24.6 THE MICROSCOPE. 



AOALEPHjE. 



In great variety of form and colour, swimming freely about the waters 

 of the ocean, are found in abundance the beautiful Acalephse. From 

 some of them having a remarkable stinging property, they have derived 

 their name of Sea-nettks, while others, from their gelatinous nature, are 

 commonly called Sea-jelly, or Jdly-fish; one of which is shown in the 

 title-page of this work, depending from the top. 



These interesting animals were first arranged in three orders: A. 

 stabiles (fixed), A. liberce (free), and A. hydrostaticcB (hydrostatic). 

 Cuvier classed. them in two orders : A. simplices, and A. hydrosiaticcB. 

 They are now, however, divided into four orders, and classed in groups 

 according to the peculiar mode in which they effect their locomotion. 



The Medusce, spread on the surface of the water, a beautiful jelly- 

 like mass, that in form resembles an umbrella ; and by a continual con- 

 traction and opening out of this part, they pass along in the path they 

 desire. They are all more or less phosphorescent. The Beroe, like 

 many of the Infusoria, propel themselves with active ciliated arms. (See 

 fig. 1 15.) The Physalidce have an organ common to fishes, — swimming 

 bladders, — by filling or emptying which they rise or sink, and move 

 along in their watery home. 



The Portuguese Men-of-war have a large bladder, which, when 

 filled with air, rises above the surface of the waves, and is propelled by 

 the wind; a contrivance something similar to, though more successful, 

 we suspect, than the proposition to drag along land-carriages by means 

 of balloons. 



The flat circular horny disk forming the skeleton oi Propita gigantea, 

 to the naked eye exhibits both radiating and concentric markings ; and 

 when examined with a power of 40 diameters, its upper surface is found 

 to be furrowed, and two rows of small projecting spines occur upon the 

 ridges between the furrows, the ridges being the radiating fibres above 

 noticed. The under-surface, or that to which the greater portion of the 

 soft parts of the animal are attached, is more deeply furrowed; andplicre 

 or folds of the mantle fit accurately into the furrows, from which they 

 can easily be removed by the application of a gentle force. The con- 

 centric markings have in all cases small scalloped edges ; they occur at 

 certain regular intervals, and are so many indications of the lines of 

 growth. In the centre there is a circular depression ; and between its 

 aircumference and that of the first concentric marking, there are eight 

 flattened radii. If the under-surface be examined with a power of 100 

 linear, the ridges will all be found to have small jointed tubular pro- 



