MANUAL OF NATURAL HISTORY. 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. ORDER. 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. Horned-Hydatids (Ditrachyceratidee). 



Body ovate, compressed ; anterior extremity 

 furnished with two long horns and filaments. 



ACRITE-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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