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TEXTBOOK OF ZOOLOGY 



As far as is known, the length of life of Amphibia ranges from 

 ten to fifty-two years. The larger ones, in general, seem to live 

 longer than the smaller species. Some species of toads may live 

 about thirty years, frogs probably less. 



Coloration. — Amphibians as a group are very colorful. The bright 

 green tree frog, Eyla cinerea, which makes bell-like calls from the 

 reeds and cattails in the summer months, the small grayish canyon 

 toad, Bufo pnnctatus, with its red warts, the varicolored common 

 tree frog, Hyla versicolor, with its orange groins, are but a few ex- 

 amples of beautiful species. Amphibians possess considerable abil- 

 ity to change color, and many of the tree frogs equal or surpass the 

 chameleon in this respect. 



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Fig. 260. — Melanophore from Rana temporia. A. pigment distributed m response 

 to light; B, pigment contracted. (Redrawn and modified from Noble, Amphibia of 

 North America published by McGraw-Hill Book Company.) 



Their different colors are due primarily to various combinations of 

 three kinds of pigment cells in their skin. The black melanophores 

 are branching pigment cells which may contract or expand, and, 

 when these predominate, the skin appears black or brown. Yellow 

 or red results from the action of lipophores contained in spherical 

 cells, and white from the guanophores. Green color results from the 

 reflection of light from guanin granules wherein all the light rays 

 escape absorption except the green. Different arrangements of 

 these pigment cells produce color changes which are initiated by 

 various stimuli, such as light, temperature, moisture, and the chemi- 

 cal composition of the frog's habitat. These color chajiges are 



