So ZOOLOGY. 



2. Associations of tissues to accomplish a more or less defi- 

 nite work are called organs : organs of a similar kind are col- 

 lectively 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. 



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



(c) Growth 



(d) Reproduction . . Reproductive. 



(e) Motion Muscular, in connection with 



skeletal. 

 (/) Sensation Nervous. 



4. Metabolism or nutrition embraces the following proc- 

 esses : 



(a) Ingestion of food (including oxygen), 



(b) Digestion, 



(c) Absorption, 



(d) Circulation, 



(e) Assimilation = anabolism, 

 (/) Dissimilation = katabolism, 



(g) Secretion and excretion (of waste matter including car- 

 bon dioxid). 



The processes in (a), (b), (c), and (e) are anabolic, i. e., 

 add to the resources of the body. Those in (/) and (g) are 

 katabolic, i. e., tend to destroy the materials, develop energy, 

 and eliminate waste. Circulation contributes to the accom- 

 plishment of both purposes. 



5. The supportive skeletal structures may be internal, or 

 external, or both. They may arise as a secretion of the super- 

 ficial cells of the body, or consist of a mixture of cells and 

 intercellular substance. Their nature and arrangement are 

 profoundly important in determining the distribution of the 

 other more active organs. 



6. Growth and reproduction are the outcome of the nutri- 



