Pomona Collc»:e, Clarcmont, California 29 



June 19. Lighter, the spots more faded than when in the con- 

 trol. The difference between the two not so marked as on June 18, 



June 20. SHghtly lighter, more yellowish in tone. Results 

 not so distinct. 



VIII. b. June 21. Two frogs with reddish streak (June 20). 

 The streak more yellowish, now has a distinctly yellowish tone. 

 Spots lighter. Whole tone more yellow than control. 



Reversed the frogs. 



June 22. Yellowish in tone. Red streak now very yellowish. 

 Spots lighter. 



IX. June 17. 5 P. M. Two frogs, dark in color, with red 

 streaks down the back. One in blue covered jar, one control. 



June 18. 10 A. M. Frog much lighter than the control. 



The red streak along the back now sandy colored, however, 

 still with the reddish tint. Control color unchanged. Noticeably 

 darker than the one in blue. 



The frogs reversed. 



June 19. Lighter, the red streak sandy colored, same width as 

 before. Sides light grayish green. Whole tone lighter than the 

 one in the control. 



The frogs reversed. 



June 20. Lighter in tone, more greenish tinge. The red 

 streak now sandy, slightly greenish also. 



I observed some pigment cells under the microscopes. The 

 melanophores (black) were the most noticeable, although on close 

 observation yellow and bluish grey pigment cells could be seen. 



I stimulated the piece of skin with ice ; in some cases the black 

 cells seemed to expand and in others this could not be seen. Some 

 such action, however, would be necessary to cause the darkening in 

 color brought about by cold. 



The stimulations with heat were somewhat less definite than 

 with cold ; however twice the contraction of the melanophores, due 

 to a heat stimulus, was observed. 



Left the two dead frogs for six hours. When I observed them 

 again they were both remarkably lighter than they had been when 

 they were killed. 



I took a bit of their skin and observed it again. One portion 

 was much lighter and had several isolated melanophores. I cooled 

 this piece of skin with ice, then stimulated it with hot water. The 

 pigment cells seemed to expand. 



Conclusions : 



1. The tree frog changes its color in response to heat, cold 

 and changes in the color of its environment. 



