NUTRITION IN MEDUSAE. 69 



may be seen the canals, marked by the dark lines (c, c, c,) 

 which arise from numerous orifices in the extremities and 

 fringed surface of the tentacula, and which, gradually uniting 

 like the roots of a plant, converge towards the centre of the 

 pedicle, and terminate by a common tube, which may be 

 considered as the oesophagus (o,) in one large central cavity, 

 or stomach (s,) situated in the upper part of the cupola. The 

 section of this oesophagus is visible at the centre of Fig. 249, 

 where its cavity has the form of a cross. The stomach has 

 a quadrangular shape, as in the ordinary medusae, and from 

 each of its four corners there proceed vessels, which are con- 

 tinuous with its cavity, and are distributed by endless rami- 

 fications over the substance of the cupola, extending even to 

 the fringed margin, all round its circumference. The mode 

 of their distribution, and their numerous communications by 

 lateral vessels, forming a complete vascular net-work, is seen 

 in Fig. 251, which represents, on a larger scale, a portion of 

 the marginal part of the disk. The two large figures (249 

 and 252) also show the four lateral cavities (R, R, Fig. 252,) 

 which are contiguous to the stomach, but separated from it 

 by membranous partitions: these cavities have, by some, 

 been supposed to perform an office in the system of the Me- 

 dusa, corresponding to respiration; an opinion, however, 

 which is founded rather on analogy than on any direct ex- 

 perimental evidence. The entrances into these cavities are 

 seen open at E, in Fig. 249, and at E, E, in the section Fig. 

 252. A transverse section of one of the arms is given in 

 Fig. 253, showing the form of the absorbent tube in the 

 centre: and a similar section of the extremity of one of the 

 tentacula is seen in Fig. 254, in which, besides the central 

 tube, the cavities of some of the smaller branches (B, B,) 

 which are proceeding to join it, are also visible. 



The regular gradation which nature has observed in the 

 complexity of the digestive cavities and other organs, of the 

 various species of this extensive tribe, is exceedingly re- 

 markable: for while some, as the Eudora, have, to all ap- 

 pearance, no internal cavity corresponding to a stomach, and 



