MEANING OF ORDERS. 81 



with man at their head, include all these sys- 

 tems. 



According to Oken, the Radiates, the lowest 

 type of the Animal Kingdom, embody digestion. 

 They all represent a stomach, whether it is the 

 simple sac of the Polyps, or the cavity of the 

 Acalephs, with its radiating tubes traversing the 

 gelatinous mass of the body, or the cavity and 

 tubes of the Echinoderms, enclosed within walls 

 of their own. 



The Mollusks represent circulation ; and his 

 division of this type into classes, according to 

 what he considers the higher or lower organ- 

 ization of the heart, agrees with the ordinary 

 division into Acephala, Gasteropoda, and Cepha- 

 lopoda. 



The Articulates are the respiratory animals in 

 this classification : they represent respiration. 

 The Worms, breathing, as he asserts, through the 

 whole surface of the skin, without special breath- 

 ing organs, are the lowest ; the Crustacea, with 

 gills, or aquatic breathing organs, come next; 

 and he places the Insects highest, with their 

 branching tracheae, admitting air to all parts of 

 the body. 



The Vertebrates, or Flesh Animals, with their 

 four classes, represent the Bones, the Muscles, 

 the Nerves, and the Organs of Sense, the Fishes 

 being par excellence the bony animals, the Rep- 



