438 FRANCIS B. SUMNER 



curred in the next six days, at the end of which it was photo- 

 graphed, after being transferred to a jar having a black bottom and 

 white walls (fig. 8d). By this time, however, the fish appeared 

 to have wholly lost its power of response, for it changed but 

 slightly during a stay of six days in this jar, six days in a jar whose 

 walls and bottom were both black, five days upon a coarse reddish 

 gravel, and two days upon the dark, mixed sand.^- 



Similar experiments were tried with a number of specimens, but 

 several of them became blind or otherwise diseased before decisive 

 results were obtained. The most pronounced success was achieved 

 in the case of fish no. 9. In fig. 9a, this fish is shown lying upon the 

 bottom of dark mixed sand, on which it had been kept for two 

 days."*^ The tests to which it was further subjected were as follows. 



It was first put into a dish 16 cm. in diameter and 7 cm. deep, 

 having the vertical walls painted black, and the bottom covered 

 with fine gravel, cemented in place with plaster of Paris. ^^ The 

 length of the fish was about 15 centimeters, and it must have 

 covered from one-third to one-half of this bottom, while the head 

 must at all times have nearly or quite touched the black vertical 

 wall of the jar. In the course of a few hours, notwithstanding, the 

 fish had changed somewhat in the direction of harmony with the 

 gravel, while fig. % shows its condition on the following day. The 

 appearance is certainly quite different from that manifested upon 

 the sand, and is not ill-adapted to the new bottom, though it is 

 recorded as '^somewhat darker in appearance than the gravel, 

 and gravel pattern not particularly good." 



Transfer to a larger jar (20 cm. diameter, 12 cm. high), also 

 with black walls and gravel bottom, did not result in any appre- 

 ciable change, but upon removal to a large open tank, having 

 gravel of the same sort at the bottom, the fish resumed the maxi- 

 mum degree of resemblance within a few hours. The animal was 



« Cf. p. 433, above. 



*^ It had previously been well adapted to the fine gravel. After transfer to sand, 

 it changed considerably within an hour or less, and the maximum effect probably 

 resulted within a day or less. 



" This was done in order to prevent the animal from covering itself with the 

 gravel. 



