JELLY-FISHES 367 



in their successors with every wave, while the lowest seg- 

 ments are scarcely visible as such. 



At length the extreme cup rocks and oscillates until 

 the slender thread of connection is snapped, and it is free. 

 It at once turns itself over, so as to present its concavity 

 downward, and contracting its margin with the well-known 

 pulmonic spasm, shoots away with the movement as well 



TURRIS AND ITS YOUNG. 



as the form of a veritable Medusa. The little progeny 

 has, at length, after passing through so many changes, 

 returned to the image of its parent. 



Such are, in brief, the phenomena of one of the most 

 remarkable series of facts that modern zoology has discov- 

 ered, and which have been propounded under the title of 

 the Law of Alternation of Generations. 



