A MANUAL OF 

 ELEMENTARY ZOOLOGY 



CHAPTER I 



INTRODUCTORY: THE ANIMAL ORGANISM 



Nothing is of more importance to the student of Zoology 

 than to realise at the outset of his studies what 

 ujjoc. j s t j ie SCQ p e Q f ^jg sc ; ence> Zoology is con- 

 cerned with animals. Now it is quite possible to regard 

 animals merely as objects of certain shapes and sizes and 

 colours, and to study and classify them with reference to 

 these properties alone. But this procedure is both unin- 

 telligent and unfruitful. It ignores the meaning of the 

 facts which it collects, and leaves unanswered the questions 

 which they suggest. Properly to study any animal we 

 must inquire why its structure is what we find it to be, 

 and how it has come into being. That is to say, we must 

 study, with the structure of the body, the life which that 

 structure subserves and to which it owes its existence, for 

 the life of an animal not only requires in it a certain 

 structure, but is also the means by which that structure is 

 reached both in the individual and in the race. 



The life of an animal consists in a series of processes 



which take place in its body. So long as these 



processes go on the animal is said to be alive; 



when the body has lost the capacity for supporting them it 



is dead. In their main outlines the processes of life are 



familiar to every one, in his own person and in those of the 



men and animals about him. They may be stated as follows. 



I 



