NUTRITION IN MEDUSA. 85 



ment is extracted from this circulating fluid, and 

 made to contribute to the growth of these plant- 

 like structures, is entirely unknown. 



The apparatus for nutrition possessed by 

 animals belonging to the tribe of Medus(B is of 

 a peculiar kind. I have already described the 

 more ordinary form of these singular animals, 

 which resemble a mushroom, from the hemi- 

 spherical form of their bodies, and their central 

 foot-stalk, or pedicle. In the greater number 

 of species there exists, at the extremity of this 

 pedicle, a single aperture, which is the begin- 

 ning of a tube leading into a large central cavity 

 in the interior of the body, and which may there- 

 fore be regarded as the mouth of the animal ; 

 but in those species which have no pedicle, as 

 the JEquorea, the mouth is situated at the centre 

 of the under surface. The aperture is of suffi- 

 cient width to admit of the entrance of prey of 

 considerable size, as appears from the circum- 

 stance that fishes, of some inches in length, are 

 occasionally found entire in the stomachs of those 

 medusae which have a single mouth. The central 

 cavity, 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 almost be considered as consti- 



