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ACALEPHA. 



THE TH[RD CLASS OF THE KADIATA — 



THE ACALEPHA,— 



Includes all tliose Radiated Animals which swim in the waters of the ocean; and in 

 which we can still perceive vessels, though these vessels arc, in truth, little else than 

 intestinal tubes, ramified through the parenchyma of the body. They admit of a natural 

 division into two orders, — Simple and Hydrostatic. 



THE FIRST ORDER OF THE ACALEPHA. 



THE ACALEPHA ^IMPLICIA. 



These float and swim in the water, by alternate contractions and dilatations of the Ijody, 

 although their substance is merely gelatinous, and without any apparent fibres. The ap])areut 

 vessels fonml in some of them are only hollows in the gelatinous substance originating from the 

 e.tomach, and offering no proof of a true circulation. There ai'e obvious points of resembUmce 

 among tiK-m all ; but still they admit of division into genera and subgenera. 



Medusa, — 

 Have a ccnti al ili:.e, moro or less convex, on the upper surface, something like the bead of a mushroom, 

 am] termed the umbrella. The contractions and dilatations of this disc con- 

 tiihiite to the locumution of the animal ; [but they are not powerful enough for 

 stemming ra})t(l currents of the water.] The margins of the uinbrella, and those 

 of the mouth, or of the suckers which supply the place of a mouth, in the miildle 

 of the under snrface of the disc, are furnished A\itli tentacula, very much v;u-ied 

 in form and size, and these variations are the basis of many subdivisions of the 

 genus. [They are very numerous ; and the small ones give the seas in which they 

 aViound the appearance of being crowded with flakes of half-mcked snow. Some 

 of theac :^ho\v tine priimatic colours ; and in not a few the gelatinous matter which Alls the integument 

 of the djbc is of so aeriil a nature as to irritate and blister the skin, even after it has been dried.] 



Mi'dasa, properly so called, includes all those that have a true month on tlic mid(.-r side of the disc ; but this 

 mouth is sometimes a simple opening'', and at other times placed on a peduncle. 



.-Jiquorea, includes those in which the mouth is simple, and not on a peduncle, or furnished with arms or ten- 

 tacula. When there are no tentacula round the disc, they form the Phorcynia of Lamarck. When the disc is 

 furnished with tentacula all rnnnd, they are the .'E'/norra strictly so railed, and one of the most numerous in the 

 warm seas. Some have the undi.T surface covered ■\vitli laminre, and others liave the margins of the umbrella 

 diversified by furrows. 



Pclag'ia, comprehends those which have the mantle produced into a peduncle, or divided iutu arms or ten- 

 tacula. 



in all these subgenera, there are no lateral cavities ; but in the majority of those with a simple mouth, there are, 

 in riie substance of the umbrella, four organ.s inclosed in furrowed membranes, which, at certain seasons of the 

 year, are tinged with a dark-coloured substance, understood to be the germs of the young. They are lodged in four 

 cavities, which ojten near the mouth, or the sides of the peduncle ; and as small animals are sometimes entangled 

 in them, some have regarded tliem as mouths, and others as organs of respiration. That they are not mouths is 

 evident, and the respiration appears to be performed by the margin of the umbrella. The tentacula, whether on 

 the margin of the umbrella, or round the mouth of the animal, vary not only in ditTereut species, but in the 

 ditlcrent agi.'S of (he same species. 



CVAXEA,— 



Includes all tlic species whieb have a central mouth, and four lateral ovaries. 



C. ai'i-ifo, is oni' of the most common and wirlely distributed species. With age, it acquires four very long 

 arms : tliL: murgiu of tl)e umbrrlla :.- finely ciliated all round ; and within it are observed reddish vessels origin- 



