522 



COLLEGE ZOOLOGY 



Rana palustris, the pickerel frog, inhabits the brooks and 

 ponds of eastern North America, and is often found also in 

 fields and meadows. It reaches a length of three inches. 



Suborder 3. COSTATA. --The five genera 

 and eight species of SALIENTIA included 

 in this suborder all belong to the single 

 family DiscoGLOSsm^E. Only one species 

 occurs in North America ; this is the 

 American discoglossoid toad, Ascaphus 

 truci, of which only a single specimen 

 from Humptulips, Washington, is known. 

 An interesting European species is the 

 obstetrical toad, Alytes obstetricans (Fig. 

 436). The male of this toad carries the 

 FIG. 436. The ob- egg strings with him wound about his 



stetrical frog, Alytes ob- 

 stetricans ; male, with hind limbs, and when the tadpoles are 



string of eggs. (From rea d y to emerge, takes to the water and 



Sedgwick's Zoology, after 



Claus.) allows them to escape. 



4. GENERAL REMARKS ON AMPHIBIA 



Color and Color Change. - - The pigments in the skin of 

 AMPHIBIA are diffuse or granular. The latter are usually brown, 

 black, yellow, or red and are contained in cells called chromat- 

 ophores. The power of changing its colors is possessed by most 

 AMPHIBIA, but especially by the frogs. These are supplied with 

 black pigment cells, interference cells, golden pigment cells, 

 and sometimes red pigment cells. 



The black chromatophores are branching cells which may 

 spread out or contract, as shown in Figure 437. When ex- 

 panded the pigment covers a larger area and consequently gives 

 the skin a darker color. The yellow pigment is contained in 

 spherical golden cells. The green color results from the re- 

 flection of light from granules of guanin 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. 



