224 ROBERT PAYNE lilGELoW ON 



movements arc rapiil .nid violent. The rliytlini is iiitenn|iteil liy few pauses, and tliese 

 are short. The result nl' these movements is tliat the thin wall of the isthmus is 

 ruptureil, and the ephyrula is set free. 



AftiT tins separation, the basal polyp has the ap[)eaiancc i-e|iresented in Figs. Ii7 and 

 28. It is a scyphistunni with seventeen short tentacles and a rudimentary proboscis 

 (Figs. (Jl and 62). The proboscis and the tentacles grow rapidly, so that in a few days 

 it is inijiossible to distinguish a regenerated basal polyp from a young scy|)histoma in the 

 sixteen-tentacle stage, except that the former has a souiewhat thicker stem. It nniy be 

 inferred from this complete regeneration of the basal polyp that it undergoes repeated 

 strobilization, as Clans' has found to be the case in x\urelia. 



The Ephyruld. — The ephyrulaof Cassio|iea is very different in appearance from the 

 corresponding stage in ordinary scj'phomednsae with eight rhopalia. Cotylorhiza has an 

 ephyrula rescMubling the same stage in tlu! senmstonuitous medusae. Good figures of 

 this are given by du Plessis and Clans, and there is a striking difference between these 

 figures and Figs. 29 and oO in this paper, which are camera drawings of well-preserved 

 ephyrulas of Cassiopea, mounted in balsam. Fig. 2U rejiresents a young Cassiopea tiiat 

 has not long enjoyed a free existence. The general shape of the undirella is like that of 

 the adult, and there is the same concavity in the centre of the exumbrella, while the 

 margin curves in the opposite direction, as in Fig. 64. The typical eph3a-ula of Aurelia 

 or Cotylorhiza has eight marginal arms with two lobes at the end of each, and between 

 each pair of lobes there is a rhopalium. In Ca.ssiopea. structures coi'responding to these 

 arms are present to the number of sixteen, or often more. But these do not destroy the 

 general circular outline of the animal, for they are connected by thin areas on the 

 undjrella, alternating with an e(|ual number of ridges, which at an earlier stage bore the 

 interrhopalial tentacles on their under sides. 



We have, then, at this stage the marginal zone of the umbrella marked by a number 

 of short radial ridges separated by an equal number of thin areas. The ridges are in 

 line with the radial canals. At the peripheral end of each ridge the margin of the 

 umbrella is produced into two lobes, those adioiiiing the rhojialia being well marked, 

 the others small and inconspicuous (il. Fig. 30). 



In Fig. 21) there are seventeen, and in Fig. 30, twenty-three, rhopalia. The latter 

 is an unusually large number, an<l it will be noticed that the nundjer of marginal lobes 

 has not increased in proportion, so that irregularities of the margin occur in many places, 

 as described in the section on variations. 



At this stage the rhophalia have come to lie, as in the adult, wholly within the margin 

 of the umbrella, and project from its subumbrellar surface. Tiie interrhopalial tentacles 



'Sec foot-iioU', CUui.s ('92). 



