THE MICROSCOPE AND ITS REVELATIONS. 



tute a large part of its aliment, this speedily dies, even though, instead 

 of being swallowed, it escapes from their grasp; whilst, on the other 

 hand, minute Entomostraca, Insects, and other animals with hard enve- 

 lopes, may escape without injury, even after having been detained for 

 some time in the polype's embrace. The contractility of the tentacles 

 (the interior of which is traversed by a canal that communicates with 

 the cavity of the stomach) is very remarkable, especially in the Hydra 

 fusca whose arms, when extended in search of prey, are not less than 

 seven or eight inches in length; whilst they are sometimes so contracted, 

 when the stomach is filled with food, as to appear only like little tubercles 



FIG. 354. 



Fio. 855. 



Hydra fusca, with a young bud at Hydra fusca in gemmation ; a, mouth ; 6, 



6, and a more advanced bud at c. base ; c, origin of one of the buds. 



around its entrance. By means of these instruments the Hydra is 

 enabled to draw its support from animals whose activity, as compared 

 with its own slight powers of locomotion, might have been supposed to 

 remove them altogether from its reach; for when, in its movements 

 through the water, a minute Worm or a Water-flea happens to touch one 

 of the tentacles of the Polype, spread-out as these are in readiness for 

 prey, it is immediately seized by this, other arms are soon coiled around 

 it, and the unfortunate victim is speedily conveyed to the stomach, 

 within which it may frequently be seen to continue moving for some 

 little time. Soon, however, its struggles cease, and its outline is 



