Chap. III. ACTINAL SYSTEM OF CYANEA. 103 



An examination of the arrangement of the tentacles may readily be made by 

 cutting them off at their base, as in PI. IV. Fig. 1 a, or by an inspection of the 

 inner svu-face of the lower floor, PI. IV. Fig. 7, where the round apertures, arranged 

 in rows, indicate the lumen of the tentacles. It is then seen, that those nearer 

 to the concentric and radiating folds are the larger ones, and those more outward, 

 towards the margin, the smaller ones; while it also appears that these rows, which 

 follow the outlines of the folds, form, in their combination, a crescent-like figure, 

 the arms of which are but slightly open. This, again, explains the peculiar appear- 

 ance of the bunches, as seen in Plate III., in which the two middle bunches are 

 visible from the outside, so that the smaller and shorter tentacles are in front, and 

 the larger and longer ones further backward, in the convex part of their surface 

 of attachment; while the lateral bunches of the same figure are brought to view 

 in such a position that the part nearer the middle biuiches is seen from the inner 

 side of the crescent-shaped surface of attachment, and the further part, from its 

 outside. The aspect presented by all these tentacles, taken as a whole, is further 

 rendered more varied by the difference in their color; the majority of them ai-e 

 of a 2)urplish-red tint, similar to that of the surfiice of the disk, but there are 

 always a number which have a more yellowish, or orange tint, and others which 

 are more reddish, and when all tentacles are in full play, the changes of color 

 add greatly to the effect of the motion. 



A comparison of the tentacles with the folds of the lower floor discloses, between 

 them, an unexpected resemblance, which can leave no doubt in the mind that, after 

 all, the most diversified oi-gans of these animals are only modifications of very 

 simple structural elements. Like the folds and the lower floor itself, the tentacles 

 consist of two distinct layers of cells, between which there is a larger or smaller 

 amount of the characteristic gelatinous mass of the Acalephs, and the chief differ- 

 ence between the tentacles and the pouches of the folds consists in their form, 

 as Fig. 7 of PI. IV. shows. In the folds, the cavities are the result of straight 

 plications, intersecting one another, and thus forming angular sacs, projecting but 

 slightly ; in the fields occupied by the tentacles, which are immediately adjoining 

 the folds, we have similar pouches, with rounded outlines, projecting enormously in 

 the shape of hollow cylinders, and lined by a prolongation of the inner layer of 

 the floor, while the outer surface is the direct prolongation of the outer layer. 

 Between these two layers there ax-e larger or smaller masses of gelatinous substance, 

 varying in thickness near the base of the tentacle, or between the folds of the 

 pouches, according to their various stages of development with an advancing age. 



The genital pouches themselves share this structure, being, in fact, large sacs, 

 formed by a projection of the whole thickness of the lower floor, between the 

 pillars to which the actinostome is suspended ; PL IV. Fig. 2, and PI. V^ Fig. 15, 



