Observations on Pigmentary Co-Ordination in Elasmobranchs

Abstract

Section of the spinal nerves to the pectoral fins in Raia brachyura, R. maculata and Scyllium canicula had no effect on the state of the chromatophores in the black adapted fish, nor did it prevent the development of uniform pallor on a white ground. Electrical stimulation of (a) spinal nerves to the pectoral fins, (b) the haemal canal, (c) the skin, in Raia brachyura, Rhina squatina and Scyllium catulus did not result in any chromatophore changes. Excised skin of Raia brachyura, R. mandata, Rhina squatina and Scyllium canicula placed in adrenaline chloride solution showed little or no change in melanophore index during one hour and could not be differentiated from control pieces placed in elasmobranch Ringer. The injection of adrenaline chloride caused a slight paling in Raia brachyura and Rhina squatina. This may be a secondary effect due to the vaso-constrictor action of this hormone. White adapted specimens of Raia brachyura, which were placed on a black ground after ligature of the dorsal aorta, became dark anterior to the point of ligature within 3 hours. The posterior region was still completely pale at this time and did not become fully dark for 24 hours.