10 PRELIMINARY EXERCISES 



II. THE FUNCTIONS OF ORGANS 



Materials. A live locust, a frog, a chicken leg, a duck's leg, 

 wing of a sparrow, fore legs of a rabbit, a butterfly. 



Directions. (Procure several live locusts and allow them to go 

 free in the room or in a large cage.) 



A. STUDY OF A LIVING LOCUST. Study the movements 

 of a live locust. What use is made of the front legs ? 

 What are the hind legs used for ? Note carefully this dif- 

 ference in function between the fore legs and the hind legs. 

 The front legs are of most service in walking, while the hind 

 legs are used in leaping. Now note the difference in size 

 and structure between these pairs of legs. This comparison 

 shows us that a difference in the functions of organs may 

 be accompanied by a difference in the structure of those 

 organs. 



B. Now compare the hind legs of a locust with the hind 

 legs of a frog. The frog's hind legs are also used as leaping 

 organs. Is the relation of size and structure between the 

 front legs and hind legs of these animals similar? This 

 comparison shows us that a similarity of function may be 

 accompanied by a similarity of structure. 



C. The frog's leg is also used for swimming. What 

 structure between the toes fits the leg for a swimming 

 organ? Is such a structure found on the locust's foot? 

 Does the locust swim ? It would seem then, from this study 

 of the frog's leg, that an organ is structurally fitted for the 

 function it has to perform. 



D. Study the leg of a chicken and of a duck. How do 

 they differ in function ? How do they differ in structure ? 

 Are both legs especially suited to the work they are called 

 upon to perform? 



