low of the rock, and in a quarter of an hour had resumed its former darkness.
I have recently made a number of observations upon the commoner New England frogs which show that our species possess the power of color adaptation to a large extent. The prettiest of our frogs is the common wood frog (Rana sylvatica) a pale red-dish-brown species, nearly an inch and a half long when adult (Fig. 1), but very often found in the smaller immature condition (Fig. 2). It is most commonly seen on the carpets of pine needles in the woods, where its color is precisely like that of the bed of needles on which it lives. When found on the fields and meadows away from the woods it is seldom reddish brown, being usually either light fawn color or dark brown.
A fine large wood frog was brought to my laboratory August 8th, and placed in a glass vivarium near a window. I began to study its color changes August 11th, at noon, adopting as a color standard the plates in Ridgeway's admirable Nomenclature of Colors, and the figures in parenthesis hereafter refer to those plates.
At the time mentioned the frog was light fawn color (III, 22) on the back. That night it escaped from the vivarium and wandered about the laboratory, being found the next day at 1 p. m. It was then much darker than before, the fawn color having changed to Van Dyke brown (III, 5),and the sides being dark clove brown (III, 2). Mr. Sylvatica was next placed in a dry glass Fig. 2.—Wood Frog. Immature. jar, and put in a corner of the room with a white wall on two sides of it. Three days later (August 15th, 11 a. m.) it was an extremely light fawn color on the back (III, 22, but lighter), with the sides very light drab, approaching écru drab (III, 21).
A little water was next placed in the bottom of the jar, and it was put beside a blackboard, where it was left until August 23d. The frog was then cinnamon color (III, 20). with sides dark drab. I then placed it in an open window on a whitish bottom, and the next day it was light brown. At 2 p. m., August 24th, I put it on a jet-black shelf, with black surroundings. Forty-five minutes later it was very dark, nearly mummy brown (III, 10), but darker. At
- Poulton, Colors of Animals, p. 83.
- A Nomenclature of Colors for Naturalists, by Robert Ridgway, Boston, 1886.