53o DESCRIPTION OF THE MUSEUM. 



grafted together by the lower extremity, and 

 partake of the same nutriment, they may he said 

 to constitute but one complex animal. 



Although the polypi are the most simple in 

 their organization of all living beings, their vital 

 phenomena, when first described by Trembley, 

 excited to the highest degree the interest and 

 astonishment of naturalists. We shall here men- 

 tion some of the observations made on the naked 

 or soft polypi, and more particularly on a spe- 

 cies of the genus hydra, which is common in our 

 stagnant waters. The hydrce propagate them- 

 selves by means of gemmce. A small bud grows 

 on the tube, lengthens and becomes a new animal, 

 which either remains fixed on the first, or falls off, 

 and in turn becomes the parent stalk on which 

 new individuals branch in the same manner. They 

 also multiply by being severed, and however 

 small the parts into which an hydra is cut, they 

 soon become complete animals. The hydra vi- 

 ridis, the form of which is that of a bag, can be 

 turned inside out without the least inconve- 

 nience to the life or habits of the animal, the 

 exterior surface, now become the interior, per- 

 forming the function of digestion, 



The second order of the polypi is composed 

 of those which have a calcareous or horny enve- 

 lope, the result of an exudation from their body, 



