84 INVERTEBRATE ANIMALS. 
Another type of the Lucernarida is represented by the organ- 
isms formerly termed “hidden-eyed” MZeduse@ and familiarly 
‘known as sea-nettles or sea-blubbers. Every sea-side visitor is 
familiar with the great circular discs 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 discs of these same creatures slowly flapping their 
way through the water. Not a few, too, must have learnt by 
painful experience that some of these singular organisms have 
the power of stinging most severely, if incautiously handled. 
The forms included under the old name of “covered-eyed ” 
Medus@ differ considerably from one another in their nature, 
and even in their structure, though they all present, in spite of 
their much greater size, a decided resemblance to the naked- 
eyed Meduse already described. Some of the covered - eyed 
Meduse produce eggs which are developed into organisms 
resembling themselves; but most of them are now known to 
be nothing more than the free-swimming reproductive buds of 
minute rooted Hydrozoa. It will be sufficient here to describe 
shortly the life-history of one of the more remarkable forms of 
this section. 
Fig. 28.— Development of Lucernarida (CArysaora). a Ciliated embryo; & Hy- 
dra-tuba; ¢ Hydra-tuba beginning to divide by transverse cleavage; d The 
cleavage still further advanced ; ¢ A form in which the cleavage has proceeded 
still further, and a fresh circle of tentacles has been produced near the base ; 
J Free-swimming generative zodid, produced by fission from the Hydra-tuba. © 
If we commence with the young form of one of these singular 
animals, we find that the egg gives origin to a little microscopic 
ciliated body, which swims about freely by means of the cilia 
