782 THE ANIMAL KINGDOM. 



The Scyphostoma passes in late autumn into the Strobila stage. A 

 circular furrow constricts the body on the aboral side of the tentacular circle, 

 cutting off a disc. A series of similar furrows appear one after another, 

 a basal pyriform portion of the body alone remaining undivided. The disc- 

 like segments thus cut off increase in diameter and are detached as young 

 Medusae or Ephyrae { Ephyrulae, Haeckel). In the first-formed segment 

 eight bifid marginal lobes grow out, each of which embraces the base of a 

 per- or an inter-radial tentacle x . These tentacles shorten, and their basal 

 portions are converted into the sensory bodies or rhopalia of the Medusa. 

 The eight adradial tentacles undergo complete atrophy. The gastric cavity 

 grows peripherally as four pouches separated by the four taeniolae, and a 

 perforation then takes place through the base of attachment of each taeniola 

 putting the pouches in communication. The gastric cavity extends out- 

 wards into each of the eight bifid lobes, which are much elongated. The 

 portions of the four taeniolae cut off are usually converted into gastral 

 filaments, and the taeniolar muscles are lost. The same eight bifid lobes 

 and the rhopalia appear in each of the remaining segments of the Strobila. 

 The basal pyriform portion of the Scyphostoma developes, sooner or later, a 

 set of sixteen tentacles, and after the detachment of the last Ephyra grows 

 in size. In spring it has been observed to pass again into the Strobila 

 condition. 



The Ephyra grows in size after its detachment. It may retain its 

 external appearance (certain Cannostomae). But with few exceptions it 

 undergoes changes of shape. The eight adradial intervals between the 

 eight marginal lobes increase much in extent, and either remain simple, or 

 are divided into a number of lobes, simple or bifid. The lobes in question 

 are either independent outgrowths of the bell-margin, which may or may 

 not divide, or are produced by fission (i) from the sides of the Ephyra 

 lobes, and (2) of the lobes thus derived. The bell itself is somewhat 

 flattened, of greater breadth than depth. It is sometimes divided into a 

 central and peripheral portion by a circular furrow in the exumbrella, the 

 fossa coronaris. Its margin never becomes inflected inwards : when it is 

 thin and velum-like, as e. g. in Aurelia, it is termed by Haeckel * velarium.' 

 The mouth retains its square outline in Cannostomae, or its four angles are 

 prolonged outwards into four oral arms, with a deep adoral furrow lined by 

 endoderm and folded edges in Semostomae\ and in Rhizostomae these 

 four arms become bifid at their apex during growth ; the edges of their 

 furrows become much folded and produced into processes ; the surfaces of 

 the folds and processes concresce from place to place, leaving only funnel- 

 shaped openings, which lead into the adoral furrows now converted into 



1 Haeckel in his System and elsewhere appears always to count the two divisions of these 

 lobes as separate lobes. He terms them subradial, the tentacles intervening between successive 

 pairs being adradial. 



