122 DISCOPHOR^. Part III. 



extend to the pillars of the actinostome. The structure of these genital pouches is 

 well represented in Wagner's Icones Zootomicte, PI. XXXIII. Fiy. fi, but their rela- 

 tions to the tentacles are incorrectly drawn, the tentacles standing in the radial pro- 

 longation of the interval between the main lobe and the lateral lobes of each genital 

 sac. The difference between Pelagidaj and Cjaneidaj consists in this: that in Pela- 

 gidje the tentacles are in the indentations of the interambulacral lobes, which alternate 

 with ocular lobes ; while in Cyaneidte they are inserted upon the lower surface 

 of homologous lobes. These tentacular lobes are by far the most developed in 

 the Cyaneidaj, while in Pelagidae they have about the same dimensions as the 

 ocular lobes. The family may, therefore, be characterized thus : four ambulacral 

 pouches with one eye in the indentations between its marginal lobes, alternating 

 with four interambulacra, each of which consist of a medial or genital pouch with 

 one eye between its mai-ginal lobes, and two tentacular pouches, alternating with 

 the ambulacral pouches and the genital pouches. The radiating pouches of the 

 PelagidfB always terminate in simple marginal sacs, without dentritic ramifications, 

 while in all the Cyaneidte which have been carefully examined, they branch again 

 and again, forming the most elegant marginal ramifications. The genital pouches 

 remain suspended within the main cavity of the body, and do not form pendant 

 and flowing sacs, as in the Cyaneidje. 



From what I know of the mode of develojjment of the Pelagidte, it differs 

 essentially from that of the Cyaneidte; for in Pelagida3 the young, hatched from 

 the egg, passes directly into the ephyra form (PI. XII. Figa. 4, 5, 6,- 7, 8, 9, 10, 

 11, 12), while in Cyaneida3 it passes into the scyphostoma and strobila condition 

 before the ephyraj are developed. It follows, therefore, from the observations 

 which I have made iipon Pelagia Cyanella, that each egg produces only one 

 Pelagia, while it has long been known that in Cyanea and Aurelia each egg, being 

 transformed into a strobila, produces as many individuals as there are ephyraa 

 freeing themselves from the strobila. 



Besides Pelagia and Chrysaora, Gegenbaur also refers the genus Nausithoe to 

 the family of Pelagida?. I am, however, strongly inclined to consider this genus 

 as based upon young Pelagia?,. representing a stage immediately following that 

 which I have represented in PI. XII. Fig. 12, of the third volume of this work, 

 in which the tentacles are not yet developed, though the tentacular j^ouches 

 {^Fig. 12 a), Avhich alternate with the ocular pouches (i), jiist begin to be formed. 

 Should Nausithoe prove to be an adult animal, it would have to be considered 

 as a distinct family, inasmuch as it has no tentacular lobes, while all Pelagidae 

 have eight, alternating with eight ocular lobes. But a comparison between my 

 figures (PI. XII. Fig^. 3 and 12) readily shows, that while the young has eight 

 ocular lobes, each with two lappets, the adult has double that number of lappets. 



