4 NUTRITIVE SYSTEM. 



lips. To these there is superadded, in the genus Turris, longitudinal^ highly-developed muscular 

 bandsj 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 Medusae 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 obepng 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 Discophora 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 piade 

 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 Discophorse, 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 Mquorea, where it is almost an open space surrounded by a slight 

 veil of membrane. In Turris and-Oceania, it is also large and well defined. In WiUsia and 

 Thaumantias, it is campanulate, and occupies the greater part of the peduncle. In Geryonia 

 and Tima, it is small, in comparison with the peduncle, and confined to its extremity. 

 In Slabheria, Sarsia, and Steenstrupia, it is tubular, but can assume a bell-shape. In 

 Bougainvillea and Li%%ia,\t 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 Thaumantias 

 leucostyla, he found a distinct cavity separated from the stomach at its base, the walls of 



