SCIENCE. 



[Vol. XV. No. 374 



the cusks, and the ling, and of some varieties of the cod. 

 Red chromatophores alone cause the brilliant scarlet of the 

 red snapper and the rose-flsh, and, when these are inter- 

 spersed with black, the deeper colors of the mangrove snap- 

 per and the ruddy variety of the sea-raven. When the 

 chromatophores begin to segregate into separate groups ac- 

 cording to color, the result is the formation of bands, stripes, 

 spots, and shadings infinite in their possibilities of mutation 

 and combination, and quite beyond the power of -words to 

 describe. 



The entire absence of chromatophores results in albinism. 

 I have already called attention to the curious albino haddocks 

 occasionally taken on our coast. Sometimes these are of a 

 light golden color, and are in what Giinther calls a state of 

 "incipient albinism," the dark pigments having changed 

 into yellow. This has been observed also in flounders, 

 carps, and eels, and in the gold-fish, which in its native 

 ha,unts in China is a dull green. The golden orfe and the 

 golden ide have become permanent in a state of domestica- 

 tion. The silver-fish, a form of gold-fish, is an example of 

 still more complete albinism; and a combination of the two 

 conditions is very common in the breeding-ponds of the 

 United States Fish Commission. 



'The blind-fish of Mammoth Cave, Amblyopsis spelmus, is 

 •^n illustration of permanent adaptive albinism; and in the 

 abysses of the sea, where the light is very scanty, many 

 flashes appear to remain permanently in this condition. 



Adaptive coloration seems to be possible in quite another 

 way, through the secretion of pigment-cells, which perma- 

 nently change the color of the fish to make it harmonize 

 with that of the bottom upon which it lives. On certain 

 ledges along the New England coast the rocks are covered 

 with dense growths of scarlet and crimson seaweeds. The 

 cod-fish, the cunner, the sea-raven, the rock-eel, and the 

 wry-mouth, which inhabit these brilliant groves, are all 

 colored to match their surroundings; the cod, which is nat- 

 urally lightest in color, being most brilliant in its scarlet 

 hues, while the others, whose skins have a larger original 

 supply of black, have deeper tints of dark red and ruddy 

 brown. These changes must be due to the secretion of a 

 special supply of red chromatophores. It has occurred to 

 me that the material for the pigmentary secretion is probably 

 derived indirectly from the algse, for, though the species 

 referred to do not feed upon these plants, they devour in 

 immense quantities the invertebrate animals inhabiting the 

 same region, many of which are likewise deeply tinged with 

 red. Possibly the blacks and greens which prevail among 

 the inhabitants of other colored bottoms are likewise de- 

 pendent upon coloring-matter which is absorbed with the 

 food. Giinther believes that the pink color in the flesh of 

 the salmon is due to the absorption of the coloring-matter 

 of the crustaceans they feed upon. Spoonbills and flamin- 

 goes lose the brilliant pink tints of their feathers after long 

 confinement in menageries, and it is customary for Euro- 

 pean zoological gardens to send them to the garden at 

 Rotterdam to be recolored. It is not known how this is 

 done, but it is supposed that they are fed upon some red- 

 hued crustacean there obtainable. 



The brilliant coloration of many kinds of fishes during 

 the breeding-season may possibly have a relation to sexual 

 selection ; indeed, this can scarcely be doubted by any one 

 who has observed the peacocking moments of male fishes. 

 It has also a physiological significance which it is not dif- 

 ficult to comprehend. The increased brilliancy is usually 

 most manifest in those parts of the body which lie close to 



the reproductive organs, in the belly, which is often flushed 

 and vivid in color, in the ventral fins, and in less degree in 

 the sides of the body and the posterior and lower parts of 

 the head. The Entire vascular system is in a condition of 

 extreme activity at this time, as is evident from the manner 

 in which outgrowths of the head and teguments are so 

 rapidly developed. Every pigment-cell is receiving an un- 

 usual supply of blood, and its more abundant nutrition is, 

 in part at least, the cause of its brilliancy. 



If an abundant supply of blood results in an increase in 

 brilliancy, its withdrawal from the teguments, on the other 

 hand, causes an immediate decrease. I have often watched 

 the large brightly striped " groupers," Epinephelus striatus, 

 confined in the crystal fish-pools in Bermuda. When one 

 of these had swallowed a large morsel of food, its color be- 

 came almost instantly lighter and duller. This was evi- 

 dently the result of the rush of blood to the stomach, to take 

 part in the work of digestion: in like manner a man's face 

 often becomes paler after he has eaten a hearty dinner. 



The dulness and pallor in the color of fishes after death are 

 due to the absence of living blood from the chromatophores. 

 If, however, a fish not long dead is placed in the sun, its 

 color will soon become almost as deep and bright as in life. 

 In a few seconds it fades again, and cannot again be brigh- 

 tened. 



This phenomenon leads to the consideration of another 

 peculiarity in the arrangement of the pigment-cells, which 

 renders rapid changes in hue possible in certain species. 

 In these the pigments are associated with oily matter, and 

 are arranged areolce, which favor their approach toward or 

 retreat from the surface of the skin. The accompanying 

 diagram, drawn by Profes-' 

 sor Benecke, shows how they 

 may sometimes show as 

 small, irregular spots upon 

 the skin, and soon after be- 

 come conspicuous star-shaped 

 markings with far-reaching 

 arms. Such changes may 

 be effected by stimulation of 

 various kinds, and even by 

 the reflex action of the nerves 

 under the influence of impres- 

 sions of color received by the 

 eye of the fish. 



Every angler knows that trout inhabiting stagnant pools 

 or dark bottoms are deep-colored, while those from deep, 

 sunny waters are brighter. The same is true of many other 

 fishes. I have often seen the common flat-fish change its 

 color to that of the gravel and sand in which it was trying 

 to hide, the hue varying as rapidly as that of the landscape 

 when the sunlight is suddenly cut off by a passing cloud. 



These changes of color are directly connected with the 

 impressions of color received by the eye, and brought about 

 by the reflex action of the nervous system. In no other 

 way can changes such as those already referred to in floun- 

 ders be accounted for. I have seen the tropical squid in 

 Bermuda change color rapidly, and at will, while being 

 pursued. This was evidently through the influeuce of emo- 

 tion or fear, since it can hardly be supposed that there was 

 definite purpose in the act; which, however, seemed at first 

 sight to be intended to baffle its pursuers. 



Pouchet experimented with young turbots, and found 

 that if their eyes were blinded they did not change, thus 

 proving that the color-cells were under the control of the 



CHROMATOPHORES VARIOUSLY 

 EXPANDED. 



