INFUSORIA. 447 



CLASS XIV. INFUSORIA. 



Microscopic animals, gelatinous, transparent, polymorphous, 

 and contractile ; no distinct mouth, nor constant or deter- 

 minable interior organ ; generation fasiparous or gemmi- 

 parous. 



THE Infusory Animals, or those animalcules which have been 

 observed in infusions of different plants, or in waters more or 

 less corrupted, and which are generally so minute as to require 

 the aid of the microscope to discover them, form the last series 

 of beings in the animal scale. The greater portion of these ap- 

 pear to have a gelatinous body of extreme simplicity ; but sys- 

 tematical writers have also arranged in this class many animals 

 much more complicated in appearance, and which resemble them 

 only in their extreme minuteness. 



Of animals so minute, the organization is but imperfectly 

 known. Destitute of a distinct mouth and internal organ of di- 

 gestion, they seem to receive nourishment by absorption in all 

 parts of their body. They are, however, capable of contraction 

 and voluntary motion ; and their reproduction is effected by a 

 separation of parts. 



Lewenhoeck and Muller first introduced these animalcules to 

 the notice of naturalists under the name of Infusoria. In La- 

 marcFs system they compose the first class of his Invertebral 

 animals ; Dumeril arranges them as the fourth family of his 

 Zoophytes ; and Cuvier makes them the fifth class of Zoophy- 

 tes, or those animals which he has arranged as the fourth 

 great division of the Animal Kingdom. Lamarck divides the 

 Infusoria into two orders : 



I. INFUSORIA APPENDICULATA. With projecting parts at 

 their exterior, as hairs, horns, or a tail. 



II. INFUSORIA NUDA, or Naked Infusoria. Destitute of 

 exterior appendages. 



