MARINE BIOLOGICAL STATION AT PORT ERIN. 



75 



fore merely free-swimming stages in the life-history of 

 Hydroid Zoophytes, and these are frequently spoken of as 

 " Mednsoids." Some of our larger Medusae, however, 

 such as the Aurelia shown in fig. IY. are not produced as 

 buds on a fixed Zoophyte colony, but have a somewhat 

 different life-history. As fig. IY. shows, the fertilised egg 

 of an Aurelia becomes an ovate free-swimming embryo 



Fig. IV. 



which settles down and grows gradually into a Hydra-like 

 Zooid with a mouth and long tentacles. Then the body 

 becomes transversely constricted and divided into many 

 pieces, which, when completely separated, lie like a pile of 

 saucers or soup-plates. As they float away from the pile 

 each such " Ephyra " is seen to be a little Medusa, and 

 they grow into young Aurelias. 



