THE LIVING STRUCTURES 



149 



the swimming' animals and birds, and the long" neck of 

 the giraffe with which he reaches up to the high branches 

 of the trees on which he feeds are structures that arise 

 out of the desires and needs of the builders. Take for in- 

 stance hair, this is a covering mainly to keep the body at 

 an equal temperature. In a cold climate the covering 



FIG. 29. Bird descending. (Made by man.) 



must be provided either by the cells in the body or by the 

 acts of the individual himself, as in the case of man. The 

 cells of a man do not make hair on the body, after having 

 discovered a better way of covering the same with the 

 skins of animals or otherwise, which covering can be re- 

 moved when not required. Hair is produced as it is de- 

 sired and necessary. On the animals farthest south the 



