A detailed kinematic analysis of the mantle movements of swimming Lolliguncula brevis was made. Some data were also obtained on Loligo pealei. The qualitative and quantitative data provided are of use in discussing mechanisms of squid mantle function.
Several possible mechanisms of squid mantle re-expansion were proposed and investigated. The inhalant phase of jet propulsion is probably effected by contraction of the radial muscles, since thinning of the mantle wall accompanies re-expansion. The radial muscles may cause mantle re-expansion by contracting alternately with the circular muscles in response to nerve impulses, or by contracting alternately with the circular muscles in response to stretch cycles effected by mantle wall thickening in the power stroke, or by contracting continuously through both power and recovery strokes. Elasticity of the mantle tissue may contribute to mantle re-expansion. Neither pressure pumps nor a Bernoulli effect mechanism are effectors of mantle re-expansion.