MANUAL OF NATUBAL HISTOBY. 363 



7. Family. — Polystome - Flukes (Polystomatidse). 

 Mouth with six, bilocular, biperforate suckers, 

 placed beneath anterior extremity; body 

 elongated, depressed, not segmented, con- 

 stricted anteriorly, ending in a point behind. 



IV. OEDEE.— Vesicular-Worms (Cystica). 



Body cystiform, filled with fluid ; mouth furnished 

 with suckers, hooks, or filaments. 



1. Family. — Hydatids (Hydatidse). Body round 



or oblong ; mouth with four suckers, armed 

 with a hooked crown. 



2. Family. — Homed-Hydatids (Ditrachyceratidse). 



Body ovate, compressed ; anterior extremity 

 furnished with two long horns and filaments. 



ACEITE-ANIMALS. 



The Sub-kingdom of Radiata of Cuvier, which 

 nearly corresponds with the Polyps of Linnaeus, 

 has, from its vast extent, been of late years again 

 sub-divided. It therefore now comprehends the 

 Radiata or Nematoneura of Owen, which include 

 all the higher forms, or those in which a nervous 

 system can be distinctly traced, — and the Acrita, 

 first separated by Macleay, comprising the lowest 

 and most simple forms of animal existence. The 

 characters of Acrite animals being principally nega- 

 tive, nervous matter not having been hitherto 

 detected in their organization, it follows that its 



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