324 EVENINGS AT THE MICBOSCOPE. 



in their successors with every wave, while the lowest seg 

 merits are scarcely visible as such. 



At length the extreme cup rocks and oscillates until the 

 slender thread of connexion is snapped, and it is free. It 

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

 downwards, and, contracting its margin with the well- 



TTJBRIS AND ITS YOUNG. 



known pulmonic spasm, shoots away with the movement as 

 well 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 dis- 

 covered, and which have been propounded under the title 

 of the Law of Alternation of Generations.* 



* See pages 338, 334, infra. 



