Chap. 34 



AMPHIBIANS 



691 



> Epidermis 



! — Mucous Gland 



-"Poison" Gland 



3.^' Loose Connective Tissue 

 of Derma 



] — Pigment Cell 



,,- Subcutaneous 

 Connective Tissue 



— Muscle 



Fig. 34.9. Section of tlie frog's skin. (After Haller. Courtesy, Walter and Sayles: 

 Biology of Vertebrates, ed. 3. New York, The Macmillan Co., 1949.) 



Frogs are prevailingly green and brown, with light underparts, usually white, 

 often yellow. They may be paler or darker depending on the physiological 

 condition of the frog and its response to the environment. Although melanin 

 or black pigment occurs in the epidermis, the shifts of color in amphibians are 

 primarily due to changes in certain dermal cells called chromatophores. In 

 these cells, the pigment may be dispersed throughout the cell or concentrated 

 in its center (Fig. 34.10). There are three kinds of chromatophores arranged 

 from without inward in the following order: lipophores with yellow or reddish 

 pigment, the carotene like that in carrots; guanophores holding guanin crystals 

 (allied to uric acid) that reflect blue when against a dark background; and 

 melanophores containing brown or black pigment and always lying deepest in 

 the dermis. By their contraction or expansion, chromatophores hide others 

 from the light or expose them to it. The skin is green when the expanded black 

 pigment gives the guanin crystals the dark background against which they 

 reflect blue and the yellow pigment is expanded (Fig. 34.11). The blue and 



Fig. 34.10. Black pigment cells (melanophores) of frog skin. A, with pigment 

 dispersed. B. with pigment concentrated in the body of the cell and the processes 

 appearing shrunken. (After Hewer. Courtesy, Noble: Biology of the Amphibia. 

 New York, McGraw-Hill Book Co., 1931.) 



