114 SOXE WONDEKS OF THE SEA. 



like the long-armed fresh-water Polype, which has been 

 for so many years a favourite object of investigation. 



Although so small, the Hydra has the power of seizing 

 the little animals which swim through the water. If 

 they once come across a single tentacle of the Polype, 

 their fate is certain. Their course is suddenly arrested, 

 and- although the thread be invisible to our eyes without 

 the aid of a tolerably powerful magnifying-glass, the 

 victim seems to be instantaneously paralyzed, and even 

 if the first struggle on being seized should cause it to 

 shake itself loose for a moment, it invariably dies. 



It is worthy of remark that, in one of its many 

 changes, the common Medusa assumes so precisely the 

 form of the short-armed, fresh-water polype, that if the 

 two animals were drawn to the same scale, and the 

 portraits placed side by side, it would not be easy to say 

 which was the perfect polype of the river, and which was 

 the imperfect jelly fish of the sea. 



A new arrangement of the various organs now comes 

 before us : Fig. 2. 



In the Diphyes, the principal thread, to which the 

 pearl-like sacs and their pendent threads are attached, is 

 very long. In the animals belonging to the Physophores 

 it is quite short in proportion to the fishing-threads. 

 The swimming bells are increased in number, and in this 

 case there are six fully developed bells on each side. 

 Below them are the tentacles and their appendages, and 

 a torrent of fishing-threads hangs from them, looking like 

 an inverted plume of spun glass. In one species, called 



