ALBERT

Notes: Summary 1. Certain groups of melanophores on the head ofPhoxinus can be denervated by severing the ophthalmic branch of the Trigeminal nerve. Other definite groups of melanophores on selected areas on the trunk ofPhoxinus can be denervated by severing one or more spinal nerves or cutting loose a bit of the skin from its underlying cutaneous nerves. 2. Those denervated melanophores on the head and those on the ventral portions of the trunk contract either partially or completely when the fish is set upon a white background. 3. Those denervated melanophores on dorsal portions of the trunk contract either partially or remain expanded when the fish is set upon a white background. 4. All denervated melanophores remain maximally expanded when the fish is left upon a black background. 5. Those denervated melanophores which failed to contract when the fish was set upon a white background will do so if one threatens the fish or attempts to capture it. 6. With the circulation intact these denervated · melanophores all contract following electrical stimulation of the medulla or when the fish is set between two stimulating electrodes, as do the innervated melanophores on the rest of the body. Following the cessation of such stimulation all innervated melanophores rapidly expand, while the denervated melanophores remain well contracted. 7. With the circulation stopped by removal of the heart the denervated melanophores no longer contract during electrical stimulation, though the innervated melanophores continue to do so. 8. If the melanophores over a large body area are denervated by severing the sympathetic cord and if the area affected by this operation includes regions previously denervated by other means, the fish being kept meanwhile upon a white background, the melanophores of these smaller previously denervated regions fail to show the immediate and pronounced expansion characteristic of these cells in other parts of the freshly denervated area. 9. In fishes kept upon a white background the trunk melanophores denervated by severing the sympathetic cord usually contract completely if they are located ventrally, while those cells lying dorsally contract as a rule only partially if at all. 10. When the hearts are removed from fishes previously adapted for a week or more to a white background the animals remain pale for at least a half hour after the operation. Eventually however they darken. When the hearts are removed from fishes previously adapted to a black background for a week or more but set upon a white background immediately after the operation these animals show a momentary paling which does not include the denervated areas. This slight-paling is immediately followed by a pronounced darkening of the entire body. 11. Fishes with denervated head areas kept upon a background of alternating white and black spots show a partial contraction of their innervated melanophores as well as a complete expansion of their denervated melanophores. 12. The following general conclusions were drawn from these experiments: a) Upon a white backgroundPhoxinus elaborated some hormone or hormones not definitely identified but suspected to be adrenalin capable of contracting denervated melanophores either partially or completely. This hormone also supplements the action of the nervous system in bringing the innervated melanophores to a complete contraction on a white background. b) No evidence was found of any hormone capable of expanding the melanophores. The question is left open whether such a hormone exists. c). The melanqphores ofPhoxinus vary in the degree to which they are influenced by this contracting hormone, the denervated cells on the head and ventral portions of the trunk being more readily brought to a complete contraction than those on the dorsal portions of the trunk.