98 Cuvief'iaji System of Zoology. 



tions of animals make essential modifications necessary in those 

 organs, which may be regarded as simply vegetative. The 

 parts which perform the functions of roots do not penetrate 

 the ground, they are therefore obliged to have a power resid- 

 ing in themselves of gathering their aliments, and they must 

 also carry within themselves the receptacle of these aliments. 

 Hence arises the first character of animals, — an intestinal 

 cavity, whence the nourishing juices penetrate the other parts, 

 either by pores or by vessels, which may be regarded as 

 internal roots. The organisation of the intestinal cavity, and 

 of its appertenances, must naturally vary according to the 

 nature of the aliments, and the operations they must undergo, 

 before furnishing juices proper to be absorbed ; whereas the 

 atmosphere and the earth supply vegetables with juices already 

 prepared for absorption. The body of an animal, having to 

 perform functions more varied and numerous than those of a 

 plant, consequently required a much more complicated organ- 

 isation ; its parts, also, being unable to preserve a fixed position 

 in regard to each other, it was not possible for the regular 

 motion of its fluids to be affected by external causes. This 

 motion must be independent of temperature and the atmo- 

 sphere ; hence the necessity for the second character of animals, 

 a system of circulation : but this is less essential than the 

 digestive system, because it is not found in the most simple 

 animals. 



The functions of animals require organic systems that are 

 not necessary in vegetables, — a system of muscles for volun- 

 tary motion, and a system of nerves for sensation. The che- 

 mical composition of the animal body is also more complicated 

 than that of a plant, and there enters into it an additional 

 essential elementary substance, azote, which in plants is only 

 accidentally united with the three essential elements of their 

 organic structure, — oxygen, hydrogen, and carbon. The mus- 

 cular and nervous systems, and the different composition of ani- 

 mal bodies, form the third character. 



The soil and the atmosphere present to vegetables, for their 

 nutrition, water, which is composed of oxygen and hydrogen ; 

 and atmospheric air, which contains oxygen, azote, and carbonic 

 acid : the latter is a combination of carbon and oxygen. To 

 draw from these aliments their proper nourishment, it is neces- 

 sary that plants should retain the hydrogen and the carbon, 

 and that they should exhale the superfluous oxygen, and ab- 

 sorb little or none of the azote : such is the routine (la marche) 

 of vegetable life, the essential function of which is the exha- 

 lation of oxygen ; this is performed by the aid of light. The 



