NUTRITION IN MEDUSA. 81 



be considered as so many mouths : and all termi- 

 nating above, in a common receptacle or intestine. 



Many gradations are observable in the com- 

 plexity of the digestive cavities of this extensive 

 tribe, for while some, as the Eudora, have, to all 

 appearance, no internal cavity corresponding to a 

 stomach, and are totally unprovided v^^ith either 

 pedicle, arms, or tentacula ; others, furnished with 

 these latter appendages, are equally destitute 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, apparently 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 nu- 

 merous, as we have seen in the Rhizostoma.* In 

 the Beroe, the alimentary tube is no longer a 

 closed sac, but terminates in an external orifice. 

 It is difficult to conceive in what mode nutrition is 

 performed in the agastric tribes, or those destitute 

 of any visible stomach ; unless we suppose that 

 their nourishment is imbibed by direct absorption 

 from the surface. 



Ever since the discovery of the animalcula of 

 infusions, naturalists have been extremely desirous 



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

 VOL. II. G 



