Hydra 45 



ten days, and then a particle of raw meat is 

 placed near one of its tentacles, it at once 

 fastens itself on the meat, and then the other 

 tentacles close round the food and contract; 

 in this way the particle is conveyed to the 

 Hydra's mouth, which opens to receive it, and 

 closes again as the food passes into the body 

 cavity where it is digested. If a particle of 

 meat is dropped by a Hydra when being con- 

 veyed to its mouth, the animal does not appear 

 to make any effort to recover it, although its 

 tentacles may continue to move about in an 

 excited manner for some little time. If a piece 

 of filter-paper is placed near a starving Hydra, 

 the animal does not attempt to seize it. "A 

 mechanical stimulus alone, then, cannot call 

 forth a food reaction." 1 In addition to the 

 mechanical stimulus to produce such a reaction, 

 the object must possess chemical properties of 

 a definite kind. For instance, a Hydra will 

 seize and swallow a morsel of filter-paper which 

 has been soaked in beef-tea. 



From the above facts we learn that Hydra 



1 The Quarterly Journal of Miscroscoftic Science, Now Series, 

 No. 192. 



