CHAPTER VII 



MULTICELLULAR ANIMALS: HYDRA FUSCA 

 GENERAL LIFE FUNCTIONS OF ANIMALS 



THE life of animals is much more complicated than that of 

 plants and the animal body is correspondingly more complex. 

 It will make the study of multicellular animals more intelligible 

 if at the outset we notice certain general functions of life that 

 are exhibited by all higher animals. They are as follows : 



Alimentation (Lat. alimentum = food). The process of 

 food getting is called alimentation. The organs concerned in 

 it are those that take food into the body, those that digest it, 

 and finally those that absorb it into the circulating medium. 



Circulation. The process by which food and other ingredients 

 are transported through the body is called circulation. Usually 

 it is brought about by a circulating medium called the blood, by 

 a series of tubes in which the blood is carried, known as blood 

 vessels, and by a pump, or heart, designed to keep the blood in 

 motion. In some of the smaller animals this system of organs 

 is far simpler, neither blood vessels nor a heart being present; 

 but some form of circulation is always found. 



Respiration. The chief chemical process in the animal body 

 is oxidation, i.e., the combination of the food with the oxygen. 

 For this purpose, oxygen gas must be absorbed by the blood. 

 As a result of the oxidation of the food another gas (CO 2 ) arises, 

 which is also taken up by the blood and must be eliminated, 

 since it is a waste product. The function by which these two 

 gases (O and CO 2 ) are absorbed and discharged is called respira- 

 tion. Respiration is thus a gas exchange that takes place be- 

 tween the body and the surrounding medium. 



Metabolism (Gr. meta = beyond + ballein = to throw). 

 The foods taken into the body are eventually combined with 

 the oxygen taken in by respiration and as a result new products 



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