINALIS

The respiratory flow of water over the gills of the cuttlefish Sepia o fficinalis at rest is produced by the alternate activity of the radial muscles of the mantle and the musculature of the collar flaps; mantle circular muscle fibres are not involved. Inspiration takes place as t he radial fibres contract, thinning the mantle and expanding the mantl e cavity. The rise in mantle cavity pressure (up to 0.15 kPa), expelli ng water via the siphon during expiration, is brought about by inward movement of the collar flaps and (probably) mainly by elastic recoil o f the mantle connective tissue network 'wound up' by radial fibre cont raction during inspiration. Sepia also shows a second respiratory patt ern, in which mantle cavity pressures during expiration are greater (u p to 0.25 kPa). Here, the mantle circular fibres are involved, as they are during the large pressure transients (up to 10 kPa) seen during e scape jetting. Active contraction of the muscles of the collar flaps i s seen in all three patterns of expulsion of water from the mantle cav ity, electrical activity increasing with increasing mantle cavity pres sures. Respiratory expiration in the resting squid Loligo vulgaris is probably driven as in Sepia, whereas in the resting octopus Eledone ci rrhosa, the mantle circular musculature is active during expiration. T he significance of these observations is discussed.