CHAPTER III 

 ORGANIC EVOLUTION 



It is a matter of common observation that the character- 

 istics of plants and animals are plastic, and more or less 

 responsive to conditions about them. We all know this to 

 be true of individuals. One familiar with the breeding of 

 plants and animals knows it is also true of species. How 

 great the changes, that may be wrought in a compara- 

 tively short time is shown by every cultivated species of 

 plant or animal. That comparable changes are wrought in 

 nature, only less rapidly, and that the main trend of the 

 change has been toward higher organization, has long been 

 thought, and is now generally believed. This is evolution. 

 It means "descent with modification." Forms now existing 

 differ from their remote progenitors. The complex struc- 

 tures and relations of the present day have developed out of 

 the simpler ones that have existed in the past, and the his- 

 tory of that development is a proper subject for investiga- 

 tion, being traceable in the constitution of the living, and in 

 the remains of extinct forms of life. 



In this chapter, in taking up for brief consideration the 

 higher plants and animals, we shall study them in series, 

 beginning with the simpler among them. This is the logical 

 order, the order which we follow in all our studies. It is 

 also the genetic order, the order of departure from primitive 

 conditions, the order of the appearance of the respective 

 groups upon the earth. We shall see the nature of the evi- 

 dence of their kinship, while seeing the nature of the plants 

 and animals about which we wish to learn. 



