SIMPLICIA. 651 



ating in the stomach, and proceeding by ramifications toward the circumference. Anoilier species, C. chrysaora, 

 has the margin furnished with long tentacula, and rows of brown or yellow spots, forming rays on the convex 

 surface. It is very common, and there are great varieties in the spots. 



Cuvier distinguishes under the name of 



Rhizostoma, — 

 Those Medusje which have no central opening or mouth, and which are thence supposed to draw their 

 nourishment by suction by the ramifications of tlie peduncle, or by the tentacula. They have four 

 ovaries or more. 



Rhizostoma, properly so called, have a central peduncle, more or less ramified according to the species. The 

 vessels which, arise in the small protuberances of the peduncle, unite in a cavity at its base ; and from this, other 

 vessels are ramified to all parts of the umbrella, or disc. The most common species is the blue Rhizostoma, which 

 is often left on sandy shores by the ebbing tide. The umbrella is sometimes two feet in diameter. The peduncle 

 is composed of four pairs of arms, which are very much branched and toothed, and each is furnished with two 

 auricles or appendages at the base, which are also toothed. A fine network of vessels, occupying the thickness of 

 the margin, extends all round the umbrella. According to the observations of MM. Audouin and Milne Edwards, 

 these Medusa; are social, or at least they are always met with in numerous shoals, swimming in the same direction, 

 and with the body obliquely inclined. 



The Cephece of Peron differ from the other Rhizostoma only by having filaments intromixed with the denta- 

 tions, or papilla; of the peduncle. The Cassiopeiiie have no peduncle ; and their arms, which are usually eight in 

 number, and sometimes branched, rise directly from the under surface. 



ASTOMA, — 



Might be the general name for those which have no central mouth, no ramifications of the peduncle, 

 and no cavities for the ovaries. 



Some, however, have the peduncle furnished on each side with filaments that may act as suckers. Others have 

 no filaments, but the extremity of the peduncle is hollowed out like a funnel, which seems to be the sucker, as 

 from it vessels ascend the peduncle, and others are ramified from its base all over the body. Others again, want 

 the funnel-shaped membrane, or it may have been mutilated before the specimens were obtained. There are still 

 others, which have no vestige of a peduncle ; but merely little suckers distributed over the under surface, on the 

 lines of the vessels which are ramified below it ; [and these suckers are, of course, so many little mouths]. Some 

 have no vestiges of suckers or any other external apparatus, but have both sides smooth ; and there are yet others 

 which have no trace even of internal vessels. The under surface of these is usually concave, and may act as a 

 stomach. These last are very simple animals, and difler from Hydra in scarcely anything but size. 



Beroe. 



This genus should be separated entirely from the Medusae. It has a globular body, provided witli 

 salient ribs, extending from the centre of the upper surface to that of the under, and bristled with 

 points or filaments, which appear to be connected with vessels in which there is some appearance of a 

 fluid circulating. The mouth is on the one extremity, and leads to a stomach, which occupies the axis 

 of the body. There are also on the sides two organs, which are probably analogous to what are con- 

 sidered the ovaries of the Medusae. 



B. pileus, a species very common in the Channel, has the body spherical, with eight ribs, and two ciliated 

 tentacula, which become very long by prejection of their inferior extremities. MM. Audouin and Milne Edwards 

 have described its natural organization with considerable minuteness, and have traced various sets of vessels, 

 but without being able very clearly to explain their functions. This species is understood to constitute great part 

 of the food of the common Whale. Naturalists have referred to the same genus very simple species, which consist 

 of only a sac, furnished with ciliae, and open at both ends. The Doliolum of Otto have not even projecting ribs, 

 but resemble barrels without bottoms. 



Callianira of Peron, differ from Beroe only in having the ribs more salient, and united two and two, so as to 

 form two sets of a sort of wings. Janira, resemble the last; but they have upon each side three long ciliated 

 ribs, and two filaments. Alcinaca, have a cylindrical body, open at the one end, and two large wings at the other, 

 which when folded up completely cover the body. The cylindrical part is marked with four salient ribs, which 

 end in points, and have eight braces of cilias. Ocyraca, have similar wings ; but they have no ribs, and only 

 four rows of ciliae on the cylindrical portion. 



Cestum, — 

 Bears, perhaps, the nearest resemblance to Beroe than to any other genus. It is a very long gelatinous 

 ribbon, having one of the sides furnished with two rows of cihas, and there are fainter traces of tlie same 

 on the other side: the mouth is in the middle of tlie inferior edge, and the stomach is embodied in the 

 gelatinous substance of the ribbon; from the anal extremity there proceed vessels which ramify toward 

 both extremities of the ribbon -, and near the sides of the mouth there are two vessels which are pro- 



