ANIMALS, MINERALS, AND PLANTS 9 



definition which will include all animals and exclude all 

 plants, and vice versa. If it is said that animals move, we 

 may reply that many plants, especially certain aquatic 

 plants, move as freely as animals. If it is said that animals 

 have sensibility, we may reply that plants show the same 

 characteristic. If it is said that plants have a green color- 

 ing matter, chlorophyll, we may point to the same sub- 

 stance foimd in the bodies of certain fresh-water hydras. 

 If it be maintained that animals take up oxygen and give 

 off carbon dioxide, we can demonstrate that plants do pre- 

 cisely the same thing. There is, however, one character- 

 istic common to aU plants and all animals ; namely, the 

 possession of life. 



Whether we deal with plants or animals, then, we shall l^e 

 in constant contact with life and yet probably never be 

 able to tell exactly what it is. We can, nevertheless, find 

 out something of the attributes and characteristics of life, 

 and that will be our aim in the following pages. 



Zoology. — By separating the term zoologi/ into its 

 parts, we find it is made up of two Greek words; namely, 

 zoon — animal, and logos — discourse. Therefore, Zool- 

 ogy may very properly be termed a discourse on the habits, 

 structures, development, and functions of animals. 



Zoology, along with chemistry and physics, is one of the 

 most extensive of all the sciences. The species of animals 

 upon the earth are myriad in number. It is estimated 

 that there are over a million species of insects alone, of 

 which over three himdred thousand have actually been 

 studied and named. 



Among so vast a number of animals, many forms are met 

 that are apparently unlike in every way. Yet each animal 

 wliich we shall study or which we may find upon the earth 



