198 THE MICROSCOPE. 



destroyed by Hercules in the lake of Lerna, as we are informed in 

 fabulous history. 



Leeuwenhoeck, in 1703, was the first to draw attention to the 

 Hydra; and in 1739, M. Trembley, from the Hague, most accurately 

 described the habits of the animal. 



The extraordinary attenuation of the arms, until they can with 

 difficulty be detected, renders it surprising that they possess strength 

 sufficient to cope with the struggles of large worms and insects, round 

 which the hydra wraps them ; but, as the victim seems powerless when 

 once in the fatal coil, it has been thought they possess some electric 

 power similar to the eel and torpedo, that stun or destroy their prey 

 by electrical force; and this belief is more especially entertained, as the 

 little creature rests, like the above-named fish, before regaining power 

 to resume its pursuit of prey. 



Polyps are not vegetarians, and were fed by M. Trembley on 

 minced fish, beef, mutton, and veal; they are voracious and active in 

 seizing worms and larvse much larger than themselves, which they 

 devour with avidity. They carefully and adroitly bring their food 

 towards their mouth ; and when near, pounce upon it with eagerness. 

 To make up for the want of teeth, the mouth enlarges to receive the 

 food brought to it by the arms that have twined round the sacrifice. 

 The red worm that tinges the mud of the Thames appears to be the 

 dainty dish they like best to have set before them. Dr. Mantell saw 

 the lasso of a polyp thrown over two worms at the same time ; yet they 

 could not escape, and lost all power of motion. 



Dr. Johnston writes : " Sometimes it happens that two polyps will 

 seize upon the same worm, when a struggle for the prey ensues, in 

 which the strongest gains, of course, the victory ; or each polyp begins 

 quietly to swallow his portion, and continues to gulp down his half, 

 until the mouths of the pair near, and come at length into actual con- 

 tact. The rest that now ensues, appears to prove that they are sensible 

 of their untoward position, from which they are frequently liberated 

 by the opportune break of the worm, when each obtains his share ; 

 but should the prey prove too tough, woe to the unready ! the more 

 resolute dilates the mouth to the requisite extent, and deliberately 

 swallows his opponent ; sometimes partially, so as, however, to compel 

 the discharge of the bait; while at other times the entire polyp is 

 engulfed ! But a polyp is no fitting food for a polyp, and his capacity 

 of endurance saves him from this living tomb ; for, after a time, when 

 the worm is sucked out of him, the sufferer is disgorged with no other 

 loss than his dinner." 



