352 CONTRIBUTIONS TO THE NATURAL HISTORY 



of tlie vertical diameter upon the sides of the body, and, according to the direction 

 of its movements, be bent either towards the mouth or towards the anus, and thus a 

 foundation for their correct correspondence fairly introduced. Judging from the figures 

 of Mertens, it even appears that in the same genus this direction may be reversed ; for 

 in Beroe cucumis the tentacles are bent, and issue in the direction of the anal aperture, 

 as is also the case in B. compressa and B. octoptera, while in B. glandiformis it is the 

 reverse. May not this circumstance, however, coincide with some other differences in the 

 structure of those various species referred to Beroe, and indicate the propriety of separat- 

 ing them generically? Judging from Pleurobrachia when contrasted with Bolina and 

 Cydippe, we might infer that the tentacles were more and more developed in proportion 

 as they are removed from the mouth. But Leucothea shows that oral tentacles may be 

 as extensively developed as those which issue from the sides of the body. It is further a 

 question, which I am not, however, prepared to answer, how far the tentacles of Beroe 

 may be homologized with eitlier the tentacles around the mouth, or those around the disk, 

 of Discoid Medusae. From their connection with the chymiferous system, I should be 

 inclined to view the complicated branched tentacles of Beroe as corresponding to the 

 marginal tentacles of true Discoid Medusae, rather than as answering to the fringed lobes 

 which surround the oral aperture in so many of the latter. The position of these ten- 

 tacles with reference to the moutli bears some resemblance to what is noticed in the 

 position of the anus in the fiiniily of Echini, where the anus may open below very near 

 the mouth, or about the margin, or even on the upper surf^ice of the disk, directly oppo- 

 site to the mouth, without interfering with the general homology of those parts. 



After this digression, if we return to a more direct consideration of the form of Bolina, 

 we find that it differs from Pleurobrachia in the extraordinary development of two lobes 

 on its lower extremity (Plate VII. Fig. 1, 2, and 3), inclosing, when shut, the mouth and 

 its appendages, and extending transversely to the antero-posterior diameter, one forwards 

 and the other backwards, so that they contribute when expanded to increase the already 

 prominent length of the longitudinal diameter, leaving a deep transverse fissure between 

 them, at the bottom and centre of which the mouth is situated. The body thus shuts up 

 by the alternate approximation and separation of two valve-like lobes, hanging down- 

 wards, placed one in advance and the other backwards, in a position precisely inverse 

 to that of the valves of Acephala, which rest upon the sides of the body, and move 

 laterally. In addition to these two large broad lobes, there are on each side two smaller 

 ones, which arise from the main body at about the same height as the anterior and pos- 

 terior lobes, but which are simple short, narrow auricles converging or diverging alter- 

 nately, and thus shutting from the side, and above the great transverse fissure of the 



