Thus we find that plants and animals have in common certain processes 

 or characteristics. They take food and they grow. They are sensitive. They 

 move. They reproduce themselves. There are, to be sure, many differences 

 also, but we are considering now their common characteristics. 



Organisms Each of the distinct parts in a plant or animal is some- 

 thing more than a structural unit, like one of the bricks which make up a 

 wall. Each special structure carries on a particular kind of work, it behaves 

 in a particular way in relation to the other parts or in relation to the v/hole 

 plant or animal. It is for this reason that each of the special parts is called 

 an organ, or instrument. That is, each performs some special service or 

 "function" in relation to the whole body. Most organs or parts do some- 

 thing toward keeping the body alive. Any plant or animal that you know 

 is made up of organs. Although living things do not all have exactly 

 the same organs, the term organism is a useful one to mean any living 

 being. 



Trunk ^ 



/ 



\ 



DIFFERENT WAYS IN WHICH ORGANS CORRESPOND 



We often use the common names of the familiar parts of our own bodies for corre- 

 sponding parts of other objects, living and nonliving. The trunk and limbs of a 

 tree do correspond to the trunk and limbs of a human body, but only superficially 



Butterfly 



Airplane 



The wings of a bat, of a bird, and of a butterfly "correspond" to the wings of an 

 airplane; but in structure, development, and workings they are quite different 



18 



