LUCEKNAEIDA AND GRAPTOLITID^. 



79 



Another type of the Lucernarida is represented by the 

 organisms formerly termed " hidden - eyed " Medusce, and 

 familiarly known as sea-nettles or sea-blubbers. Every sea- 

 side visitor is familiar with the great circular disks of jelly 

 which are left upon the sands by the retreating tide during 

 the summer months ; and many must have noticed on a calm 

 day the large, transparent disks of these same creatures slowly 

 flapping their way through the water. Not a few, too, must 

 have learned by painful experience that some of these singular 

 organisms have the power of stinging most severely, if in- 

 cautiously handled. The forms included under the old name 

 of " covered-eyed " Medusae differ considerably from one an- 

 other in their nature, and even in their structure, though they 

 all present, in spite of their much greater size, a decided re- 

 semblance to the naked-eyed lledusce already described. Some 

 of the covered-eyed Medusce produce eggs which are developed 

 into organisms resembling themselves ; but most of them are 

 now known to be nothing more than the free-swimming re- 

 productive buds of minute rooted Sydrozoa. It will be suf- 

 ficient here to describe shortly the life-history of one of the 

 more remarkable forms of this section. 



If we commence with the young form of one of these sin- 



FiG. 23. — ^Deyelopment of Lucernarida (^Chrysaord). a Ciliated embryo; 6 Hydra-tuba; 

 c Hydra-tuba beginning to divide by transverse cleavage ; d The cleavage stiU further 

 advanced ; e A form in which the cleavage has proceeded still further, and a fresh circle 

 of tentacles has been produced near the base; /Free-swimming, generative zooid, pro- 

 duced by fission from the Hydra-tuba. 



gular animals, we find that the egg gives origin to a little 

 microscopic ciliated body, which swims about freely by means 

 of the cilia with which its surface is covered (Fig. 23, a). 



