48 CLASSIFICATION AND CREATION. 
The internal cavity and the radiating tubes, in- 
stead of being connected with the outer wall of 
Common Sea-Urchin, Echinus, seen from above. 
the body as in Polyps, or hollowed out of the 
substance of the body as in Jelly-Fishes, are here 
enclosed within independent walls of their own, 
Echinarachnius, opened by a transverse or horizontal section, and showing 
the internal arrangement: 0, mouth ; ee eee, ambulacra, with their rami- 
fications cme mem; www w, interambulacra. 
quite distinct from the wall of the body. But 
notwithstanding this difference, a transverse sec- 
