NUTRITION IN POLYPI. 81 



means they quickly unite, and become a com- 

 pound animal. When the body of one hydra is 

 introduced into the mouth of another, so that 

 their heads are kept in contact for a sufficient 

 length of time, they unite and form but one in- 

 dividual. A number of heads and bodies may 

 thus be joined together artificially, so as to com- 

 pose living monsters more complicated than the 

 wildest fancy has conceived. 



Still more complicated are the forms and eco- 

 nomy of those many-headed monsters, which 

 prolific nature has spread in countless multitudes 

 over the rocky shores of the ocean in every part 

 of the globe. These aggregated polypi grow, in 

 imitation of plants, from a common stem, with 

 widely extended flowering branches. Myriads 

 of mouths open upon the surface of the animated 

 mass; each mouth being surrounded with one 

 or more circular rows of tentacula, which are 

 extended to catch their prey : but as the station- 

 ary condition of these polypes prevents them 

 from moving in search of food, their tentacula 

 are generally furnished with a multitude of cilia, 

 which, by their incessant vibrations, determine 

 currents of water to flow towards the mouth, 

 carrying with them the floating animalcules on 

 which the entire polypus subsists. 



Each mouth leads into a separate stomach ; 

 whence the food, after its digestion, passes into 

 several channels, generally five in number, which 



VOL. II. G 



