60 THE VITAL FUNCTIONS. 



its different ends, that a struggle between them ensues, and 

 that the strongest, having obtained the victory, swallows at 

 a single gulp, not only the object of contention, but its an- 

 tagonist also. The scene is represented in Fig. 244, where 

 the tail of the hydra, of which the body has been swallowed 

 by the victor, is seen protruding from the mouth of the lat- 

 ter. It soon, however, extricates itself from this situation, 

 apparently without having suffered the smallest injury. The 

 voracity of the hydra is very great, especially after long fast- 

 ing; and it will then devour a great number of insects, one af- 

 ter another at one meal, gorging itself till it can hold no more, 

 and its body becoming dilated to an extraordinary size: and 

 yet the same animal can continue to live for more than four 

 months without any visible supply of food. 



On attentively observing the changes induced upon the 

 food by the action of the stomach of these animals, they ap- 

 pear to consist of a gradual melting down of the softer parts, 

 which are resolved into a kind of jelly, leaving unaltered 

 only a few fragments of the harder and less digestible parts. 

 These changes are accompanied by a kind of undulation of 

 the contents of the stomach, backwards and forwards, 

 throughout the whole tube, apparently produced by the 

 contraction and dilatation of its different portions. The un- 

 digested materials being collected together and rejected by 

 the mouth, the remaining fluid is seen to contain opaque 

 globules of various sizes, some of which are observed to pe- 

 netrate through the sides of the stomach, and enter into the 

 granular structure which composes the flesh of the animal. 

 Some portion of this opaque fluid is distributed to the tenta- 

 cula, into the tubular cavities of \vhich it may be seen en- 

 tering by passages of communication with the stomach. By 

 watching attentively the motions of the globules, it will be 

 perceived that they pass backwards and forwards through 

 these passages, like ebbing and flowing tides. 



All these phenomena may be observed with greater dis- 

 tinctness when the food of the animal contains colouring 

 matter, capable of giving a tinge to the nutritious fluid, and 



