326 ANIMALIA RADIATA. 
from Polypi in the greater development of the tissue of their 
organs. The Acalepha Hydrostatica, which we place at the 
end of this class, when better known, will perhaps form a 
separate one; as yet however we only conjecture the functions 
of their singular organs. 
The Potyrr, which compose the fourth class, are those 
little gelatinous animals whose mouth surrounded with tenta- 
cula leads to a stomach sometimes simple and sometimes fol- 
lowed by intestines in the form of vessels. To this class be- 
long those innumerable compound animals with a fixed and 
solid stem which were considered as marine plants. 
The Thethyiz and Sponges are usually placed at the end 
of this class, although Polypi have not yet been discovered in 
them. 
The Inrusonta, or the fifth and last class of the Zoophyta, 
are those minute beings whose existence we have only dis- 
covered by means of the microscope, and which swarm in 
stagnant waters. Most of them have merely a gelatinous 
body destitute of viscera, although we commence the series 
with more compound species possessed of visible organs of 
locomotion and a stomach: these also may hereafter consti- 
tute a separate class. 
