150 ANIMALS AND PLANTS. [LECT. 



wards moisture, and their leaves towards air and 

 light, 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, deduces the necessity of the 

 existence in them of an alimentary 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 distinction 

 between animals and plants. 



Following out his teleological argument, Cuvier 

 remarks that the organisation of this cavity and its 

 appurtenances 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 im- 

 portant 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 



