The rôle of the body fluid in the movement of soft-bodied invertebrates - II. The extenstion of the siphons of Mya arenaria L. and Scrobicularia plana (da Costa)

Abstract

It is widely held that molluscan organs are protruded and extended by a forceful influx of blood, but observations and experiments on Mya and Scrobicularia show that this is certainly not true for the movements of the siphons of these two lamellibranchs. The siphons of Mya are extended by water being forced into them from the mantle cavity by the action of the adductor muscles of the shell. Changes in length and shape of the siphons of Scrobicularia are effected solely by an intrinsic mechanism consisting of longitudinal and radial muscle fibres together with beds of collagen. The muscles are antagonized through the blood contained within the siphonal walls which at all times retain a constant volume.