NUTRITION IN POLYri. 61 



allowing of its progress being traced into the granules which 

 are dispersed throughout the substance of the body. Trem- 

 bley is of opinion that these granules are vesicular, and that 

 they assume the colour they are observed to have, from 

 their becoming filled with the coloured particles contained 

 in the nourishment. The granules which are nearest to the 

 cavity of the stomach are those which are first tinged, and 

 which therefore first imbibe the nutritious juices: the others 

 are coloured successively, in an order determined by their 

 distance from the surface of the stomach. Trembley ascer- 

 tained that a living hydra introduced into the stomach of 

 another hydra, was not in any degree acted upon by the 

 fluid secretions of that organ, but came out uninjured. It 

 often happens that a hydra, in its eagerness to transfer its 

 victim into its stomach, swallows several of its own tenta- 

 cula, which had encircled it: but these tentacula always ul- 

 timately came out of the stomach, sometimes after having 

 remained there twenty-four hours, without the least detri- 

 ment. 



The researches of Trembley have brought to light the 

 extraordinary fact that not only the internal surface of the 

 stomach of the polypus is endow^ed with the power of di- 

 gesting food, but that th^ same property belongs also to the 

 external surface, or wiiat we might call the skin of the ani- 

 mal. He found that b}^ a dexterous manipulation, the hy- 

 dra 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 accommo- 

 dates itself in the course of a day or two to the transforma- 

 tion, and resumes all its natural habits, eagerly seizing ani- 

 malcules with its tentacula, and introducing them into its 

 newly formed stomach, which has for its interior surface 

 what before was the exterior skin, aaul which digests them 

 with perfect ease. When the discovery of this curious phe- 

 nomenon was first made known to the world, it excited 

 great astonishment, and many naturalists were incredulous 



