INTRODUCTORY : THE ANIMAL ORGANISM 21 



Physiology, which deals with their functions. In the follow- 

 ing pages we shall regard Zoology in the first place from the 

 anatomical point of view, but shall seek from Physiology 

 light upon the meaning of the structures described, endea- 

 vouring to trace in the bodies of the animals studied the 

 provision which exists for carrying out all those functions 

 which our first survey has revealed to us as taking place. 



..&•*■ 



A B C 



Fig. 5. — Portions of tissues, highly magnified, to show cells. 



A , The lining of an artery ; B, muscular tissue from the wall of the intestine ; 



C, the lining of the intestine. A and B are shown in surface view, C 



in section. 

 c, Cells ; g.s. t ground or intercellular substance, traversed by threads of 



protoplasm from cell to cell. 



With this purpose we shall examine in considerable detail 

 first one of the higher animals and then an exceedingly 

 simple example, tracing afterwards, in a series of further 

 examples, the gradual increase in organisation and the 

 varieties that it presents. Finally we shall take opportunity 

 to discuss more fully various aspects and processes of life in 

 the light of further knowledge. 



