ANIMALS AND PLANTS. 157 



although the parts of some plants exhibit oscillating 

 movements without any perceptible cause, and the leaves 

 of others retract when touched, yet none of these 

 movements justify the ascription to plants of perception 

 or of will. From the mobility of animals, Cuvier, with 

 his characteristic partiality for teleological reasoning, de- 

 duces the necessity of the existence in them of an aliment- 

 ary cavity, or reservoir of food, whence their nutrition 

 may be drawn by the vessels, which are a sort of internal 

 roots ; and, in the presence of this alimentary cavity, he 

 naturally sees the primary and the most important dis- 

 tinction between animals and plants. 



Following out his teleological argument, Cuvier re- 

 marks that the organisation of this cavity and its appur- 

 tenances must needs vary according to the nature of the 

 aliment, and the operations which it has to undergo, 

 before it can be converted into substances fitted for 

 absorption ; while the atmosphere and the earth supply 

 plants with juices ready prepared, and which can be 

 absorbed immediately. As the animal body required 

 to be independent of heat and of the atmosphere, there 

 were no means by which the motion of its fluids could 

 be produced by internal causes. Hence arose the second 

 great distinctive character of animals, or the circulatory 

 system, which is less important than the digestive, since 

 it was unnecessary, and therefore is absent, in the more 

 simple animals. 



Animals further needed muscles for locomotion and 

 nerves for sensibility. Hence, says Cuvier, it was neces- 



