MEANING OF ORDERS. ro 
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 trachee, 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- 
4* , FE 
