NUTRITION IN POLYPI. 79 



The researches of Trembley have brought to 

 Ught the extraordinary fact that not only the 

 internal surface of the stomach of the polypus is 

 endowed with the power of digesting food, but 

 that the same property belongs also to the ex- 

 ternal surface, or what we might call the skin of 

 the animal. He found that by a dexterous ma- 

 nipulation, the hydra may be completely turned 

 inside out, like the finger of a glove ; and that 

 the animal, after having undergone this singular 

 operation, will very soon resume all its ordinary 

 functions, just as if nothing had happened. It 

 accommodates itself in the course of a day or 

 two to the transformation, and resumes all its 

 natural habits, eagerly seizing animalcules with 

 its tentacula, and introducing them into its Dewly 

 formed stomach, which has for its interior sur- 

 face what before was the exterior skin, and 

 which digests them with perfect ease. When the 

 discovery of this curious phenomenon was first 

 made known to the world, it excited great asto- 

 nishment, and many naturalists were incredulous 

 as to the correctness of the observations. But 

 the researches of Bonnet and of Spallanzani, 

 who repeated the experiments of Trembley, 

 have borne ample testimony to their accuracy, 

 which those of every subsequent observer have 

 farther contributed to confirm. 



The experiments of Trembley have also proved 

 that every portion of the hydra possesses a won- 



