Whiting: Color Variations in the Green Frog 



127 



This result is not merely a selfish 

 benefit to the higher races but a good to 

 the world as a whole. The object is to 

 produce the greatest number of those 

 fittest not "for survival" merely but 

 fittest for all purposes. The lower 

 types among men progress, so far as 

 their racial inheritance allows them to, 

 chiefly by imitation and emulation. 

 The presence of the highest develop- 

 ment and the highest institutions among 

 anv race is a distinct benefit to all the 



others. It is a gift of psychological 

 environment to anyone capable of ap- 

 preciation. 



It is important, therefore, that noth- 

 ing in the constitution of the League of 

 Nations should limit the right of any 

 nation to decide who shall be admitted 

 into its life; for, as Le Bow says, a 

 preponderance of foreign elements de- 

 stroys the most precious thing it 

 possesses — its own soul. 



TWO STRIKING COLOR 



VARIATIONS IN THE GREEN FROG 



P. W. Whiting 

 Franklin and Marshall College, Lancaster, Pa. 



IT IS well known to every student of 

 pond life that the common green 

 irog, Rana ciamitans Latnelle, snow 

 many variations in color. Typically, 

 the coloring is bright metallic-green on 

 head and shoulders and dusky oiive, 

 more or less spotted, posteriorly. The 

 throat is orange-yellow in the male, 

 white in the female. 



The dark coloration of frogs is due 

 to a layer of black pigment cells under 

 the epidermis. Under the influence of 

 various stimuli, these cells have the 

 power of changing shape. Expansion 

 produces a dark color, contraction a 

 dilution effect. Alary C. Dickerson, in 

 The Frog Book, explains the produc- 

 tion of green color as follows : 



"Green color is not produced directly 

 by a pigment, but as the result of black 

 and yellow pigments and a structure, 

 namely, the so-called interference layer. 

 This is a single layer of polygonal cells 

 between the epidermis and the black 

 pigment layer. These cells contain 

 minute yellow particles, which crowd 

 to the sides of the cells next the epi- 

 dermis. If these cells were empty, the 

 result wov;ld be simply that the black 

 pigment layer would be farther from 

 the surface and would be seen througli 

 the interference layer. This would 



make the color appear blue instead of 

 black, giving the ordinary color phe- 

 nomenon of dense media, as seen in the 

 color of the sky {i. e., all the light waves 

 of great wave lengths are absorbed and 

 only those of short lengths are re- 

 flected). When the interference cells 

 contain yellow, the blue is seen through 

 the yellow, and the resultant color is 

 green. 



"The green color thus produced may 

 be more blue or more yellow, and may 

 change to brown when the black pig- 

 ment cells expand greatly and press 

 close about the cells of the interference 

 layer, thus diminishing the density. A 

 fragment of the outer skin of a green 

 tree frog, examined from underneath, 

 of course appears black, because we are 

 looking directly at the black pigment 

 layer. The same piece looked at from 

 above and against the light appears 

 brown, but examined from above with 

 light from above it appears green and 

 shows the polygonal cells of the inter- 

 ference layer. 



"Therefore, frogs that have the inter- 

 ference layer and black and yellow pig- 

 ments appear green or brown, and can 

 change from one to the other with 

 great rapidity." 



The same [principle of color produc- 



