VARIABLE TENSILITY OF THE LIGAMENTS IN THE STALK OF A SEA-LILY

The stalk of isocrinid sea-lilies consists largely of skeletal plates linked by collagenous ligaments. Although lacking contractile tissue, it can bend in response to external stimuli. The stalk of Cenocrinus a sterius was tested mechanically to determine whether the mechanical pr operties of its ligaments are under physiological control. In bending tests, ligaments at the mobile symplexal junctions showed a limited '' slackening'' response to high K+ concentrations which was blocked reve rsibly by the anaesthetic propylene phenoxetol. In bending tests and u niaxial loading tests, ligaments at the normally rigid synostosal junc tions ruptured in response to high K+, confirming that these junctions are specialized for autotomy. It is concluded that the ligaments are mutable collagenous structures whose presence explains the mechanical versatility of the isocrinid stalk.