The Relation of the form of a Sponge to its Currents

Abstract

ABSTRACT All zoologists know that from the large holes, which we call oscula, on a sponge, an outgoing current may be detected in life. During several months in Naples I investigated this current, using litmus and carmine solutions, and carmine and indigo in suspension. I worked with two calcareous species of sponges, having oscula at the end of tubular prolongations, which reach the size and shape of a child’s thumb in the case of Leucaltis, and of a child’s finger in the case of Leucandra aspera (Text-fig. 1). The solutions were either placed on the surface of the sponge, to be sucked in by its currents (Text-fig. 2), or dropped by a pipette through an incision into the cloaca—the cavity of the tubular prolongation. In the latter case the time taken for the colour to be thrown out at the osculum, though liable to many corrections, afforded on the whole the most trustworthy determinations of oscular velocity: the cloaca being wider than the osculum, the observed cloacal velocity would be multiplied by 4, 5, or 6, as the case might be, to obtain the oscular velocity. A pretty method was arrived at accidentally (Text-fig. 3), when I found the coloured jet marked by dark beads or nodes, caused by my pulse shaking the pipette; the length between any two nodes, divided by three-quarters of a second, gives the core-velocity at that part of the jet.