82 EXPERIMENTS AS TO COLORS OF FISHES. 



backgrounds to the glass vessel in which the often almost invisible morsel 

 of animal life is floating. What cannot readily be seen against a white 

 surface may become plainly apparent in front of a black one. On the 

 long middle tables (hereafter described) Mr. Agassiz has enlarged upon 

 this idea by covering them with spaces of variously colored tiles simula- 

 ting natural sea -bottoms. The clear gray does well enough for sand; 

 dark leaden gray for mud ; a mottled castile-soap pattern in brown for 

 pebbles; and dulse-green for sea- weed. It is a popular error, or, at atiy 

 rate, prevalent thoughtlessness, that sea animals pay no attention to the 

 sort of bottom underneath them as they move about. If this is true of 

 any, it certainly is not of a large number of kinds. Some are confined to 

 districts limited by one sort of bottom, because it provides their only food ; 

 others because there they are safer from harm than they would be else- 

 where; a third class perhaps from choice, or for some reason not readily 

 discernible. In any case it has been both suspected and proved that the 

 character of the bottom has great influence, particularly in the matter of 

 color, upon the fishes and others frequenting a district of mud or sand, 

 or rocky or weed-grown bottom respectively. It was in order to experi- 

 ment in this direction that Mr. Agassiz invented and provided these imi- 

 tative surfaces, which should form an artificial bottom resembling sand, 

 pebbles, etc., when the dish containing a fish or invertebrate to be de- 

 ceived should be set upon it. 



I can mention here only one of the interesting results of the experi- 

 ments. The flounder, as everybody knows, is an ill-looking, dark-c6lored, 

 flat fish, which creeps close along the bottom, and frequents for the most 

 part banks of mud, from which it is almost indistinguishable. Occasion- 

 ally the flounder resorts to sandy districts, in which case it is of a yellow- 

 ish tinge, though not otherwise different from its black neighbor of the 

 mud. Taking young flounders, Mr. Agassiz experimented upon their 

 power of changing color. Placing them upon the blackish tiles, they 

 quickly turned mud-color; moved thence to the "sand" tiles, only a few 

 moments elapsed before their leaden skins had paled to dull yellowish 

 white; transferred to the mimic "sea-weed," in less than five minutes a 

 greenish hue overspread their skins, which would have served well in 

 their native element to keep them unobserved against a mass of algas. 

 As the flounders grew older, the rapidity and facility lessened with which 

 these changes were effected, and perhaps they would altogether cease in 

 aged individuals who had never practised as turncoats; but the readiness 

 with which youngsters altered their complexions to suit their circum- 

 stances would give them high rank in partisan politics. 



