INTRODUCTION 



MANY problems, for some of which no answer has as 

 yet been found, arise in connection with the world of 

 living things. How did they arise ? How are they 

 scattered over the face of the earth ? What are they 

 in themselves and in all their parts ? How do they 

 feed and grow and reproduce their kind ? Why do 

 they grow old and die ? What is the secret of their 

 activity and of its ability to change with the changes 

 that occur in its surroundings ? 



These and many allied questions arise, and out of the 

 attempts to answer such questions has arisen Biology 

 or the Science of Life. 



Biology may be defined, in the words of Professor 

 J. Arthur Thomson, as " the science of the structure 

 and activity, development and evolution of organisms, 

 including man." 



It cannot be pointed out too early that Biology does 

 not concern itself with the particular kinds of plants 

 and animals ; that is the aim of the special sciences of 

 Botany and Zoology, but it has to answer questions 

 dealing with the form and structure of living things, 

 with their activities, their origin, and the factors in 

 their evolution. 



The first of these questions form and structure so 



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