70 THE NATURE STUDY COURSE. 



body and the length and strength of the hind legs are adapted 

 to jumping or hopping. Put a frog in water and observe how 

 it swims. 



Its Structure, — Notice the color, dampness and smoothness 

 of the skin. Obtain two similar frogs, one of which keep in 

 a jar laid in the shade over, or wrapped in, a black cloth, and 

 lay the other in a bright place over a white cloth or paper. 

 After a time observe the difference in the color of their skin. 

 What advantage may a change of color be to a frog 1 



Measure the lengths of its body and those of its front and 

 hind legs. Compare them. Observe its position when resting. 

 Notice its four separate fingers and its five webbed toes. 

 What use is the web? 



How wide can it open its mouth ? What is the use of the 

 wide gape 1 Can it breathe when its mouth is open ? What 

 is the shape of its tongue ? What advantage is it that the 

 tongue is free behind 1 



Has it a bright eye 1 Describe the eye. Touch the eye. 

 Study the eye-lids. Infer whether the eye is surrounded by a 

 bony orbit. Touch the eye when the mouth is open. Notice 

 its ear-drum below and back of the eye. Observe the nostrils. 



Feel whether it has ribs. Name the bones that you can 

 locate by feeling without hurting the animal. Compare the 

 bones of its hind leg with those of a human leg or a cat's leg. 

 Where is its knee ? Where its ankle ? 



Circulation of Blood. — If a compound microscope is avail- 

 able it is easy to show the pupils one of the most beautiful and 

 instructive microscopic objects, namely, the circulation of blood 

 in the web of a frog's hind foot or in the nearly transparent 

 margin of a tadpole's tail. One who has seen this wonderful 

 sight a hundred times will turn to it again with interest. The 

 simplest way to exhibit the phenomenon is to have one child 



