JELLY-FISHES. 



And now, reverting to the Hydrae and Jelly-fishes described 

 in the few last pages, so diverse in their forms and attributes, 

 the reader perhaps begins to wonder what relationship exists 

 among them that they should thus be classified as members of 

 the same great family; and this we must next proceed to explain. 

 Any one who will examine, with a little industry, the surface 

 of the stones, or shells, or rocks upon the shore, just at the lowest 

 point of the ebb-tide, will probably observe, clinging to their sur- 

 face, numerous delicate white tufts or tassels, every one of which, 

 examined closely, is found to be a hydra, scarcely different in its 

 form or habits from that we have described in a preceding page. 

 This marine hydra has received the name of Hydra tuba : it 

 quite equals in voracity its fresh-water namesake, is equally for- 

 midable in its armature of 

 lasso-threads, and is ordina- 

 rily multiplied in the same 

 manner by buds or gemmae 

 that sprout from its surface : 

 at certain seasons, however, 

 he body of the Hydra tuba 

 becomes considerably elong- 

 ated, and divided by constric- 

 tions into numerous segments 

 resembling a pile of saucers 

 placed one within the other. 

 Shortly, from the margin of 

 each saucer, tentacles are 

 seen to sprout, not resembling those of the hydra, but those of the 

 Medusae, and after a little while these saucers, detaching them- 

 selves successively from the top of the pile swim away, completely 

 formed and active Acalephae (Fig. 30). 



The Campanularian Zoophytes (Fig. 22), as we have explained, 

 produce their young in elegant transparent vases, which sprout 

 from the bases of their Polype-bearing branchlets ; yet, when 

 these vases open, they send forth, not ciliated embryos, as is the 

 case with the Sertularian Polypes (Fig. 21), but Acalephs, that 

 swim about like little parachutes, cast out by thousands into the 

 surrounding water. On the other hand, the young of the Medusae 

 are found, in the first stage of their existence, exactly to resemble 

 hydriform Polypes proving at least the existence of 'a relation- 

 ship among them, although its extent is as yet very imperfectly 

 understood. Still, we are now sufficiently acquainted with the 



i'lG. 30. TUKKIS AND ITS YOUNG. 



