72 DISCOPHOR^. Part III. 



ization, the spherosome of which is largely charged Avith calcareous spiculse. I 



would add, that, cousidering all these relations of the two classes, the Echinoderms 



appear to me as closely related to the Acalephs, as the Acalephs are to the 



Polyps, and so completely built upon one and the same plan, that it is out of 



the question to regard them any longer as the representatives of two distinct, 

 primary divisions of the animal kingdom. 



SECTION V. 



CLOSER AFFINITIES OF AURELIA. 



As soon as the ephyrae have freed themselves from the strobila stock, they lose 

 rapidly their hydroid affinities. We have seen, in a former paragraph, how intimate 

 the relations of all the parts of an Ephyra are to those of the Scyphostoma, from 

 which they are derived. An ephyra, properly speaking, is only a transverse seg- 

 ment of a scyphostoma, which has become independent of the stem from which it 

 was once a part. But as soon as it has accomplished its liberation, new tendencies 

 are manifested, leading towards new affinities, not perceptible in the strobila state. 

 The ephyra grows to be a genuine Discoid medusa, with all the structural character- 

 istics of the DiscophorJB proper. As a free ephyra, however, it is already a Medusa 

 and no longer a Hydroid; and it is interesting now to look back upon the time 

 when the origin of the EphyrsB was unknown, and to consider what place was 

 then assigned to them in the system. They were, for a long time, considered 

 as an independent genus among the Discophora3. When a naturalist, so extensively 

 acquainted with the Acalephs as Eschscholtz was, found it natui'al to separate the 

 Ephyra, as a genus, from the genus to which he referred the adult Aurelia, and 

 to place it at the end of the family of the Medusida?, in the immediate vicinity 

 of the naked-eyed Medusa?, this is significant, as indicating the great difference 

 existing between the young and the perfect Medusa; but it also marks the direc- 

 tion in which the difference points : it is towards the lower Discophora?, the Crypto- 

 carpa? of Eschscholtz, which I propose to unite with the Hydroids. Yet, even 

 at this early period of its existence, our Aurelia shows already signs of its true 

 affinities; for, as soon as the sexual organs begin to be formed, they occupy dis- 

 tinctly an interambulacral position, as in all genuine Discophorse, and do not follow 

 the course of the radiating chymiferous tubes, as in the naked-eyed Medusae. The 

 points in which the younger ephyrje agree more nearly with the Cryptocarpae 

 than with the Phanerocarpa?, are the direct origin of the chymiferous tubes from 



