GENERAL CHARACTERS OP ACALEPHJE. 469 



the latter under the same general denomination, since they agree 

 in the peculiar character of the group as stated above, and cannot 

 be received into others. 



1027. The Acalephse derive their name (which means 

 nettles), from the stinging power which nearly all of them pos- 

 sess ; and some of their common names, as " Sea-nettles/' or 

 " Stang-fishes," have the same origin. This stinging power 

 appears due to a peculiar acrid secretion from the surface, which 

 remains after the death of the animal, and may be communicated 

 to substances which are placed in contact with it. They are 

 also commonly denominated "jelly-fish," " sea-blubber," &c. ; 

 partly from their uncouth appearance when cast upon the shore ; 

 and partly from the extreme softness of their tissues, which melt 

 away (as it were) when removed from the water. This delicacy 

 of structure is common to the whole group. In the greater 

 part, there is no hard support whatever; and the animals, 

 when taken out of water, lose their form completely. In a few 

 species, however, there is a very thin cartilaginous plate, which 

 retains its form when dry. The substance of these animals consists 

 of a tissue somewhat resembling cartilage (ANIM.PHYSIOL. 45); 

 but containing so little solid matter, that a Medusa, weighing 

 several pounds when alive, is reduced almost to as many grains 

 when dried. The fluid gradually drains away, leaving but a 

 thin pellicle incrusting the surface on which the mass was placed. 



1028. In most of all the Acalephse, which possess a distinctly 

 radiated form, the stomach or digestive cavity is central (Fig. 

 611). It usually opens by a single orifice, placed in the centre, 

 and surrounded by tentacula ; but there are several curious 

 species (Fig. 612), in which there is no regular mouth ; 

 the food being taken in by a number of suckers, having minute 

 orifices at their extremities. In all, however, it is remarkable, 

 that the number 4 and its multiples may be almost constantly 

 observed to govern the distribution of the organs. Although 

 possessed of a certain degree of locomotive power, the movements 

 of the Acalephse are very feeble ; they are carried about by the 

 ocean currents, almost at their mercy ; and many of them have 

 the means of making the gentle breezes subservient to their 



