The Influence of Water and Light Upon the Pigmentary System in the Common Frog Rana Temporaria

Abstract

A significant influence of water in relation to colour change in Rana temporaria has been established. Its action on the melanophores in relation to background shows it exerts an independent influence. Thus (a) with a black illuminated environment, water accentuates the background response, (b) with a white illuminated environment there is antagonism, (c) in darkness the presence of water induces extreme expansion, and drying induces contraction, but only after prolonged periods. Immersion on a white illuminated background causes immediate expansion, and prolonged drying even upon a black background induces contraction. During the breeding cycle, the males fail to darken when immersed upon a white illuminated background. This particular seasonal effect is not shown by the females. It was further shown that the water response is independent of the primary response. The greater the degree of immersion, the greater the degree of expansion maintained upon a white illuminated background, so that the area of contact is significant, and it is highly probable that skin receptors are concerned. The lower oxygen tension of water as compared with that of the atmosphere was not a significant factor in the expansion of the melanophores due to immersion.