NUTRITION IN MEDVSM. 9t 



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 ob- 

 served in the complexity of the digestive cavities 

 and other organs, of the various species of this 

 extensive tribe, is exceedingly remarkable : for 

 while some, as the Eudora, have, to all appear- 

 ance, no internal cavity corresponding to a sto- 

 mach, and are totally unprovided with either 

 pedicle, arms, or tentacula ; others, furnished 

 with these latter appendages, are equally desti- 

 tute of such a cavity ; and those belonging to 

 a third family possess a kind of pouch, or false 

 stomach, at the upper part of the pedicle, appa- 

 rently formed by the mere folding in of the 

 integument. This is the case with the Geronia^ 

 depicted in Fig. 250, whose structure, in this 

 respect, approaches that of the Hydra, already 

 described, where the stomach consists of an 

 open sac, apparently formed by the integuments 

 alone. Thence a regular progression may be 

 followed, through various species, in which the 

 aperture of this pouch is more and more com- 

 pletely closed, and where the tube which enters 

 it branches out into ramifications more or less 

 numerous, as we have seen in the Rhizostoma.* 

 It is difficult to conceive in what mode nutrition 



* See Peron, Annales du Museum, xiv. 330. 



