480 ACALEPHA. 



MEDUSA, Linnteus. 



The Medusa- are furnished superiorly with a disk more or less convex, 

 resembling the head of a mushroom, and called the umbella. Its contractions 

 and dilatations assist the locomotion of the animal. The edges of this 

 umbella, as well as the mouth, or the suckers more or less prolonged 

 into pedicles which supply the want of it, in the middle of the inferior 

 surface, are furnished with tentacula of various forms and very different 

 sizes. These various degrees of complication have given rise to numerous 

 divisions. 



We will designate by the general name of 



MEDUSA, 



Or Medusa proper, those which have a true mouth in the middle of the infe- 

 rior surface, either simply open at the surface or prolonged into a pedicle. 

 Under the name of 



We may reunite those in which this mouth is simple and not prolonged, nor 

 furnished with arms. 



When there are no tentacula round the umbella they constitute the PHOR- 

 CYNIA of Lamarck. 



When the circumference of the umbella is furnished with tentacula, we 

 have the JEQUOREA proper JEQUOREA of Peron one of the most numerous 

 of all the subgenera, particularly in the seas of hot climates. 



Certain species are remarkable for having their inferior surface covered with 

 lamina 1 , and others FOVEOLIA, Peron for little fossulx 1 , which are placed 

 round the circumference of the umbella. 



We might also unite under the name of 



PELAGIA, 



Those in which the mouth is prolonged into a peduncle, or is divided into 

 arms. 



In all these subgenera there are no lateral cavities, but in a much greater 

 number of these Medusae with a simple mouth, we find, in the thickness of 

 the umbella, four organs formed of a plaited membrane, which at certain 

 seasons are filled with an opaque substance, and which appear to be ovaries. 

 They are usually placed in as many cavities opening on the inferior surface, 

 or on the sides of the pedicle, and which have been erroneously (in my 

 opinion) taken for mouths, because little animals are sometimes entangled in 

 them. Others consider them as organs of respiration, but that function is 

 most probably exercised by the edges of the umbella. The tentacula, whether 

 situated on the margin of the umbella or round the mouth, vary, not only 

 according to the species, but to the age of the animal. 



We will unite, under the name of 



CYANEJE, Cuvier, 

 All the Medusae with a central mouth and four lateral ovaries. 



