68 



ACALEPH.E. 



the whole apparatus gives not a very bad representation of the 

 paddle-wheel of a steam-boat. The cause of their movements is 

 however as little evident in the Beroeform acalephte as in the 

 minute Polygastrica. Under the arches which support them 

 are vessels containing a fluid, which Dr. Grant imagines may in 

 some manner be injected into the tubular structure, and thus cause 

 them to become erected ; but how their rapid motions are excited, 

 is still far from being explicable. 



But one of the most beautiful examples of a ciliated medusa 

 is seen in the Girdle of Venus (Cesium Veneris) (fig. 23). 



Fig.23. 



This creature is a long, flat, gelatinous riband, the margins of 

 which are fringed with innumerable cilia, tinted with the most 

 lovely iridescent colours during the day, and emitting in the dark 

 a phosphorescent light of great brilliancy : in this animal too, 

 which sometimes attains the length of five or six feet, canals may 

 be traced running beneath each of the ciliated margins, analogous 

 to those which exist in the Beroe, and no doubt answering a 

 similar purpose. 



(96.) Physograda. In the third division of acalephae, de- 

 nominated by Cuvier " Acalephes Hydrostatiques," the body is 

 supported in the water by a very peculiar organ, or set of organs, 

 provided for the purpose. This consists of one or more bladders, 

 capable of being filled with air at the will of the animal, which 

 are appended to the body in various positions, so as to form floats 

 of sufficient buoyancy to sustain the creature upon the surface of 

 the sea when in a state of distension ; but, when partially empty, 

 allowing it to sink, and thus escape the approach of danger. In 



