MANUAL OF NATURAL HISTORY. 337 



and swim through the water with tolerable velocity, 

 propelled by the^ alternate contractions of the bell- 

 shaped halves of their bodies. 



The Sea-Nettles are predaceous in their habits, 

 and, notwithstanding the extremely delicate nature 

 of their organization, are enabled frequently to seize 

 and devour animals of much greater power by means 

 of their long stinging tentacles, which enlace their 

 victims, and at the same time benumb them. 



II. CLASS.— SEA-NETTLES (Acalephae). 



Animals soft, aquatic, free, gelatinous, emitting an 

 acrid secretion ; mouth and anus distinct. Swim by 

 contractions of the mantle, or by air-bladders. 



I. ORDER — Physograde Sea-Nettles (Physogradse). 



Body symmetrical, bilateral, fleshy, contractile, 

 provided with an aeriferous sac. 



1. Family. — Portuguese Men-of-war (Physaliidae). 



Vesicle large, irregular, without stalk or am- 

 pullae ; with terminal suckers and cirrhi. 



2. Family. — Bubble-bearers (Physophoridae). Vesicle 



small, regular, on a stalk, with lateral am- 

 pullae and terminal suckers. 



3. Family. — Scale-bearers (Rhodophysidae). Loco- 



motive organs in the form of smooth scales, 

 disposed in transverse series. 



II. ORDER PULMONIGRADE SEA-NETTLES 



(Pulmonigradse). 

 Body entirely gelatinous, circular, without any 



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