66 



ANIMAL BIOLOGY 



Outward ? Backward ? Can you give reasons for the posi- 

 tion of each pair? (Suggestion: What is the use of each 

 pair?) If an organ is modified so that it is suited to serve 

 some particular purpose or function, it is said to be special- 

 ized. Are any of the legs specialized so that they serve 

 for a different purpose than the other legs ? 



The leg of a grasshopper (as of all insects) is said to 

 have Jive parts, all the small parts after the first four parts 

 being counted as one part and called the foot. Are all 

 the legs similar, that is, do the short and long joints in all 

 come in the same order ? Numbered in order from the 



Fig. 109. — How a Grasshopper 

 Walks. 



Fig. iio. — How a Spider 

 Walks. 



body, which joint of the leg is the largest, — the first, sec- 

 ond, third, or fourth ? Which joint is the shortest ? The 

 slenderest? Which joint has a number of sharp points or 

 spines on it ? Find by experiment whether these spines 

 are of use in walking (Fig. 106). Jumping? Climbing? 

 In what order are the legs used in walking ? How many 

 legs support the body at each step ? 



All animals that have ears have ways of communicating 

 by sounds. Why would it be impossible for the grasshop- 

 per to have a voice, even if it had vocal cords in its 

 throat ? The male grasshoppers of many species make a 

 chirping, or stridulation, by rubbing the wing against the 

 leg. Look on the inner side (why not outer side ?) of the 



