Autotomy is the specific action by which a limb of an animal is rejected by a reflex action. In Carcinus maenas (L.) any single pereiopod may be rejected following gross inflicted damage. Tension measurements of the muscles involved in this action indicate that previous accounts of the mechanism of autotomy cannot be entirely correct. There are two basi-ischiopodite levators of which the anterior one is by far the larger. This muscle is responsible for both walking movements and autotomizing the limb but both actions are reliably separated as autotomy requires the specific intervention of the posterior levator. The tendon of the posterior levator rests against that of the anterior levator. Rotation of the posterior levator tendon separates a hitherto unsuspected preformed breakage plane in the tendon of the anterior levator which radically alters the action of this muscle.
The mechanism proposed here by which autotomy in Carcinus maenas is effected, shows that the shedding of a limb is a specific act and not merely an extension of a normal limb movement as has been supposed.