Body Covering 35 



have been dizzy. They were put on pale backgrounds and on 

 dark backgrounds, on sand and on mud, on fine gravel and 

 on coarse gravel, on black-and-white checker-boards, and 

 on black polka-dots on a white field. One poor fish was even 

 kept in a glass-bottomed tank under which a checker-board 

 slowly but continually revolved. 



To eliminate all question of the optical illusions of the 

 observers, careful photographs of each experiment were taken. 

 And when the evidence was all in, there was no room left for 

 argument. The resemblances between the patterns of the 

 fishes' skin and the backgrounds on which they lay were 

 unquestionable, even in the case of the merry-go-round. Not 

 that the animals had been able to reproduce polka-dots and 

 squares on their skinj these actual shapes were beyond them. 

 But in every case, the general eflFect of the skin-pattern was 

 remarkably close to the general effect of the background. If 

 it was white, the skin was almost colorless j if it was black, 

 the skin was very dark. If it was made up of very small black- 

 and-white squares, or polka-dots, the skin had a fine-grained 

 light-and-dark pattern j if it was made up of large checker- 

 boards or polka-dots, the skin had a correspondingly coarse 

 light-and-dark pattern. Some of the photographs which 

 were taken are reproduced here (Plate III), and give a better 

 idea of what happened than any amount of description. 



It was also found that, in addition to being able to adapt 

 their skins to various shades of light and dark and to various 

 degrees of coarseness of pattern such as might be found in 

 their own habitats, some of these fishes were able to simulate 

 different colors, blues, greens and purples, which they would 

 never meet under natural conditions. Other points were 

 brought out in the course of the experiments which add sig- 

 nificance to the whole picture. 



In the first place, it was found that individual fish varied 

 greatly in their color-changing abilities. Some fish changed 



