444 CLASSIFICATION OF RADIATA. 



walls, opening from an intestinal tube which connects them all. 

 Much doubt yet exists on this subject, however ; and until their 

 real structure has been more fully determined, their place in the 

 Animal kingdom cannot be satisfactorily assigned. No traces of 

 a nervous system can be discovered even in the most highly- 

 organised among them, by which this question could be set at 

 rest. "We shall associate them with the Radiated classes, on 

 account of the general simplicity of their structure. 



