116 DISCOPHORiE. Part III. 



constitute its generic characteristics. For, unless attempts are made to analj'ze 

 the meaning of the facts observed, zoijlogy will forever retain a purely descriptive 

 character, and never assume the true dignity of science. That the Cyaneidaj con- 

 stitute a distinct family has already been shown, and yet, unless the genus Cyanea 

 is carefully contrasted with certain genera of other families, it may not always 

 be easy to distinguish it from them. A Phacellophora, for instance, floating in 

 the water, must have a very striking resemblance to a Cyanea, judging from the 

 figures of Mertens published by Brandt. For in that genus the actinostome is 

 very large, the genital pouches form pendant sacs, of considerable size, and the 

 tentacles, of large dimensions, are grouped in Inmches on a crescentrshaped base 

 of insertion, at some distance from the margin, and must, therefore, present an 

 asjDCct quite similar to that of our Cyanea. But as soon as we consider the 

 relations of their structure to their form, we find the greatest difference between 

 them. In the first place, the chymiferous cavities, which radiate from the main 

 central cavity, are broad pouches in Cyanea, terminating in rounded lobes at the 

 margin. In Phacellophora they consist of numerous radiating tubes, ramifying 

 towards the margin, in a manner similar to, and yet distinct from, Aurelia; for here 

 the simple tubes are those which correspond to the bunches of tentacles, and the 

 branching tuljes those which terminate in the intervening lobes of the margin of 

 the disk, wlide in Aurelia it is the reverse. Moreover, there are, in Phacellophora, 

 four bunches of tentacles in each interambulacrum ; namel}^, two bunches on each 

 side of the chymiferous tubes, radiating from the middle of the genital pouches, 

 while in Cyanea there is only one bunch on each side of the genital pouches. The 

 total number of the large bunches of tentacles is, therefore, sixteen in Phacello- 

 phorae, beyond which projects a rounded lobe of the margin of the disk. There 

 are, further, sixteen three-leaved lobes, alternating with the tentacular lobes ; four 

 in the prolongation of the corners of the mouth ; four in the prolongation of the 

 middle of the genital pouches, and eight corresponding to the angles of the genital 

 pouches. Whether all these have eyes, or only those in the prolongation of the 

 angles of the mouth and of the genital pouches, cannot be ascertained from the 

 figures of Mertens. 



The genus Heccaedecoma, which belongs to the same family as Phacellophora, 

 has, in some respects, a still greater general resemblance to Cyanea, and is consid- 

 ered by Brandt simply as a sub-genus of Cyanea; and yet I am satisfied that 

 it does not even belong to the same family, for, like Phacellophora and Sthenonia, 

 it has branching chymiferous tubes, extending from the main cavity to the margin 

 of the disk, instead of pouches as Cyanea has ; but it approximates Cyanea more 

 by the structure of its actinostome, which consists of four thin, flowing curtains. 

 The margin of the disk is also very differently scalloped, consisting of sixteen 



