The onset of cutaneous pigmentation by melanophores in three different types of wound of the operculum carried on simultaneously in three different tanks of running water at 76° F. was uniformly between the third and fourth day after trauma. The final disappearance of pigment of degenerated melanophores of the wound area varied between 6 and 19 days after injury. In some fishes the accumulation of melanophores noted at the wound was relatively slight; in others the black pigmentation caused by large numbers of melanophores was intense and remained over a longer period. Fishes operated on during the cold winter months and kept in tanks of cold running water (43° F.) did not show at wounded areas such a rapid development of melanophores as described in the preceding experiment. Further, pigmentation of wounds under winter temperature extended over longer periods. Thus, in nine fishes with right operculum crushed for 15 seconds with an artery clamp placed at the middle of the operculum, followed by excision of opercular tissue distal to the operculum, the following results were obtained: An eruption at the injured operculum in all nine fishes occurred between 13 to 16 days after injury; pigmentation had cleared up by degeneration of melanophores in only three fishes two months after injury, with temperature of water at 53° F. It took approximately one more month (temperature 53°-56° F.) for four more fishes to clear; the remaining two fishes cleared at the end of still another month or four months from the date of injury, when the temperature of the water had gradually risen to 61° F. The longest period of pigmentation in a wound of this series represented approximately 110 days from the date of the first appearance of melanophores. It became of interest to learn whether or not in fishes kept in very cold water, an appearance of melanophores after trauma could be temporarily inhibited, to appear for the first time when such fishes were changed back slowly to more favorable warmer temperatures. A number of experiments were done along these lines. Experiment 4. A goldfish, seven cm. in length, was placed in a tank of still cold water supplied by a current of air, the water varying in temperature between 42° F. and 45° F. The tank was set up in a refrigerator arranged with a double window, admitting ample daylight. It was found advisable to accustom the experimental fishes gradually to cold. By using several submerged electric lights at the beginning of the experiment and turning these off as desired, the temperature of the water could be lowered slowly without endangering the life of the fish. Oct. 14, 1930. A small incision was made with a cataract knife in the caudal fin of this goldfish dividing transversely a single ray near the upper margin of the fin. Examination of melanophores at four day intervals negative for an entire month. Temperature 42° to 46° F. Nov. 14. Temperature in tank raised slowly so as to reach 66° F. on Nov. 16th. Nov. 16. Numerous melanophores appeared for the first time at fracture and along injured ray distal to this. No other black pigmentation noted. Nov. 25. Slight pigmentation by melanophores of tip of tail and also along the margin of dorsal fin. Large accumulation of melanophores at fracture. Nov. 27. Active degeneration of melanophores at fracture and other pigmented regions. Nov. 29. Fish under dissecting microscope shows no pigment masses either at site of experimentally fractured ray or at the secondary points of black pigmentation of tail or dorsal fin. All melanophores have disappeared by a process of degeneration. Fishes kept in a dark chamber, excluding all light, developed melanophores in wounds as promptly as did controls kept in daylight. Experiment 5. Two goldfishes, seven cm. in length, with crushed right operculum and caudal fin, kept in a dark chamber in a tank of still water at 64° F., supplied by air current, were taken out of this chamber to be examined for the first time after injury on the fifth day. Many melanophores were present in crushed regions. At the same time, two control fishes, injured on the same day in a similar way, kept in a tank of equal size at the same temperature but exposed to laboratory daylight, exhibited, also for the first time, a large number of melanophores at the two crushed points. Twenty-three days after injury, one fish contained in the dark chamber and both controls were clear of pigment; the second fish in the dark chamber showed no melanophores in the injured operculum, although a few small masses of degenerated pigment masses still remained in the caudal fin. The production of a second injury in a healed wound frequently, but not always, caused another eruption of melanophores. Refracturing a single ray at the same point, especially where the previous healing had left a wide whitish translucent area, did not produce a second crop of melanophores. The very simple injury of making a longitudinal slit in the caudal fin did not call forth melanophores either at the time of the first injury or with repeated incisions at the same point. The irregular topographic distribution of melanophores following trauma was seen particularly well in experiments where the scales on both sides of the body were totally removed. Experiment 6. Nov. 1930. Three goldfishes, A, B, C, measuring 8, 7, 5 cm. in length respectively, kept in a heated tank of still water 76° F., supplied by air current, were operated on under chloretone anæsthesia (1-2000). All scales of the body were removed with forceps in all three fishes. Dec. Four days after operation, melanophores appeared in irregular groups at various points on both sides of the body. The two larger fishes, A and B, showed in the course of the next few days a large number of melanophores in irregular scattered patches. The patches of pigmentation by melanophores in fish B are shown in Fig. 6. The smallest fish, C, showed only a few melanophores in small, widelyscattered areas. By the end of the twelfth day degeneration of melaophores evoked by removal of scales had occurred in all three fishes with a disappearance of broken-down pigment material. At this time (12 days after removal of scales) each fish showed definitely a set of new young scales. Fish B successfully withstood a second complete removal of scales, under chloretone anæsthesia, but this time only a very few rapidly degenerating melanophores developed on the denuded surface of the body, as if the supply of pigment-forming cells for these particular surface areas were partially exhausted. When, however, on the fourth day after the second operation for removal of scales the caudal fin of this fish was crushed by clamp for 15 seconds, numerous melanophores developed three days later in the crushed tail but in no other place.