AN EVENING AT THE MICROSCOPE. 191 



usually made to refer also to other Coelenterata or 

 hollow-bodied creatures. At the bottom of this 

 great class stand the Hydroid Zoophytes, of which 

 the hydra is the typical example. It consists of 

 a tubular or cylindrical body, which expands into 



FIG. M.Stwgs of Hydra. 



tentacles surrounding the mouth, its other end 

 terminating in an adherent disc or foot. The ten- 

 tacles are capable of great extension, and are used 

 as organs of prehension. The hydra has an extra- 

 ordinary power of multiplying, for even when 

 divided by any injury into a number of pieces, each 



