OF THE MARGINAL CORPUSCLES. 
417 
towards the ventral surface of the disc ; the under margins of the fissure in which it 
is lodged are prolonged into two overlapping fringes. The cavity of the pedicle is 
continuous with that of a canal which runs from the common cavity directly towards 
the corpuscle. Its walls are continuous, the inner with the inner wall of the canal, 
the outer with the substance of the disc. The pedicle is in fact a mere process of the 
system of canals, so that the position of the marginal vesicle is relatively to this 
system the same as in the Cryptocarpse. A similar remark holds good with regard 
to the Rhizostomidee. 
22. In Cephea and Rhizostoma the organ is placed in a notch between two lobe- 
like processes of the margin of the disc, and looks upwards. On the upper surface a 
semilunar fold extends from one lobe to the other and covers in the corpuscle ; below, 
the edges of the lobes are thinned and overlap, figs. 33, 34. 
23. There are some peculiarities in Rhizostoma which deserve to be noticed more 
fully. On the dorsal surface, behind the semilunar fold above mentioned, there is a 
large heart-shaped depression (fig. 33) with its base towards the corpuscle. Its sur- 
face is thrown into prominent arborescent folds, and is very richly ciliated. The 
deepest part of the depression is towards its base, and seems to take the direction of 
the base of the pedicle of the marginal corpuscle, which is just below it. I could 
not pass a needle from the depression into the cavity of the pedicle, but I have no 
doubt that they communicate, as on a lateral view the deepest part of the depression 
seems to project into the cavity of the pedicle. Furthermore, on pressure, the 
granules usually contained in the cavity of the pedicle sometimes passed into the 
depression. 
24. Ehrenberg describes apertures in Medusa aurita by which the system of 
canals communicates with the exterior, but they are alternate with the marginal 
corpuscles, not under or above them. In Cephea Wagneri, again, according to Will, 
the canals open beneath the marginal vesicles. I did not observe this in the Cephea 
ocellata. 
25 . On the ventral surface a much slighter semilunar fold connects the base of 
the two lobes, fig. 34. In the centre, behind this, there is an elevation of the sub- 
stance of the disc, to which the muscular bands which run along the under surface 
of the disc converge. 
26. The canal which runs to the marginal vesicle gives oft’ branches on each 
side, then opposite the base of the vesicle forms a dilatation rather larger than the 
cordate depression ; from this a csecal process passes off into each lobe, and so ter- 
minates. The termination of the canal in Cephea and Phacellophora is similar, but 
in the latter the caeca gives off lateral anastomosing branches, fig. 25. 
27 . In Rhizostoma the pedicle is somewhat bent and enlarged at its upper half. 
The inner membrane is richly ciliated, and the cavity which it incloses usually con- 
tains a number of rounded cell-like bodies floating about in incessant motion. There 
is a considerable space between the inner and outer membranes, which are thick, and 
