128 



The Journal of Heredity 



tion is illustrated by blue or greenish 

 eyes in man, by greenish eyes in cats, 

 and by the blue-eyed white cat. Thus 

 the blue eye has dark pigment on the 

 posterior side of the iris, while in the 

 greenish eye there is a certain amount 

 of yellow pigment on the front of the 

 iris as well. The blues seen in many 

 birds and butterflies are similarly due 

 to the presence of dark pigment under- 

 lying modifying structures, and greens 

 are produced by the addition of yellow 

 pigment. 



CREAMY WHITE FROGS 



The two color variations in the green 

 frog, with which the present paper is 

 concerned, were noticed in specimens 

 brought to the zoological laboratory of 

 the University of Pennsylvania in the 

 fall of 1916. Yellow pigment was en- 

 tirely lacking from the skin, and the 

 dark pigment was reduced to a very 

 light sepia, barely visible on the back 

 and head. The skin in genera] appeared 

 creamy white. The iris was black, 

 showing that, while the yellow pigment 

 normally present was eliminated, the 

 black was here reduced but little, if any. 

 The pupil was dark. 



This variation is apparently compar- 

 able to that described by Haecker^ in 

 the tiger salamander. He found par- 

 tially albinic forms which showed more 

 or less gray color in the skin. Yellow 

 pigment was lacking. The iris was in 

 all cases black, but, unlike that of the 

 albinic frogs, the pupil was reddish, due 

 to reduction of the dark pigment in the 

 retina. The variation described by 

 Haecker acted as a simple Mendelian 

 recessive. 



ALBINO FROGS 



The other variation in the green frog 

 was represented by a single specimen, 

 which was brought to the laboratory in 

 the fall of 1917. This was a young 

 frog lacking black pigment entirely. 

 The skin of the back, sides and head 



was clear light yellow. The only trace 

 of a darker color was a very slight 

 greenish shade in the skin about the 

 eye. The iris was clear gold; the pu- 

 pil, pink. 



Dr. Sewall Wright, in an interesting 

 series of articles on color inheritance 

 in mammals," has developed the theory 

 that there are two enzymes for color 

 production. "Enzyme I" is the funda- 

 mental enzyme, which, acting alone on 

 chromogen, produces yellow pigment. 

 "Enzyme H" has no effect on chromo- 

 gen directly, but in combination with 

 "Enzyme I" develops dark pigment. It 

 appears quite probable to me that 

 Wright's theory may be extended to 

 other groups, such as birds, amphibia, 

 and insects. 



The albinic variation in the tadpoles 

 here described, as well as in Haecker's 

 salamanders, would then be due to a 

 factor determining extreme, though not 

 complete, reduction in "Enzyme I." 

 The yellow frog, on the other hand, 

 would have "Enzyme 11" almost en- 

 tirely eliminated. If the whitish forms 

 differed from the normal variety by the 

 loss of a certain color factor, C, and 

 the yellow differed by the loss of a dark 

 color developer, D, they would recon- 

 stitute the common form when crossed. 

 Thus albino, ccDD, by yellow, CCdd, 

 gives normal, CcDd. If these were in- 

 bred, we should obtain nine (CD) nor- 

 mal, three (ccD) albinic, three (Cdd) 

 yellow, and one (ccdd) which, lacking 

 both factors, should be pure white with 

 pink iris and pupil, for cc eliminates all 

 yellow and dd eliminates all black and 

 brown. It is unfortunate that the speci- 

 mens could not be reared and tested, 

 but it has seemed worth while, in view 

 of the striking character of the varia- 

 tions noted and the apparent correla- 

 tion with color factor differences in 

 mammals, to put the matter on record. 

 The writer would be interested to hear 

 of other similar variations. 



1 Haecker, V. 1911. Allegemeine Vererbungslehre. Friedr. Vieweg & Sohn, Braun- 

 schweig. 



2 Wright, Sewall : "Color Inheritance in Alammals," Journal of Heredity, Vols, viii 

 and ix, 1917-18. 



