72 THE VITAL FUNCTIONS. 



the body of one hydra is introduced into the mouth 

 of another, so that their lieads are kept in contact 

 for a sufficient length of time, they unite and form 

 but one individual. A number of heads and bodies 

 may thus be joined together artificially, so as to 

 compose 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 pro- 

 lific 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 ex- 

 tended floweiing 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 stationary condition of these 

 polypes prevents them from moving in search of 

 food, their tentacula are generally furnished with a 

 nmltitude of cilia, which, by their incessant vibra- 

 tions, determine currents of water to flow towards 

 the mouth, carrying with them the floating animal- 

 cules on which the entire polypus subsist^. 



Each mouth leads into a separate stomach ; 

 whence the food, after its digestion, passes into 

 several channels, generally five in number, which 

 proceed in different directions from the cavity of 

 each stomach, dividing into many branches, and 

 being distributed over all the surrounding portions 

 of the flesh. These branches communicate with 

 similar channels proceeding from the neighbouring 

 stomachs : so that the food, which has been taken 

 in by one of the mouths, contributes to the general 



