The statocyst of the squid Loligo

Abstract

The cavity of the statocyst is shaped and divided to provide angular accelerometers by action of the inertial mass of endolymph upon the cupulae. Some of the anticristae that make the divisions become joined in adult Loligo, producing rather well‐defined canals. These direct the flow across the vertical crista, monitoring movements in the yawing plane. Movement of endolymph across the other sections of the crista is not restrained into canals but is directed by the anticristae and by the shapes of the sacs above and below them. The arrangement of the posterior transverse crista suggests that it may monitor linear accelerations forwards and backwards.The hooks (hamuli) at the ends of each part of the crista serve to restrict the effective flow across the cupulae. The hamuli are absent at hatching and they grow continually, maintaining a small cupula gap. These conditions are compared with those in the semicircular canals of vertebrates.The afferent nerve fibres of the crista have a small diameter at their origin, increasing rapidly to 40 µm. They run directly to the brain. The small, presumably efferent, fibres run complex courses along the crista before forming networks around its cells.The walls of the statocyst are largely covered by a plexus of nerve fibres connected with the nerves of the crista. The plexus contains few nerve cells and the origin of its fibres is uncertain.Cells beneath the epithelium send ciliated projections into the cavity. They carry an elaborate basal network of fibres in the outer statocyst wall. Their significance is not known.