256 ALTERNATE GENERATIONS. 



various phases of this extraordinary series of 

 metamorphoses, so different from each other in 

 their external aspects, should not have been 

 recognized at once, and that this singular Aca- 

 leph should have been called Scyphostoma in its 

 simple Hydroid condition (see p. 248), Strobila 

 after the transverse division of the body had taken 

 place (see p. 249), Ephyra in the first stages of 

 its free existence (see p. 251), and Aurelia in its 

 adult state (see pp. 252 and 254), being thus 

 described as four distinct animals. These vari- 

 ous forms are now rightly considered as the suc- 

 cessive stages of a development intimately con- 

 nected in all its parts, beginning with the 

 simple Hydroid attached to the ground, and clos- 

 ing in the shape of our common Aurelia, with 

 its white transparent disk, its silky fringe of 

 tentacles around the margin, its ruffled curtains 

 hanging from the mouth, and its four crescent- 

 shaped ovaries grouped to form a cross on the 

 summit. From these ovaries a new brood of 

 little embryos is shed in due time. 



There are other Hydroids giving rise to Me- 

 dusa buds, from which, however, the Medusae 

 do not separate to begin a new life, but wither 

 on the Hydroid stock, after having come to ma- 

 turity and dropped their eggs. Such is the Hy- 

 dractinia polyclina. This curious community 

 begins, like the preceding ones, with a single 



