96 



The Living Thijigs of the Earth unit 



no Coins 



60 U.S. Coins 



Fig. 126 



The diagram shows you something 

 else. The oftener you subdivide, the 

 smaller the mimber of specimens or in- 

 dividuals in each successive grouping. For 

 example, you start with 1 10 coins but the 

 number of United States coins is only 60. 

 In the next grouping there are 16, 14, and 

 30. And of the 16 dimes, divided accord- 

 ing to the year they were coined, how 

 many do you count in each pile? 



Another important fact to understand 

 about every classification is this: the 

 specimens in the first subdivision have 

 few characteristics in common. For ex- 

 ample, the 60 United States coins form 

 a group of considerable variety; they 

 arc alike in two respects only, they are 

 metal coins and thev^ are United States 

 coins. But specimens in the final sub- 

 division have many characteristics in 

 common. For example, the three pennies 

 in the final subdivision are alike in beinir 

 metal coins, of the United States, being 

 made of "copper," having the same size, 

 the same color, the same value, and lastly 

 being of the same age. It should not sur- 

 prise you that this group contains fewer 

 specimens. Thev mu.st be matched in 



many details before they can be fitted 

 into this group. 



The classification of plants and animals. 

 It is relatively easy to classify stamps and 

 coins. But plants and animals are so much 

 more complex that their classification is 

 much more difficult. More than two 

 thousand years ago the great Greek 

 scientist and philosopher, Aristotle, wrote 

 detailed and accurate descriptions of 

 many animals. In doing this he came to 

 recoonize that certain ones had similar 

 characteristics. For example, he put rep- 

 tiles, birds, and fishes together into one 

 group, the egg-layers. You will remem- 

 ber from Problem i that we no longer 

 classify or group together animals on 

 the basis of laying eggs. We use other 

 characteristics. 



As biologists continued their studies 

 they found that they were continually 

 obliged to change the classification be- 

 cause new facts were discovered about 

 the animals and plants then known, and 

 new plants and animals were being dis- 

 covered. The simple systems of classifi- 

 cation originally used were no longer 

 satisfactory. As a matter of fact, changes 



