48 CLASSIFICATION AND CREATION. | 
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The internal cavity and the radiating tubes, ld. ee 
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 cemcmem; www w, interambulacra. 
quite distinct from the wall of the body. But 
notwithstanding this difference, a transverse sec- 
