34 LIFE DEPENDS ON ADAPTATIONS 



for example, such a simple act as walking. Simple, but 

 is it ? So many parts of the body act together muscles, 

 bones, nerves, heart, lungs, sense organs, and the master 

 of them all, the brain that what seems a simple act 

 is found to be very complicated. You cannot with the 

 little knowledge you have at this time explain such an 

 act. But take something you can see and try to find 

 adaptations there. Have you ever thought how wonder- 

 fully your hand is adapted to the work of holding ob- 

 jects, such as a pen or pencil? You know in a general 

 way that it is a complicated mechanism, but do you know 

 how it is built ? For example, we have a bony framework, 

 in which the individual bones are held loosely together 

 in order to allow movement. But these bones are also 

 bound together tightly enough so that they cannot get 

 out of place. Not only are they held together, but each 

 is separated from its next neighbor by a pad of soft elastic 

 cartilage which gives a certain amount of play to the 

 whole hand skeleton. Then each bone has attached to 

 it scores of small, elastic bundles of muscles, some thirty- 

 one in number, which will expand and contract. These 

 muscles work in pairs, one relaxing as its partner con- 

 tracts, and since they are attached to the bones, they give 

 movement to them. But think of the numbers of muscles, 



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What kinds of food would you think these birds eat ? Can you describe the kind 

 of feet each of the above birds would have ? 



