228 GROWTH OF THE 



rising to the surface, they cast aside their skin, with its 

 gills and fins, and thenceforward breathe the air through 

 which they fly. Similar changes we have already noticed 

 in the Crustacea, and such we may have to speak of in 

 other classes of animals, but these are not of the same 

 nature as what we have now to describe as taking place 

 in the ACALEPH.E, or Jelly-fishes. The insect deposits 

 an egg, and each egg will, in due time, produce an in- 

 sect similar to its parent, and nothing more. But the 

 Jelly-fish throws off organized bodies, which can scarcely 

 be called eggs, but which may more justly be compared 

 to the gemmae or buds of a plant ; for, from every one 

 of them may spring a whole colony of Jelly-fishes. The 

 extraordinary history of these creatures was first ascer- 

 tained by M. Sars, a celebrated Swedish naturalist. The 

 English reader may find a more detailed account than is 

 here given in Steenstrup's " Alternation of Generations," 

 published by the Ray Society, and in a very interest- 

 ing memoir by Dr. Reid in Taylor's " Annals." * 



Without adopting all the theoretical inferences de- 

 duced from the "alternation of generations," we may 

 state the facts as follows. The Medusa gives birth to 

 a multitude of minute gelatinous bodies, in shape not 

 very unlike the so-called eggs of a sponge, or the spores 

 of one of the lower Algse, and, like them, furnished 

 with a multitude of cilia, or vibratile hairs, which 

 clothe the surface, and by their motion propel the little 

 body through the water. These active little bodies 

 must, I think, be looked upon as gemmae or buds, rather 



* " An. Nat. Hist." (1848), p. 25, &c. See also Forbes's " Mono- 

 graph of the British Naked Eyed Medusae, Ray Society," 1848. 



