TREMBLEY*S UYDRA. 179 



Hydras are lound in grassy waters, lakes, pools, 

 and canals. The best mean cf procuring them is 

 to take haphazard, from the water supposed to 

 contain them, any aquatic plants, leaves of trees 

 that have fallen into the water, or bits of wood 

 which have accumulated there, and to these the 

 hydras will be found attached. They transport 

 themselves from one point to another by swimming 

 or crawling. 



Trembley has made a special study of three species 

 of hydra. He has named them the long-armed poly- 

 pus, green polypus^ and hroivn or grey polypus (Hydra 

 Grisea). Their bodies, which are very contractile, 

 are variously formed. The tentaculaj are often 

 immoveable. The ordinary species, including their 

 arms, may reach five-eightlis of an inch in length, 

 but other species attain larger dimensions. 



Ancient writers mention, under the name of hydra, 

 a mythologic animal with seven heads, each of whicli 

 was reproduced as fast as it was cut off. Trembley 's 

 hydra, more accomplished than tbis fabulous animal, 

 formed two perfect creatures when divided. Nor 

 is this all. What does the reader, when made 

 acquainted with the fact for the first time, think of 

 an animal able to turn itself inside-out like a glove 

 without ceasing to live ? Trembley tells us that his 

 hydra undergoes this operation without being in the 



