SUB-CLASSES LUCERXATtlDA, GRAPTOLTTin.E, ETC. 



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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 nuist 

 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 

 " CO vered - eyed " Mednsai differ considerably from one another in 

 their nature, and even in their structure, though they all present, in 

 spite of their usually greater size, a decided resemblance to the naked- 



Fig, 42. — Development of ^t(r(??(a, one of the iwccriiaj-uia. a Ciliated fi-ee-swiiiimiiig 

 embryo, or " planula " ; h Hyilra-tnlia ; c Hydra-tulja in which tiusi^in has consider- 

 ably advanced; d Hydra-tuba in which the lissiou has proceeded still further, 

 and a large number of the seguieuts have Iteen already detacheii to lead an in- 

 dependent existence. 



eyed Meduste already described. Some of the covered-eyed Mechixw 

 produce eggs which are developed into organisms resembling them- 

 selves ; but most of them are now known to be nothing more than 

 the free-swimming reproiluctive buds of minute rooted Ifi/i/roz<ia. 

 It will be sufficient 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 singular 

 animals, we find that the egg gives origin tij a little microscopic 

 ciliated body, which swims about freely l.iy means (jf tlie cilia with 

 which its surface is covered (fig. 42, a). This little Ijody, on finding 

 a suitable locality, fixes itself by one end, and develojjs a mouth and 

 tentacles at the other, when it is known as a " Hydra -tul;)a" (fig. 42, 



