250 HOW DO WE CLASSIFY ANIMALS? 



PROBLEM VI. WHAT ARE THE CHARACTERISTICS OF 

 AMPHIBIANS? 



Laboratory Exercise. Adaptations in a living frog. Examine the 

 skin, note body shape, shape of head, etc., of a frog. What adapta- 

 tions for its life in the water can you find ? 



Examine the appendages. How are they adapted for locomotion? 

 Note their position in relation to the long axis of the body. What are 

 the positions of the webbed toes, and of the legs, when at rest and when 

 swimming or jumping. 



Compare the position of the eyes of the frog with those of a fish; 

 with your own eyes. In which directions can a frog see? Note the 

 eardrum just back of the eye. What evidence have you that a frog 

 can hear? 



Watch a frog catch a fly or other prey and explain how it is done. 

 Examine the mouth of a dead frog. Where is the tongue ? How is it 

 attached ? How might it be used ? Does a frog have teeth ? How 

 do you think it eats its food after catching it ? 



Look for movements of the throat, nose, and abdomen of a quiet 

 frog. Does the frog open its mouth while breathing ? Can it breathe 

 under water? Can you describe the process of breathing in a frog? 



Sense organs. The frog is well provided with sense organs. 

 The eyes are large, globular, and placed on each side of the head. 

 When the frog goes under water, a delicate fold, called the nictitating 

 membrane (or third eyelid), is drawn over each eye. The vision 

 of a frog is much keener than that of the fish. The external ear, 

 tympanum (tmi'pd-mmi), is located just behind the eye on the 

 side of the head. Frogs hear sounds and distinguish various 

 calls of their own kind, as is proved by the fact that they recognize 

 the warning notes of their mates when any one is approaching. 

 The inner ear has to do with balancing the body as it does in fishes 

 and other vertebrates. Touch is a well-developed sense. Frogs 

 respond to changes in temperature under water, and go into a 

 dormant state for the winter when the temperature of the air 

 becomes colder than that of the water. Taste and smell are 

 probably not strong sensations in a frog. 



Food-getting and digestion. The frog's mouth is large and can 

 be opened very wide. Its sticky tongue is long and flexible. It 

 is attached to the front of the floor of the mouth and can be 

 thrown out with great rapidity to secure living prey. The mouth j 

 leads into a short tube, the gullet, which widens into a long stomach. 



