450 



THE WONDER OF LIFE 



does not feed, so that not unnaturally it soon comes to 

 rest as if in fatigue. It fixes itself head downwards on the 

 rock or shell by means of its first pair of feelers and some 

 glutinous cement. It loses its bivalve shell and makes 



Fia. 72. Life-history of the common jelly-fish, Aurelia aurita. (After 

 Bronn.) 1, the free-swimming ciliated planula ; 2, the same fixed ; 

 3, the hydra-tuba, with four tentacles ; 4 and 5, the strobila or pile-of- 

 saucers stage ; 6, a later stage after most of the discs have been 

 separated off ; 7, a separated off disc or ephyra, showing 8 bifid 

 processes each with a sense-organ ; 8-9, the ephyra seen from the 

 side and from beneath. The mouth is shown in the centre. 



