EXISTING ORGANISMS— CLASSIFICATION 



29 



Relationships. Protoplasm. A complete dissertation on the 

 relationship of minor groups of animals would involve more details 

 than could be set down in a single volume, but many [)oints of 

 fundamental relationship are visible in organisms whicii can 

 readily be appreciated in a brief outline. Broadest in scope is the 

 common basis of all life, plant and animal, the substance proto- 

 plasm. Protoplasm is 

 made up of three chem- ^=>s.^ vs"^" 

 ical compounds, pro- 

 teins, carbohydrates 

 and fats, associated 

 with various inorganic 

 compounds such as 

 water and common salt, 

 which are not changed 

 by the bod3\ The fats 

 and carbohydrates are 

 made up of the ele- 

 ments carbon, hydro- 

 gen and oxygen, while 

 proteins include these 

 three together with ni- 

 trogen, sulphur and in 

 some cases phosphorus Aesozoa' 



and iron. The proper- Infi^jonajis 

 ties of protoplasm are 

 the same in all organ- 

 isms. In addition to 

 its definitive chemical 

 composition, it is en- 

 abled to continue its 

 existence and activity, 

 and to grow and reproduce, by taking in other substances, chang- 

 ing them chemically through the process of digestion and incorpo- 

 rating them into itself. This process is called intussusception. 

 After the substances have become an integral part of the body, 

 their potential (nicn-gy is liberated by oxidation and thus activates 

 the organism. The waste products of oxidation are then passed 

 out of the body l)y the excretory system. The constructive part 

 of the entire interchange between the organism and its environ- 



FiG. 11. — Diagram, the tree of life. (From Out- 

 lines of Zoology, by J. Arthur Thomson, with 

 the permission of D. Appleton & Company.) 



