Chap. III. ACTINAL SYSTEM OF CYANEA. 99 



wliich hang down from its surface, we have first to consider its appearance as an 

 horizontal curtain, stretched froni the margin of the disk to the outUne of the 

 actinostome. For some distance from the margin, inward, it is everywhere a com- 

 paratively thin, gelatinous membrane, with a smooth surface, connected with the 

 upper floor by innumerable branching bridges, intercepting narrow channels, which 

 communicate freely with the pouches of their respective areas, as seen PI. V\ Figs. 

 23 and 24, and PI. IV. Fi(/. 1. It would require a slight extension in the length 

 of these bridges, in the direction of the main cavity, to transform all the channels 

 which they inclose into a system of radiating tubes, similar to those of Aurelia 

 or of Khizostoma and Polyclonia. The pouches themselves must, therefore, be con- 

 sidered as homologous to chymiferous tubes. They are, in reality, wide-sjireading 

 chymiferous tubes, branching only at their peripheric termination, and resemble, in 

 this respect, the chymiferous tubes of the young ephyra of Aurelia, as represented 

 PL XP. Figs. 4 and 17. 



■ In the spaces of the lower floor, not occupied by the tentacles, the genital 

 pouches, and the actinostome, the lower floor is not only thicker than along the 

 margin, but it is also folded in a very peculiar manner. Some of the folds trend 

 in the direction of the ambulacral and interambulacral pouches themselves, that is, 

 from the centre towards the periphery ; while others are concentric. All these 

 folds are combined into well-defined systems. PI. IV. Figs. 1 and 2, shows their 

 distribution. Between each narrow j'ouch and the adjoining broad pouch, there 

 is a bundle of radiating folds, each of which is i-eadily seen to consist of two 

 halves, the longer of which (PI. IV. Fig. 2 h) flanks the narrow pouches, while the 

 shorter (c) surrounds the bundles of tentacles from the side. The concentric folds, 

 on the contrary, occupy, alternately, wider and narrower areas, in such a way that 

 the narrow areas are stretched across the actinal termination of the ambulacral 

 pouches and of the middle pouches of the interambulacra, PI. IV. Fig. 2 e, while 

 the broader areas cover the actinal part of the tentacular pouches, upon which 

 they do not advance in a triangular prolongation, as the narrow areas do, but 

 form a straight border to the actinal part of the field occupied by the tentacles. 

 Towards the part of the lower floor immediately adjacent to the genital pouches, 

 the concentric folds are continuous, and present none of the interruptions which 

 further outside divide them into distinct areas. In fact, the lower floor", immediately 

 outside of the actinostome, is a smooth membrane, as near the margin, and from 

 this smooth floor hang the genital pouches, as sacks folding downwai'ds, PL IV. 

 Fig. 1, and the peduncle of the actinostome, PL IV. Fig. 2 11; while outside of 

 the genital pouches the floor is gradually drawn into more and more distinct, 

 continuous, circular folds {Fig. 2 d'), and becomes divided into distinct areas of 

 concentric folds further outward [d). These divisions arise from the manner in 



