Ii6 A GUIDE FOR THE STUDY OF ANIMALS 



Protection, ii. Has the frog an exoskeleton ? Describe 

 the color scheme of the frog and explain how it may be 

 protective. Why are frogs brighter in spring than in fall ? 



12. Why do frogs usually live near water.' Do they 

 ever leave the vicinity of streams .' If so, when .' 



Summary. 



In what ways is the frog adapted to water life .' In 



what ways to Ufe on land.' In what respects do toads 



differ from frogs .' 



,_ ^ . , The Frog's Mouth 



Materials. 



Preserved or freshly killed frogs in dishes or shallow 

 pans of water ; forceps and a bristle. 



Observations. 



Open the frog's mouth as widely as possible and, if 

 necessary, insert a splinter to hold the jaws apart. 

 Identify the following structures : — 



Tongue. Draw it forward until the free end extends 

 from the mouth and is outspread ; observe its form, extent, 

 and attachment. 



Teeth. Find those on the jaws and on the roof of the 

 mouth. 



Nostrils. Push the bristle inward through a nostril to 

 determine its direction and extent. 



Vocal cords. These form a hard white mass in the 

 floor of the mouth, well back behind the tongue. 



Glottis, the slit inclosed beween the vocal cords, open- 

 ing into the trachea. 



Esophagus, the passage to the stomach, at the posterior 

 end of the mouth. 



Eustachian tubes, small passages outward to the ears at 

 the junction of the upper and lower jaws. 



