4 NUTRITIVE SYSTEM. 
lips. To these there is superadded, in the genus 7urris, longitudinal, highly-developed muscular 
bands, running from the base of the peduncle to the marginal band. Whatever be the 
arrangement, the movement is the same. The animal swims in an oblique position, con- 
tracting and expanding alternately its umbrella; occasionally pausing as if to rest, but capable 
of continuing its motions for an indefinite time. The lips can be expanded or contracted as 
occasion may require to seize its prey. The tentacles in many species are capable of wonderful 
extension, and can be retracted suddenly into a very small compass, often into a mere tubercle ; 
but there are many naked-eyed Medusz which vary their tentacles at an almost uniform 
length. Each of these organs may be extended or contracted singly, or in concert with its 
fellows, evidently obeying promptly the will of the animal of which they form part. They 
guide the Medusa through the sea, and can anchor it. I have seen a Geryonia anchor itself 
by means of its lips, clasping a coralline with them, and remaining tranquil so fixed for a 
considerable time. 
Nutritive System.—This consists of a stomachal cavity; excavated in a more or less 
produced proboscis, depending from the summit of the sub-umbrella, opening externally by a 
more or less expanded mouth, margined by variously-formed contractile lips, and superiorly 
communicating with a system of radiating canals, which run to a common marginal canal. 
The orifices of these canals probably in every case open into a common cavity or intestinal 
reservoir superior to the stomach, though sometimes stated to open directly into the latter. 
The true position of the stomach in these animals has been a subject of much dispute, which 
is not to be wondered at, considering the extreme variations presented by the central peduncle. 
It was indeed for a long time supposed that several of the Discophore had no true mouths, 
but absorbed, as if by suckers or roots, their nourishment from without, a view, however, 
which all the more recent researches have tended to disprove. By some naturalists, the 
cavity above the cavity of the peduncle has been regarded as the stomach, and the latter as a 
pharynx, a view which has been partially supported by Milne Edwards. Eschscholtz made 
the mistake of supposing the ovaries in the naked-eyed species to be stomachs. Will, and 
more recently Frey and Leuckhart, regard the peduncular cavity only as the stomach, a view 
which, certainly among the gymnopthalmatous Discophoree, I hold from my own observations, 
for I have observed that the process of digestion goes on wholly in that cavity. Its dimen- 
sions vary greatly ; among our British forms, it is especially large in Stomobrachium, a genus 
which approaches nearly 4’quorea, where it is almost an open space surrounded by a slight 
veil of membrane. In Zurris and Oceania, it is also large and well defined. In Wallsia and 
Thaumantias, it is campanulate, and occupies the greater part of the peduncle. In Geryonia 
and Zima, it is small, in comparison with the peduncle, and confined to its extremity. 
In Slabberia, Sarsia, and Steenstrupia, it is tubular, but can assume a bell-shape. In 
Bougainvillea and Lizxia, it is a conical cavity, with singularly branched lips. The commu- 
nication of the stomach with the gastro-vascular canals is not clearly made out in all the 
genera. Will, in his description of Geryonia pellucida, states that at the fundus of the 
stomach there are four small obtuse prominences, each of which presents a small aperture, 
which is the orifice of one of the water-canals. In another species, the base of the stomach 
into which the vessels opened seemed to be separated from the remainder. In Zhaumantias 
leucostyla, he found a distinct cavity separated from the stomach at its base, the walls of 
