tEiUered at the Posi-Offlce of NewTfork, N.Y., as Second-Class Matter.J 



A WEEKLY NEWSPAPER OF ALL THE ARTS AND SCIENCES 



Eighth Year. 

 Vol. XV. No. 374. 



NEW YORK, Apjkil 4, 1890. 



Single Copies, Ten Cents. 

 .$3.50 Peb Year, in Advance.. 



THE COLOR OF FISHES. 



The skin of a fish, upon the structure of which its color 

 depends, consists of two layers, — the outer, or epidernnis, 

 delicate, transparent, and not supplied with blood-vessels; 

 the inner, the corium or dermis, laminated and elastic, vary- 

 ing in thickness in difiFerent species and in different parts of 

 the body, and permeated by blood-vessels and nerves. Be- 

 tween the skin and the underlying muscles is a layer of 

 loose connective tissue, often loaded with fat, especially in 

 the mackerels and salmonoids and in the herring tribe. In 

 the menhaden' this layer is thick, hard, and blubber-like. 



The scales are modifications of the dermis, and are ordi- 

 narily thin, transparent, horny plates, with rounded quad- 

 rangular outlines, which are partially embedded in folds or 

 pockets in the dermis, and covered by the epidermis, through 

 which, however, their tips protrude. The scales are usually 



SECTION OF THE SKIN OP A FISH. 



a, epidermis; 6, scales; c, dermis. 



imbricated, overlapping each other like the shingles on a 

 roof, but are sometimes separated and embedded, and partly 

 hidden in the skin, as in the eel. 



In fishes which live near the bottom and among the rocks, 

 such as the sea-bass, red snapper, sheephead, and perch, the 

 scales are usually thick, hard, closely imbricated, and deeply 

 set in their sheaths, forming an impermeable coat-of-mail. 



In fishes which live in the mud, such as the tautog, the 

 burbot, and the carp, the scales are usually covered by thick 

 layers of epidermis and mucus. 



In fishes which swim free and far from shore, such as the 

 herrings and the lake white-fishes, the scales are attached 

 merely by a small area of their rims, and, being but slightly 

 covered with epidermis, are easily rubbed off. Scales thus 

 removed are in many fishes easily renewed. 



The smooth polished surface of the closely set scales offers 

 little resistance to the motion of the fish as it glides swiftly 

 through the water. 



The exposed surface of the ordinary fish-scale is usually 

 covered with a thin silvery coating, which derives its brilliant 

 metallic lusLi-e from the presence of numerous crystals of a 

 combination of guanin and lime. 

 This coating may readily be loosened 

 and rubbed off, and in one European 

 fish, the bleak or ablette, a member 

 of the carp family, the crystals are 

 sufficiently abundant to become the 

 COATING OF A FISH-SCALE ^oavcB of thc metalHc pigment known 

 (MAQNiFiED 600 times;). lu thc ai'ts as essence cV Orient, or 

 argentine, which is used to impart a 

 nacreous lustre to ,the glass globules sold under the name of 

 "Eoman pearls." When the silvery coating is absent. 



CRYSTALS FROM THE SILVERY 



scales are lustreless and transparent, as in the smelt, the 

 abdominal cavity of which, however, has a brilliant silvery 

 lining composed of the same substance. 



The colors of fishes are very varied, and often exceedingly- 

 brilliant and beautiful. " Aucune classe d'animaux n'a ete- 

 aussi favorisee a cet egard," says Lacep6de; "aucune n'a 

 re9u une parure plus elegante, plus variee, plus riche; et 

 que ceux qui ont vu, par exemple, des zees, des chetodons, 

 des spares, n^ger pres de la surface; d'une eau tranquiUe et 

 reflechir les rayons d'un soleil brillant, disent, si jamais 

 I'eclat des plumes du poeon et du colibri, la vivacite dur 

 diamant, la splendeur de Tor, le reflet des pierres precieux, 

 ont ete meles a plus de feu, et ont renvoye a Toeil de I'ohser- 

 vateur des images plus parfaites de cet arc merveilleusenient 

 colorie dont I'astre du jour fait souvent le plus bel ornament 

 des cieux." 



The colors are often due to a simple arrangement of pig- 

 ment cells, placed at different depths in the skin ; but those- 

 changeable and brilliant hues which constitute the greatest" 

 beauty of fishes are dependent, as Poucliet and others have- 

 shown, upon two very dissimilar causes. 



One of these, which may be well observed in the scales of 

 the herring, shad, or mackerel, is a true iridescence, similar' 

 to that seen in the pearl or in antique glass, and due to the" 

 refraction of the rays of light as they glance off the surfaces 

 of thin plates or ridges in the scales. This is called " lamel- 

 lar coloring." There are certain bodies called " iridocy tes " 

 (rainbow plates) embedded in the epidermis which have an 

 important function, it is said, in this iridescent play of 

 colors. 



The coloration is, however, chiefly dependent on the ar- 

 rangement of the pigment-cells, or chromatophores, which; 

 lie in the lower strata of the epidermis. These are black, 

 yellow, and red; the latter, according to Pouchet, being 

 capable of dimorphic changes into blue and green. The 

 combinations of the various-hued chromatophores with the 

 metallic crystals of silver, the white of the bony scale-plates 

 showing through the epidermis, and the iridocytes already 

 referred to, produce the coloration of every kind of fisfr. 



An embryonic fish is colorless; but the pigment-cells oi 

 black, yellow, and red soon begin to appear, as is shown in 

 Alexander Agassiz's beautiful plates of the early stages of 

 flounders and other species, published in the "Bulletin of 

 the Museum of Comparative Zoology." When the black 

 pigment predominates, the color is sombre, as in the adult 

 tautog, Tautoga onitis. A slight admixture of yellow gives 

 the bronze-like hue of the eel, and a little more of the same, 

 results in the brighter green of the black-bass, the blue-fish,, 

 and the cunner. In all of these there is a sprinkling also of 

 red, giving the warmer brownish greens so often seen in- 

 these species. Red pigments intermixed with black give the 

 dingy browns of the carp, the sculpins, and some of the ca^ 

 fishes. When the yellow and red outnumber the black cells, 

 there result the tawny colors of the sand-dabs, the sun-fishes^ 



