34 



PRACTICAL ZOOLOGY 



branching cells which may spread out or contract, as shown in 

 Figures 183-185. When expanded, the pigment covers a larger 



area and consequently 

 gives the skin a darker 

 color. The yellow pig- 

 ment is contained in spher- 

 ical golden cells. The 

 green color results from 

 the reflection of light 

 from granules in the skin 

 through the golden cells. 

 Most of the color changes 

 are due to changes in the 

 concentration of the black 

 and yellow pigments. 



Regeneration. The 

 power of regenerating lost 

 parts is remarkably well 

 developed in many Am- 

 phibia. For example, the hand of a two-year-old axolotl was 

 cut off, and in twelve weeks a complete hand was regenerated 

 in its place. The newt has been 

 observed to regenerate both limbs 

 and tail. The frogs and toads are 

 apparently unable to regenerate lost 

 parts to any con- 

 siderable extent, 

 except in the 

 early stages. As 



FIG. 185. A pig- a general rule, FIG. 184. A pigment cell of a 



frog in state of contraction. 



the younger tad- 



( After poles regenerate limbs or tail more readily 

 than older specimens. Amphibians have a 

 distinct advantage in the possession of the power of regenera- 

 tion; for although an encounter with an enemy may result in 



FIG. 183. A pigment cell of a frog ex- 

 tended. (After Verworn.) 



ment cell of a frog 

 in a further state of 

 contraction. 

 Verworn.) 



