THE ORGANISM AND ITS ENVIRONMENT 369 



had taken place. Another investigator repeated his experiments a 

 century later. Trembley had been deceived. By inverting its upper 

 end into the central cavity the hydra had found the bristle on which 



00 



4 s e 



Fig. 219. — Diagrams showing the righting behavior of a hydra that has been turned 



inside out. 



it was impaled, and then literally crept through the hole in its side. 

 The lower portion presently did the same thing in a similar way, 

 so that the animal was now righted, although still impaled on the 



