160 ANIMALS AND PLANTS. 



his elaborate and comprehensive work on the Infusoria, 

 had declared the greater number of what are now rec- 

 ognised as locomotive plants to be animals. 



At the present day, innumerable plants and free 

 plant cells are known to pass the whole or part of their 

 lives in an actively locomotive condition, in no wise 

 distinguishable from that of one of the simpler animals ; 

 and, while in this condition, their movements are, to all 

 appearance, as spontaneous as much the product of 

 volition as those of such animals. 



Hence the teleological argument for Cuvier's first 

 diagnostic character the presence in animals of an ali- 

 mentary cavity, or internal pocket, in which they can 

 carry about their nutriment has broken down, so far, 

 at least, as his mode of stating it goes. And, with the 

 advance of microscopic anatomy, the universality of the 

 fact itself among animals has ceased to be predicable. 

 Many animals of even complex structure, which live 

 parasitically within others, are wholly devoid of an ali- 

 mentary cavity. Their food is provided for them, not 

 only ready cooked, but ready digested, and the alimentary 

 canal, become superfluous, has disappeared. Again, the 

 males of most Rotifers have no digestive apparatus ; as 

 a German naturalist has remarked, they devote them- 

 selves entirely to the " Minnedienst," and are to be reck- 

 oned among the few realisations of the Byronic ideal of 

 a lover. Finally, amidst the lowest forms of animal 

 life, the speck of gelatinous protoplasm, which consti- 

 tutes the whole body, has no permanent digestive cav- 



