74 DISCOPHORiE. Part III. 



shows them to arise between lobes of the disk (PI. VII. Figs. 1, 2, and 3), which 

 form, around their bases, as distinct sheaths as in the yEginida?. Moreover, though 

 in the adult Aurelia the radiating channels are tubular, in the young they are 

 flat pouches, as in the ^ginidse and Pelagidae. I have, therefore, no doubt that 

 the ^ginidaj must be removed from the order of the Hydroidte, and that they 

 are an embryonic type of the order of the Discophora3 proper, bearing to the higher 

 Discophora; the same relation as the simple, deciduous, medusse-buds of the Hydroids 

 bear to the more highly organized free naked-eyed MedusEe. The special homologies 

 of the ^ginidte to the young Aurelia and the lower PhanerocarpjB is most striking, 

 as a comparison of the plates of Gegenbaur^ with PI. XP. Fig. 4 may show. But 

 even when the young Aurelia has so far advanced in its development as to exhibit 

 all the prominent structural features of the genuine Discophorse it has not yet 

 assumed the true characters of its own genus, as they appear in the adult. In 

 the first place, the lobes of the eyes remain for a time more prominent than the 

 rest of the margin of the disk, and, in the second jilace, the tentacles are much 

 fewer than afterwards. In these respects our young Aurelia may, therefore, fairly 

 be comjiared to those genuine Discophoroe which, in their adult state, have prominent 

 ocular lobes and a few tentacles only, such as Nausithoe, Pelagia, and Chrysaora. 

 and even Sthenonia, though in the latter genus the tentacles are almost as numerous 

 as in the adult Aurelia ; but the ocular lobes preserve their prominence over the 

 tentacular lobes, while in Cyanea the tentacular lobes of the margin are the larger. 

 The fact that, in the young Aurelia, the tentacles appear rather like bunches than 

 like a marginal fringe, ought not to be overlooked ; and in this connection it may 

 be noticed, also, that the homology of the ocidar apparatus to the tentacles is most 

 satisfactorily traced in the young Aurelia (PI. XP. Figs. 2, 3, 4, and 17), where the 

 marginal lobules (/^) of the disk (see also, PI. VII. Figs. 2 and 3) correspond to the 

 lappets (y) of the ocular lobes, and the tentacles themselves {i^) to the eye {h) ; 

 a radiating chymiferous tube (c) penetrating into the peduncle of the eye, in the 

 same manner as into the tentacles. 



But this is not all : if the youngest Aurelia? resemble the ^ginidae, and the 

 more advanced young have striking affinities to the lower DiscophorjB, it is equally 

 certain, that the adult Aurelia resembles more closely the Rhizostomea^, than any 

 other genus of the Discophorae Semieostomeae does. This resemblance arises chiefly 

 from the structure of the oral appendages. In the Rhizostomeaj, the opposite margins 



^ See Gegenbaur, in Zeitscli. f. wiss. Zool. vol. of the mouth point in the direction of an inter- 



8, pi. 10, and V. Cams, Icones Zoologies, PI. II. ambulacrum, as is the case in this figure. Nor 



f. 17. I suspect that in this last figure the parts are the four bunches of tentacles of the sexual 



are not represented in their natural relations. I organs here symmetrically connected with the bunches 



do not know a single Acaleph in which the corners of ovaries, as they always are in nature. 



