INTRODUCTION 
the road. Certain principles apply to things having life 
that make them different from things which do not have 
life. We may illustrate by saying that the one grows and 
changes while the other does not. We can establish group 
principles that apply to all individuals of the one sort or 
the other. 
Those things that are alive again divide themselves 
and make it possible for one to study smaller groups and 
learn principles that apply to them. In the living world 
there is the animal kingdom, which is made up of indi¬ 
viduals that can move about as can a jack rabbit, and the 
vegetable kingdom, into which are placed those that stay 
all the time in the same place as does a barberry bush. 
The members of one group, we may observe, have the 
power of choosing for themselves what they will do, while 
the members of the other group must get along wherever 
chance happens to place them. 
Not to follow these steps in classification too closely, we 
come, finally, perhaps, to an examination of certain fami¬ 
lies in the animal world. There is the sparrow family 
of birds, for example. Everybody knows the English 
sparrow. The song sparrow and the field sparrow are 
enough like it to be put at once into the same family. 
One might not think of the canary as a sparrow until he 
began to study its structural make-up and its habits, but 
if he should do so its family connection would be revealed. 
The snowbird of the winter is a sparrow. So is the purple 
finch and the curious crossbill that lives upon the seeds 
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