262 HIGH SCHOOL ZOOLOGY. 



state briefly the general principles which have been arrived at 

 bv zoolosrists in refjard to them, and to indicate the relations to 

 each other of the various aspects of zoological study. 



3. Zoology is one of the two divisions of biology (that 

 science which has for its subject-matter all things which have 

 or have had " life," in contrast to the lifeless objects of inor- 

 ganic nature), it is, in fact, the Biology of animals, while Botany 

 is the Biology of plants. It may be asked why, in the face of 

 the palpable diilerences which exist between plants and ani- 

 mals, it should be necessary to have a common term for the 

 study of the phenomena manifested by both. The answer is, 

 that the phenomena manifested by living matter in both king- 

 doms present such a striking contrast to those manifested by 

 not-living matter, that the study of the difference between them 

 becomes a question of the first importance. It is not meant 

 that the matter wliich enters into the composition of an organ- 

 ism is different from that of which lifeless things are made, for 

 there is a constant exchange of matter between the living and 

 the lifeless world. An organism has been well compared to a 

 wave formed by an obstruction in a rapid, the shape of which 

 is approximately constant, but the particles composing which 

 are incessantly changing. So the living organism is constantly 

 faking into it matter from the inorganic world around it, and, 

 as constantly, parting with matter to its surroundings (as we 

 see in its relations, for example, to the gases of the surround- 

 ing atmosphere). Nor is it meant that matter in an organism 

 conducts itself in any exceptional way, for wherever it has been 

 possible to follow the transformations of matter and of energy 

 in the living plant or animal, it has been found that these take 

 place in harmony with laws which have been deduced from the 

 conduct of matter in the inorganic world. What then are these 

 manifestations of " life " and the properties common to plants 

 and animals, which induce us to regard Zoology and Botany as 

 parts of a more comprehensive science — Biology % 



