NUTRITION IN MEDUSA. 77 



])etween this latter vessel and others, which per- 

 meate 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 commencement of a vascular 

 system, taking its rise from that cavity, and calcu- 

 lated to distribute the nutritious juices to every part 

 of the organization. 



There are other species of Medusae, composing 

 the genus Rhizostoma of Cuvier, which, instead of 

 having only one mouth, are provided with a great 

 number of tubes which serve that office, and which 

 bear a great analogy to the roots of a plant. f The 

 pedicle terminates below in a great number of 

 fringed processes, which, on examination, are found 

 to contain ramified tubes, with orifices opening at 

 the extremity of each process. In this singular 

 tribe of animals there is properly no mouth or cen- 

 tral orifice ; the only avenues to the stomach being 

 these elongated canals, which collect food from 

 every quarter where they extend, and which, uniting 

 into larger and larger trunks as they proceed 

 towards the body, form one central tube, or oeso- 

 phagus, terminating in the general cavity of the 

 stomach. The Medusa puhno, of which a figure was 

 given in vol. i., p. 175, belongs to this modern genus, 



* Journal de Physique, Ixxxix, 146. 



t It is from this circumstance that the genus has received the 

 name it now bears, and which is derived from two Greek words, sig- 

 nifying root- like mouths. 



