66 THE VITAL FUNCTIONS. 



width to admit of the entrance of prey of considerable size, 

 as appears from the circumstance that fishes of some inches 

 in length are occasionally found entire in the stomachs of 

 those medusae which have a single mouth. The central ca- 

 vity, which is the stomach of the animal, does not appear to 

 possess any proper coats, but to be simply scooped out of 

 the soft structure of the body. Its form -varies in different 

 species; having generally, however, more or less of a star- 

 like shape, composed of four curved rays, which might al- 

 most be considered as constituting four stomachs, joined at 

 a common centre. Such, indeed, is the actual structure in 

 the Medusa auinla, in which Gaede found the stomach to 

 consist of four spherical sacs, completely separated by par- 

 titions. These arched cavities, or sacs, taper as they radiate 

 towards the circumference, and are continued into a canal, 

 from which a great number of other canals proceed, general- 

 ly, at first, by successive bifurcations of the larger trunks, 

 but afterwards branching off more irregularly, and again 

 uniting by lateral communications so as to compose a com- 

 plicated net-work of vessels. These ramifications at length 

 unite to form an annular vessel, which encircles the margin 

 of the disk. It appears, also, from the observations of Gaede, 

 that a farther communication is established between this lat- 

 ter vessel, and others which permeate the slender filaments, 

 or tentacula, that hang like a fringe all round the edge of 

 the disk, and which, in the living animal, are in perpetual 

 motion. It is supposed that the elongations and contractions 

 of these filaments are effected by the injection or recession 

 of the fluids contained in those vessels.* Here, then, we 

 see not only a more complex stomach, but also the com- 

 mencement of a vascular system, taking its rise from that 

 cavity, and calculated to distribute the nutritious juices to 

 ' every part of the organization. 



There are other species of Medusae, composing the ge- 

 nus Rhizostoma of Cuvier, which, instead of having only 



* Journal dc Physique, Ixxxix. 146. 



