292 CONTRIBUTIONS TO THE NATURAL HISTORY 



ing, more deeply cleft in sinuous outlines, instead of the regular dichotomal division which 

 characterizes it ; or if we could conceive the proboscis of Sarsia (Plate IV. Fig. 1) to be con- 

 tracted within the main cavity of the gelatinous bell, to be shortened to about one fourth 

 of the diameter of the main gelatinous disk, somewhat more than is represented in Plate 

 V. Fig. 10, to be split about the opening, and the power of motion to be limited within 

 this margin, rather than to extend to the whole cavity ; then it would be seen how 

 closely indeed these three genera resemble each other in the structure of their alimen- 

 tary apparatus, notwithstanding the striking difference in its outlines. But it is impor- 

 tant that such comparisons should be made, in order that we may fully understand that 

 there is no difference — no organic difference — between those Medusae which have a 

 long proboscis, and those which have apparently none. This is the more important, as 

 various authors have classified the Medusae, and subdivided them upon the ground of the 

 existence or absence of a proboscis ; but we shall presently see that in such classifica- 

 tions Staurophora, Berenice, and other genera are entirely removed from the vicinity of 

 Sarsia, Thaumantias, and Tiaropsis, when in reality they should be placed side by side, as 

 I may show hereafter. 



I have failed to trace nettling cells around the margin of the oral fringes and upon 

 the tentacles of Tiaropsis, though I hardly doubt that they exist, with all the complica- 

 tion of the various kinds of lassos characteristic of all the appendages employed by these 

 animals in securing their prey. 



The main central cavity of the digestive apparatus is very small (Plate VI. Fig. 9, 

 seen in profile, 10, seen from below, and 11, seen from above). It is a rather narrow 

 funnel, divided into four tubes, radiating at right angles along the inner surface of the 

 gelatinous disk, towards the margin of the animal. These tubes are funnel-shaped 

 (Fig. 9, d) where they arise from the central cavity, but are soon narrowed into 

 uniform tubes, extending Avithout modification to the margin of the disk. The re- 

 lations between these four chymiferous tubes and the circular tube of the lower mar- 

 gin of the gelatinous disk are precisely identical in the genera Tiaropsis, Sarsia, and 

 Hippocrene. There is the most free communication between them. The chyme is 

 circulated to and fro from the central cavity into the radiating tubes, and from these 

 into the circular tube, and vice versa. There is, however, this marked difference be- 

 tween the three genera, that in Sarsia there is but one eye-speck with one large ten- 

 tacle arising from the junction of each radiating tube with the circular tube; in Hip- 

 pocrene there are bunches of tentacles with eye-specks arising from the same position ; 

 while in Tiaropsis the tentacles are uniformly arranged all round the disk, without the 

 free spaces existing in both the former, in which the margins between the radiating 



