OF ARTS AND SCIENCES. 15 



of coerulescence by interference of light (as shown by Briicke), of 

 solid particles more or less analogous to excessively thin laminre. By 

 simple combinations of the action of the red, yellow, and black chro- 

 matophores with the iridocytes are obtained all the colors which we can 

 produce in Fishes, Reptiles, Crustacea, Mollusks, &c. ; these colors re- 

 sulting mainly from the expansion near the surface, or retraction into 

 an inferior layer of the black chromatophore, which, thus mixed with 

 the yellow and red, or with the iridocytes, at greater or less depths, 

 suffice to produce all the variations of coloring of our young Flounders. 

 An examination of Plate VIIL, showing the changes of coloring pro- 

 duced upon young Flounders when placed upon differently colored 

 bottoms, will readily show the process by which the different colora- 

 tions are produced. 



In the Flounders, after the eyes have passed to one side, the 

 connection between the impression produced on the retina and the 

 blind side becomes less and less distinct, until eventually a complete 

 paralysis of the nerves affecting the chromatophores takes place ; and 

 little by little the blind side thus becomes white with advancing age. 



The pigment cells are of three colors, — black, yellow, and red (PI. 

 VIII. fig. 6) : the black expand nearest the surface, the yellow and 

 red varying greatly in their position, according to the species. The 

 black cells are all more or less dendritic when expanded, concentrating 

 to a mere dot when wholly contracted. The proper mixture of the 

 three colors in various degrees of expansion or contraction, combined 

 with the suitable pattern of position, enables the Flounders to imitate 

 so admirably the general effect of the ground upon which they are 

 accustomed to feed, be it either sandy, gravelly, or muddy. So true is 

 this, that often only a most practised eye could detect them, as, with 

 the head slightly raised, the eyes starting out of their sockets far above 

 the surface of the head, they turn actively in all directions, seeking for 

 prey, or trying to escape the notice of their enemies. The rapidity 

 with which they produce this change of color is quite striking ; and, 

 although it was well known that many fishes had the power to change 

 gradually the tint of the body, it had not been noticed that it could be 

 effected rapidly, and apparently at will, before it was recognized 

 by Pouchet. I have not unfrequently removed the jar containing a 

 young Flounder (PI. VIII. fig. 2) from a surface imitating a sandy 

 bottom to one of a dark chocolate color, and in less than ten minutes I 

 have seen the black pigments obtain such a preponderance (PI. VIII. 

 fig. 1) that it would hardly have been possible to recognize in the dark, 

 almost black fish the young Flounder, whose yellowish-gray speckled 



