HISTOLOGICAL BASIS OF ADAPTIVE COLORS IN PARALICHTHYS ALBIGUTTUS. 1 3 



proves conclusively that this conclusion is correct. The work of Pouchet (1876), 

 furthermore, indicates that the chromatophores are under the direct control of the 

 sympathetic nervous system. Ballowitz (1893) described a dense network of nerve 

 fibers, presumably sympathetic in character, surrounding the chromatophores in the 

 skin of certain fishes. The experimental work of Frisch (1910) on trout and minnows 

 tends to show that the nerve fibers which control the chromatophores pass out at a precise 

 level from the spinal cord into the sympathetic trunks and pass with them anteriorly 

 and posteriorly. Frisch claims, furthermore, to have demonstrated a special center in the 

 anterior end of the medulla whose stimulus brings on a contraction of the chromatophores. 

 In sections of the skin of Paralichthys albiguitus prepared by the pyridine-silver 



method the writer observed both medullated and 



nonmedullated nerve fibers which vary greatly in e 



caliber. The medullated and the larger nonmedul- 

 lated fibers were never observed in relationship 

 with the chromatophores. However, many of the 

 smaller nonmedullated fibers could be traced to 

 their terminations on chromatophores (text fig. 5). 

 These fibers do not form a dense network about 



chromatophores, as described and illustrated by F-C-S-Cameraludda drawings of melanophores 

 ^ •' and nerve fibers associated with them in a sec- 



Ballowitz (1893), but run more or less directly from tion of the skin of Paraikkthys Mi^ttus pre- 

 the fiber bundles in the skin to their termination on p'"^'* *»' ">« pyrfdine-siiver method. (., epi- 



dennis; wt, melanophores; », nerve fibers.) 



the chromatic organs. The nonmedullated character 



of these fibers does not prove them to be sympathetic. However, this character, together 



with the small caliber of the fibers, strongly suggests that they are sympathetic in nature. 



DETAILED STUDY OF CHROMATOPHORES AND GUANOPHORES IN SKIN OF FISH ON GIVEN 



BACKGROUNDS. 



INTRODUCTION. 



The experimental work of Mast proves conclusively that in members of the genus 

 Paralichthys the skin simulates the background in color as well as in shade and pattern. 

 In his summary he says : 



The range of changes in the skin in members of this genus is most remarkable. On a white back- 

 ground they become almost ptire white, on a black background nearly black, and on gray backgrounds 

 of various shades they become gray of very nearly the same shade. On blue, green, yellow, orange, pink, 

 or brown of various hues they assume a color remarkably similar to that of the background. Reds of 

 various tints and shades, however, are not very accurately simulated, but the color produced in the skin 

 by each tint or shade of red is different from that produced by any other color and very different from that 

 produced by gray regardless of the intensity.^ 



In the present investigation specimens of Paralichthys albiguttus were kept on back- 

 grounds of given shades and colors until their skin simulated the shade or color of the 

 background as nearly as possible. In general the shades and colors used were the same 

 or similar to those used by Mast. The color-producing elements in the skin of these 

 specimens, as well as of specimens newly taken, were studied microscopically in order 

 to determine as accurately as possible what factors are involved in the production of 

 given shades and colors. 



" Bulletin Bureau of Fisheries, vol. xxxiv, 1914, p. 12%. 

 69571°— 18 2 



