Responses ofBranchiomma Vesiculosum(Montagu) to photic stimulation

Abstract

In Branchiomma vesiculosum decrease in light intensity causes the animal to contract and withdraw into its tube. A decrease, never an increase, in illumination is the effective stimulus. When repeatedly stimulated the animals quickly become adapted to intensity changes and no longer respond.The minimal effective intensity change has been determined for a range of intensities. ΔI/I is found to increase in low light intensities, and to be fairly constant in intensities over 50 lux. The animals are least sensitive to red light; sensitivity increases in shorter wave-lengths.