88 ZOOLOGY 



stimulate we must be able to do the right thing. This harmony 

 of operation among the parts is coordination. Harmony be- 

 tween the action of the organism and the outside conditions is 

 adaptation. The nervous system reintegrates these numerous 

 diverse units of which we are made, and makes them work 

 together. All the active cells of the body are connected by 

 way of the nervous elements. A part of the work of the hor- 

 mones is also of this higher coordinating value. It has been 

 found by experiment that the pancreas, for example, is brought 

 to secrete at the proper time by substances in the blood absorbed 

 from the digestive tract rather than through nervous action 

 purely, as we formerly thought. The hormones and the nerv- 

 ous system thus work together for active integration; but in 

 general the nervous system operates more immediately than 

 the chemical system. 



115. Summary. 



1. Division of labor and differentiation of structure proceed 

 together as the individual develops. All tissues retain the 

 power of using food, of oxidation, of eliminating useless prod- 

 ucts. Other functions incidental to these may be relegated to 

 special cells or tissues. 



2. Associations of tissues to accomplish a more or less definite 

 work are called organs. Organs of a similar kind are collectively 

 known as systems of organs. 



3. The principal functions of animals and the organs or 

 systems performing the work may be classed as follows : 



Function System 



(a) Metabolism Nutritive. 



(b) Support and protection. . . Skeletal, and integumentary. 



(c) Growth 



(d) Reproduction Reproductive. 



(e) Motion Muscular, in connection with 



skeletal. 

 (J) Sensation Nervous, including sensory epi- 

 thelium. 



4. Metabolism or nutrition embraces the following processes: 

 (o) Ingestion of food (including oxygen), 



