MEDUSA. 



175 



^ 5. Acalephce. 



Floating masses of living gelatinous matter are 

 met with in every part of the ocean ; often in vast 

 numbers, and of various forms; and having but 

 little the appearance of belonging to the animal 

 kingdom. They compose the order Acalephce, of 



which the Medusa (Fig. 

 81) may be taken as the 

 type. They appear, from 

 their organization, to be 

 raised but a single step 

 above polypi ; and in point 

 of activity and locomotive 

 powers, they rank among 

 the lowest of those Zoo- 

 phytes which are not per- 

 manently fixed to the spot 

 where they were first de- 

 veloped. They are almost wholly passive beings, 

 floating on the surface of the sea, or remaining at a 

 small depth below it, carried to and fro by the 

 motion of every tide and current, and destined to 

 be the unresisting prey of innumerable tribes of 

 animals which people every part of the ocean. 



The usual form of a Medusa is that of a hemis- 

 phere, with a marginal membrane, like the fold of 

 a mantle, extending loosely downwards from the 

 circumference ; together with a central pedicle 

 descending from the lower surface, like the stalk of 

 a mushroom, and terminating below in several 

 fringed laminae, or processes, which have sometimes 

 been denominated tentacula. 



