CHAPTER III 



THE STRUCTURE AND FUNCTIONS OF THE 

 ANIMAL BODY 



Organs and functions. The body of the toad is com- 

 posed of various parts, such as the lungs, the heart, the 

 muscles, the eyes, the stomach, and others. The life of 

 the toad consists of the performance by it of various 

 processes, such as breathing, digesting food, circulating 

 blood, moving, seeing, and others. These various 

 processes are performed by the various parts of the body. 

 The parts of the body are called organs, and the processes 

 (or work) they perform are called their functions. The 

 lungs are the principal organs for the function of breath- 

 ing; the heart, arteries and veins are the organs which 

 have for their function the circulation of the blood ; the 

 principal organ concerned in the digestion of food is the 

 alimentary canal, the function of seeing is performed by 

 the organs of sight, the eyes, and so one might continue 

 the catalogue of all the organs of the body and of all the 

 functions performed by the animal. 



The animal body a machine. The whole body of the 

 toad is a machine composed of various parts, each part 

 with its special work or business to do, but all depending 

 on cne another and all co-operating to accomplish the total 

 work of living. The locomotive engine is a machine 

 similarly composed of various parts, each part with its 

 special work or function, and all the parts depending on 

 one another and so working together as to perform satis- 



14 



