398 



COLLEGE ZOOLOGY 



Color and color changes 



The colors in the skin of amphibians are 

 due to scattered pigment granules in the 

 epidermis and to pigment cells in the dermis. 

 The latter are usually brown, black, yellow, 

 or red and are contained in cells called 

 chromatophores. The power of changing 



color is possessed by most amphibians, and 

 especially by frogs. The common leopard 

 frogs are supplied with black pigment cells 

 called melanophores and with interference 

 cells that contain whitish crystals, golden 

 pigment cells, and sometimes red pigment 

 cells. 

 The black melanophores are branching 



OJI 



Melanophore with pigment 

 dispersed throughout cell 



Pigment beginning 

 to concentrate 



Pigment concentrated 

 in body of cell 



Figure 268. Stages in the changes of pigment-bearing cells (melanophores) in the skin of 

 the frog. The color variation from the fully expanded to the completely contracted melanophore 

 is black to gray. 



cells as shown in Fig. 268. When the pig- 

 ment is dispersed, it covers a larger area and 

 consequently gives the skin a darker color. 

 When the pigment is concentrated the skin 

 becomes lighter. These changes in the color 

 of the skin are shown in Fig. 269. The yel- 

 low pigment is contained in spherical golden 

 cells. There is no green pigment; the green 

 color results from a combined effect of light 

 reflected from the granules of the interfer- 

 ence cells and the yellow pigment through 

 which the light passes. Most of the color 

 changes are due to changes in the concentra- 

 tion of the black and yellow pigments. 



Color changes are brought about primar- 

 ily by a hormone called intermedin,* which 

 is secreted by the intermediate lobe of the 

 pituitary gland. Intermedin causes a dis- 



* Intermedin causes dispersion of pigment in the 

 melanophores of fishes, amphibians, and reptiles, but 

 appears to have no effect on the pigmentation of 

 warm-blooded birds and mammals. 



persion of pigment granules. Light is the 

 chief stimulus; it acts through the eye. Ex- 

 perimentally blinded frogs show a reduced 

 capacity to change color. In a bright light 

 the skin of the frog becomes light in color, 

 whereas in the dark it changes to a darker 

 hue. 



Changes in color are due to both external 

 and internal conditions; temperature is an 

 important external factor. When the tem- 

 perature is raised, the pigment becomes 

 more concentrated, and the skin changes to 

 a lighter color. When the temperature is 

 lowered, the pigment becomes expanded, 

 and a darker color results. It is evident that 

 changes in the skin color of the frog are in 

 part due to a hormone (intermedin) and in 

 part to the nervous system. Usually the 

 color changes are such as to cause the frog 

 to resemble more closely its surroundings; 

 thus it becomes less conspicuous and is pro- 

 tectively colored. 



