ORGANIZATION. 



41 



FIG. 14. A Ganglion of the Sympathetic Nerve of a Mouse. 



3. Organs, and their Functions. Animals, like Plants, 

 grow, feel, and move ; these three are the capital facts of 

 every organism. Besides these there may be some pecul- 

 iar phenomena, as motion and will. 



Life is manifested in certain special operations, called 

 functions, performed by certain special parts, called or- 

 gans. Thus, the stomach is an organ, whose function is 

 digestion. A single organ may manifest vitality, but it 

 does not (save in the very lowest forms) show forth the 

 whole life of the animal. For, in being set apart for a 

 special purpose, an organ takes upon itself, so to speak, to 

 do something for the benefit of the whole animal, in return 

 for which it is absolved from doing many things. The 

 stomach is not called upon to circulate or purify the blood. 



There may be functions without special organs, as the 

 Amoeba digests, respires, moves, and reproduces by its 

 general mass. But, as we ascend the scale of animal life, 

 we pass from the simple to the complex : groups of cells 

 or tissues, instead of being repetitions of each other, take 

 on a difference, and become distinguished as special parts 

 with specific duties. The higher the rank of the animal, 

 the more complicated the organs. The more complicated 

 the structure, the more complicated the functions. But in 



