MEDUSA. 



169 



below into the calmer regions^ where its delicate 

 organization is not exposed to the rude collision 

 of wave and wind. 



The beroe glides along by means of the ciliated 

 bands; but this is only one of the means of pro- 

 gression employed by the Acalephs. Some move 

 themselves about with cirrhi, and are therefore 

 called Cirrhigrade ; the beroe being called a cilio- 

 grade. Others again are named Physograde, 

 because they are buoyed up by a kind of bubble, 

 or bladder filled with air. The well-known Por- 

 tuguese Man-of-war is a good example of this 

 order. There is another order which moves 

 through the water by a series of regular pulsa- 

 tions like those of the lungs, and the species 

 belonging to it are called, in consequence, Pulmo- 

 nigrade. An example of a pulmonigrade Acaleph 

 is given in plate n, fig. 1. It belongs to the 

 genus -^gerea, of which many species may be 

 found on our coasts, and, with many others, 

 passes under the general title of Medusa. The 

 size of these creatures varies excessively, and 

 there are strange peculiarities in their growth 

 and structure, which should be learned from 

 some one of the books devoted exclusively to 

 the Acalephs. The movements of a little Medusa 

 in a clear glass vessel are exceedingly graceful, 



