(8) 



EXrLANATIOX OF THE PLATES. 



Fi-, 



Pl 



is entirely removed in the zone a' ; another is ent to 

 the base of the tentacles in the zone a : two others, in 

 the zones a" and a'", are cut very short ; and one, 

 between v" and o'", is preserved to a greater extent. 

 The eireiilar folds of the lower floor are entirely i)re- 

 served between the zones o" and o'" and in the zone 

 ((, and partially so in the zone a" and o. The radi- 

 ating folds are best seen in the zones o' o" o'", and 

 partially in the zone a. 



. 2 represents a part of the outer surface of the lower 

 lloor in connection with the oral appendages, a a being 

 the smooth membrane in the direction of the centre 

 of the ambulacra, as seen in fig. 1, in the zones o' 

 <)" and o'"; h h the radiating folds in the same zones; 

 c c the radiating folds in the interambulacral zones ; 

 (/ (/' and e the circular or concentric ti)lds, e being 

 in the ambulacral and <1 and d' in the interambu- 

 lacral zones ; 1 and 1 are the two pillars of one corner 

 of the mouth, to the right and left of wdiieh j)rojects 

 a sexual pouch : at 2 these pillars unite with the hori- 

 zontal and circular thickenings (3 and 4) of the oral 

 circle, and at o arise the folds of the oral lobes. 

 ;. 3 represents the marginal folds of the disk surrounding 

 the eye a he; a being the ambulacral tube of the 

 eye, narrowed in h, before reaching the eye proper e. 

 The wdiole magnified twenty-five diameters. 



A told of the margin of the oral lobes magnified 

 twelve diameters, to show the clusters of lasso-cells scat- 

 tered upon their inner surface ; one of these clusters 

 is magnified SoO diameters in lig. 4a. 

 ;. ,"j. A lobe of the margin of the disk to show the 

 ramifications of the chymit'erous tubes. 

 ;. (i. The margin of the disk folded downward over 

 the furrow in which the eye lies, to show the thick- 

 ness of the gelatinous upper layer of the nmlirella. 

 ;. 7. A portion of the lower floor of the disk, seen 

 from its upper or inner surface, to show how the cavity 

 of the tentacles opens into the main cavity of the 

 body. 



.\Tj; V. Besides many structural details relating chiefly 

 to the tentacles, this plate represents our C'yauea as 

 seen from above, with the margin fully expanded. 

 ^ 1 gives a general view from above, the animal resting 

 upon a dark ground. All the figures visible in this 

 drawing are the optical expression of the unecpial trans- 

 parency of the gelatinous mass of the disk, through 

 which shines the reddish-brown lining of the lower side 

 of its upper layer. In the centre appears a tessel- 

 lated, circular disk, which in adult specimens readily 

 separates from the peripheric part. The straight rays 



mark the deep furrows of the lower surface, radiating 

 from the central disk to the base of the eyes and to 

 the middle of the interambulacral zones; the ei"ht 

 longer rays being the ambulacral furrows, the eight 

 shorter ones the interambulacral fuiTows. The thicker 

 bands, converging and diverging again about half-way 

 their length, correspond to the thickenings of the gelati- 

 nous mass to which the lower floor of the disk is 

 attached; so that by this connection of the two floors 

 the main cavity of the body is divided into an open 

 circular central space and sixteen radiating tlat cham- 

 bers, the eight narrower of which, trending in the 

 direction of the eyes, are the ambulacral chambers, and 

 the eight wider ones alternating with them the inter- 

 ambulacral chambers. Upon comparing this figure with 

 fig. 1 of ri. 1\. it will be seen that the eight bunches 

 of tentacles conmumicate with the eight interambulacral 

 chambers; and that the four sexual pouches and the 

 four angles of the mouth face alternate ambulacral 

 chambers. 



Fig. 2 corresponds to fig. G of PI. IV., but represents the 

 same segment of the margin of the disk from the upper 

 side. This shows the eyes to be above the margin 

 of the disk, as the tentacles also are. 



Fig. 3 represents a band of the inner surface of the oral 

 lobes magnified, from the margin upwards ; showing 

 that along the margin the epitheliel cells ai-e smallest 

 and consist chiefly of lasso-cells, fig. 3d, while higher 

 up the lassos are in clusters, and the intervening epi- 

 theUel cells arc gradually larger and larger. On the 

 outer surface the lasso cells are few and tar apart. 



Fig. 4. Section of a tentacle, covered with clusters of 

 lasso-cells, showing its inner channel and the trans- 

 parent gelatinous wall. Slagnified 12 diameters. 



Fig. 5. Clusters of lasso-cells from the surface of a tenta- 

 cle. Magnified 230 diameters. 



Fig. (j. Other clusters of similar cells. Magnified 2.jO diams. 



Figs. 7, 8, 9, and 10. Segments of tentacles, magnified 

 GO diameters, showing different combinations of epi- 

 thelial cells and clusters of lassos. a indicates the 

 central cavity of the tentacles, and h the band of 

 longitudinal cells liy the contraction of which the tenta- 

 cles are shortened. 



Figs. 11 and 12. Cells lining the cavity of the tentacles. 

 Magnified 2.)0 diameters. 



Pl.^te V». Structiu-al details of Cyanea arctica. 



Fig. 1. Transverse section of the peripheric part of one 

 side of an ambidacrum, across the fm-row for the eye. 

 furrow for the eye ; a' a? sections of the chymife- 

 rous tubes. 



