TURBELLAEIA. 13 



structure, genesis, and development of this diversely organized 

 group; yet, on the other hand, sufficient appears to have been 

 recorded in order to show that we are hardly warranted in sepa- 

 rating these creatures from the sterelminthic entozoa, properly so 

 called. Those who, with Von Siebold, prefer to retain the Tur- 

 bellarians as a separate class, and who, at the same time, thrust 

 the Nemertian division into the annelids proper, should, I conceive, 

 in all fairness, not stop here, but cut away the Trematoda also, and 

 make them an aberrant annelidan group by linking them and the 

 Planarians on to the Annehda through the intervention of the 

 closely allied Suctoria. At all events, with an equal show of 

 reason, we might associate the Nematoda with the earthworms and 

 other scolecine annelids; but I think it is now sufficiently well 

 understood that any splitting of the Entozoa proper would only be 

 attended with numerous disadvantages, not counterbalanced by 

 those compensating features which ordinarily justify any radical 

 change. 



