NUTRITION IN POLYPI. 77 



apparently without having suffered the smallest 

 injury. The voracity of the hydra is very great, 

 especially after long fasting ; and it will then 

 devour a great number of insects, one after ano- 

 ther, at one meal, gorging itself till it can hold 

 no more ; its body becoming dilated to an extra- 

 ordinary size ; and yet the same animal can 

 continue to live for more than four months with- 

 out any visible supply of food. 



On attentively observing the changes induced 

 upon the food by the action of the stomach of 

 these animals, they appear to consist of a gradual 

 melting down of the softer parts, which are re- 

 solved 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 I'emaining fluid is 

 seen to contain opaque globules of various sizes, 

 some of which are observed to penetrate through 

 the sides of the stomach, and enter into the gra- 

 nular structure which composes the flesh of the 

 animal. Some portion of this opaque fluid is 

 distributed to the tentacula ; into the tubular 

 cavities of which it may be seen entering by 

 passages of communication with the stomach. 



