252 CONTRIBUTIONS TO THE NATURAL HISTORY 



The origin of the four chjmiferous tubes, which arise from the upper corners (Plate 

 I. Fig. 1) of this cavity, shows still further the intimate relation there is between the 

 structure of Hippocrene and that of the other genera of the family. Perhaps the ar- 

 rangement of the tentacles might be a more difficult point, as in Sarsia we have only 

 one long tentacle, with one eye-speck at the confluence of the vertical and circular tubes; 

 while in other genera, such as Tiaropsis and Staurophora, there are many isolated tentacles 

 all round the lower margin of the disk, larger ones alternating with smaller ones, either 

 each provided with an eye-speck, or only the larger ones, or the eye-specks alternating 

 with the tentacles. But if we take into consideration the curious genus Lizzia, of Forbes, 

 where there are alternately two and three tentacles more closely united, with a single 

 eye-speck to each bundle, there will be no longer any difficulty in acknowledging in 

 Hippocrene only an extreme in the combination of tentacles, grouped altogether in four 

 bunches, with the additional peculiarity of having as many eye-specks as there are ten- 

 tacles ; — an extreme, I say, of the arrangement foreshadowed in Lizzia, where fewer 

 tentacles form similar bunches. Thus we are gradually led to consider as belonging to 

 the same series those naked-eyed Medusae in which the tentacles are arranged in a single 

 row, as Thaumantias, Willia, Circe, Oceania, Tunis, Stomobrachium, Geryonia, and 

 Geryonopsis ; and those in which they are combined in bunches, as Lizzia and Hippo- 

 crene ; and those in which they are reduced to a few isolated tentacles, as in the genera 

 Sarsia, Slabberia, and Modeeria ; and even those in which there is one single tentacle 

 developed, as in the genera Euphysa and Steenstruppia. 



A thorough comparison of the other generic peculiarities throughout this family will 

 sustain equally well my position, that the naked-eyed Medusae constitute a single natural 

 family; and that the modifications noticed in different genera are only generic modifica- 

 tions, and not indications of distinct families. The fact that the tubes branch before they 

 reach the circular tube, as is the case in Willia, is of no greater importance than the 

 fact, that individuals of the same species may have a larger or smaller number of such 

 tubes. For though generally the number of these tubes is constant in one and the same 

 species, we have seen Sarsia mirabilis with six rays, six tubes, six tentacles, and six eye- 

 specks, and the bundles of muscles follow the same general arrangement, according to 

 the fundamental number displayed in those specimens, just as the number four prevails 

 in others. Of how subordinate importance this ramification of tubes may be will ap- 

 pear still more evident, when we take into consideration the diversity there is in that 

 respect among the common discoid Medusae. And, also, to refer to genera of this very 

 family, we cannot but be struck with the little importance of these ramifications as the 

 foundation for families, when we compare the genera Berenice, Staurophora, and Eudora. 



