COLOR CHANGES AND ADAPTATION IN FISHES. 1 85 



Nearly all of the specimens used in this experiment had been for some time in a 

 white aquarium and were uniformly very light in shade with little or no color. Very 

 soon after they were put on the different bottoms, in some cases almost immediately, 

 the shade, the color, and the pattern in the skin began to change, and within five minutes 

 a striking difference could be clearly seen between the individuals on the different 

 bottoms, although there was at this time in most cases very little resemblance between 

 the fish and the background. Gradually, however, they came to look more and more 

 like the background until, in the course of several days, in some cases in a few hours, 

 in others a number of weeks, it required more than casual observation to locate the 

 animals. This was particularly true with reference to those on the different kinds of 

 sand. But on all of the bottoms there was a most remarkable similarity between the 

 fish and the background in color as well as in shade and configuration. Some features 

 of this resemblance are well represented in the photographs. (PI. xix, xx, fig. 1-7.) 



In taking these photographs, as well as all of the others, and also the autochromes," 

 referred to later, especial precautions were taken to get the illumination of the object, 

 depth (2 to 3 cm.) and character of the water, and the exposure and treatment of the 

 plates in all cases as nearly alike as possible. The exposures were all made in front of a 

 large window, in strong diffused sunlight.* In each case, before the exposure was made, 

 the specimen to be photographed was kept for some time in a crystallizing dish or a 

 shallow box in the place in which it was photographed. In these retainers the fish were 

 fed and supplied with running water. (Fig. i, p. 186.) They were observed frequently 

 and gently touched and stroked until they became thoroughly accustomed to their new 

 environment. As previously stated, however, these creatures are readily tamed and 

 many of them, in a surprisingly short time, can be pushed about the aquarium and 

 even picked up without showing any marked effect. Moreover, the camera was often 

 adjusted and kept in place for some time before making the exposure. In short, the 

 animals were given a preliminary course of training. 



Such precautions are of the greatest importance in work of this sort, for the ap- 

 pearance of the skin changes greatly if the animals are disturbed. (Fig. 21, 22.) In 

 animals just brought into the laboratory the slightest movement about the aquarium 

 usually induces such changes; merely directing one's eyes toward them is often sufficient. 



No changes, by retouching or otherwise, were made in any of the figures. Standard 

 Orthenon plates were used almost exclusively. Moreover, careful observ^ations were 

 made and recorded in each case at the time the photograph was taken, and in printing 

 these descriptions served as a guide in attempting faithfully to reproduce the various 

 shades and patterns assumed by the fish. Thus the inaccuracies in reproduction were 

 reduced to such an extent that I feel certain they are of no serious consequence, espe- 

 cially in conclusions resting upon a comparison of the skin with the background or of 

 the skin in individuals under different conditions. 



By referring to these photographs it will be clearly seen that the light and dark 

 areas in the skin are relatively large in the individuals on coarse-grained bottoms and 

 relatively small in those on the fine-grained bottoms, and that the shade of the skin 

 in general corresponds well with that of the background. But the adaptation in color, 



« The technical work connected with the photographs and autochromes was done by F. H. Harper, to whom I am under 

 great obligations for apparatus as well as for expert service. 

 & Some autochromes were later taken in direct sunlight. 



