LIFE-HISTORY OF AURELIA. 135 



inch in height. It may give rise to other larvae like itself 

 by lateral buds near its base, or by the formation of creeping 

 stolons from which buds are given off. This process must 

 be distinguished from the multiplication by which the larva 

 gives rise to the adult forms. 



In late autumn, a remarkable change occurs. The scyphi- 

 stoma elongates, and an annular constriction below the 

 tentacles begins to separate off what lies above. Below the 

 uppermost constriction another is formed, and gradually a 

 dozen or more of these rings appear. This stage, often 

 compared to a pile of saucers, is technically called a strobila. 

 Each disc is separated off in its turn as a free-swimming 

 Ephyra which becomes a jellyfish. The still undivided 

 basal portion may rest awhile and then undergo further 

 constriction. 



The first Ephyra differs from those which come after it, 

 since it bears the original tentacles of the Hydra-tuba. 

 From its margin eight bifid lobes grow out, each embracing 

 the base of a perradial or interradial tentacle. The bases 

 of these eight tentacles become the sense-organs or rhopalia. 

 The other eight (adradial) tentacles atrophy. On the 

 Ephyrse which follow there are at first no tentacles — only 

 the eight bifid marginal lobes which bear the sense-organs in 

 their niches. The liberated Ephyrae grow rapidly, undergo 

 some structural modifications, and eventually become small 

 jellyfish. 



Here, again, alternation of generations is illustrated. 

 From the fertilised ovum, a fixed asexual Scyphistoma 

 results. This grows into a Strobila, from which transverse 

 buds or Ephyree are liberated. Each of these grows into 

 asexual Aurelia — producing ova or spermatozoa. 



It is probable, as Hatschek suggests, that the Scyphistoma 

 originally rested for a while and then floated off to become 

 an adult. We may suppose this primitive life-history to have 

 been succeeded by one in which the Scyphistoma divided 

 transversely and set free one Ephyra, after which it rested, 

 regained its tentacles, and then produced another, and so on 

 in rhythmic succession. The " strobilation " or production 

 of many Ephyra in rapid succession, seems to represent an 

 abbreviation of the primitive mode of development. 



Near Relatives of Aurelia. — The common jellyfish is 



