92 THE STORY OF LIFE IN THE SEAS. 



parent or on that of the little larvrge when they 

 are first hatched. 



Thus we find in the body of the Copepods at 

 least two important modifications of structure, 

 which render them fit or suitable for their life- 

 long swim in the surface waters of the sea. 



Let us now consider another important group 

 that has the same habit but differs from the 

 Copepods in size and form, namely, the Jelly- 

 fish. 



The Jelly-fish, or Medusae, as they are usually- 

 called by zoologists, are disc or bell-shaped ani- 

 mals of a very soft gelatinous texture. From the 

 centre of the disc or bell there hangs down a tube 

 of varying length bearing the mouth, and the 

 margin is often provided with a row of thin 

 delicate tentacles like a fringe. (See Fig. 7). 

 When watched on a calm summer's evening they 

 may be seen to slowly sink a few inches or more 

 from the surface, and then with a series of con- 

 vulsive contractions of the bell to rise to the 

 surface again. Sometimes these contractions 

 may be observed to continue perfectly rhythmi- 

 cally for a long time. 



In one of the commonest of the English 

 Medusae four rings of a bright pink or orange 

 colour may be observed in the disc. These are 

 eggs and male spawn, and when shed they give 

 rise to multitudes of tiny little larvae which sink 

 to the bottom and become fixed to some rock or sea- 

 weed. After the larva has securely fixed itself 

 it becomes changed into a little Polyp which 

 gives rise, in the course of time, to a number of 

 small discs, arranged one above another like a 



