NUTRITION IN POLYTI. 59 



account of his observations. The liydra, though it does not 

 pursue the animals on which it feeds, yet devours with avi- 

 dity all kinds of living prey that come witliin the reach 

 of its tentacula, and which it can overcome and introduce 

 into its mouth. The larvai of insects, naides, and other 

 aquatic worms, minute Crustacea, and even small fishes, arc 

 indiscriminately laid hold of, if they happen ])ut to touch 

 any part of the long filaments which the animal spreads out, 

 in different directions, like a net in search of food. The 

 struggles of the captive which finds itself entangled in the 

 folds of these tentacula, are generally ineffectual, and the hy- 

 dra, like the boa constrictor, contrives, by enormously ex- 

 panding its mouth, slowly to draw into its cavity animals 

 much larger than its own body. Worms longer than itself 

 are easily swallowed by being previously doubled together 

 by the tentacula. Fig. 242 shows a hydra in the act of de- 

 vouring the vermiform larva of a Tijjula, which it has en- 



circled with its tentacula, to which it has applied its expand- 

 ed mouth, and of which it is absorbing the juice, before 

 swallowing it. Fig. 243 shows the same animal, after it has 

 succeeded, though not without a severe contest, in swallow- 

 ing a minnow, or other small fish, the form of which is still 

 visible through the transparent sides of the body, which are 

 stretched to the utmost. It occasionally happens, when 

 two of these animals have both seized the same object by 



