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POLYHA'LLITE. A mineral found at Ischel, 

 in Austria. It occurs in masses of a 

 fibrous texture. Lustre pearly. Specific 

 gravity 2 '76. 



POLYHE'DRON. (from TroXvc, many, and 

 (Spa, side, Gr.) A solid contained under 

 many planes or sides. 



POLYHE'DRAL. } Having many sides or 



POLYHE'DROUS. $ planes. 



POLYMI'GNITE. (from TTO\VG, many, and 

 fjiiyvv/jLi, to mix, Gr.) A newly disco- 

 vered mineral, which has been thus named 

 in consequence of the variety of its con- 

 stituent parts. It consists of titanic 

 acid, zirconia, lime, yttria, the oxides 

 of iron, cerium, and manganese, with 

 minute portions of magnesia, potash, 

 silica, and oxide of tin. It is of a black 

 colour ; crystallized in small prisms ; 

 scratches glass ; specific gravity 4 '8. 

 Fracture conchoidal. Lustre almost me- 

 tallic. 



PO'LYPE. The name given to each tube, 

 surrounded with its tentacula, of the 

 Polypus ; Polypus designating the entire 

 animal mass, composed of an aggregation 

 of Polypes. 



POLYPA'RIA. ) The fourth class of Radiata 



PO'LYPI. $ or Zoophytes ; thus named 

 from a supposed resemblance to an Oc- 

 topus, called Polypus by the ancients, 

 this resemblance arising from the ar- 

 rangement of the tentacula around the 

 mouth. 



These animals are commonly known 

 as Corals. From an idea which long 

 prevailed that these animals are allied to 

 marine plants, they obtained the name of 

 Zoophytes. The body is cylindrical or 

 conical, sometimes possessing no viscus 

 but its cavity ; at others possessing a 

 stomach, which is visible, and other or- 

 gans. The greater number of Polyparia 

 are inhabitants of the ocean, and from 

 the ocean's depths they raise those im- 

 mense reefs that at some future period 

 may form a communication between the 

 inhabitants of the temperate zones. Al- 

 though Polypi abound in every part of 

 the ocean, still it is in the warmer re- 

 gions that they grow in greatest luxuri- 

 ance. The tentacula of Polypi are ex- 

 quisitely sensible, and are frequently 

 seen, either singly or altogether, bending 

 their extremities towards the mouth 

 when any minute floating body comes in 

 contact with them. A question arises, 

 says Dr. Roget, with regard to the con- 

 stitution of these Zoophytes, similar to 

 that which has been proposed with regard 

 to trees, namely, what limit should be 

 assigned to their individuality ? Is the 

 whole mass, which appears to grow from 

 one root, and which consists of multi- 

 tudes of branches, proceeding from a 



common stem, to be considered as one 

 individual animal, or is it an assemblage, 

 or aggregation of smaller individuals ; 

 each individual being characterized by 

 having a single mouth, with its accom- 

 panying tentacula, and yet the whole 

 being animated by a common principle 

 of life and growth ? The greater number 

 of naturalists have adopted this latter 

 view, regarding each portion as provided 

 with a distinct circle of tentacula, as a 

 separate animal, associated with its neigh- 

 bours in the construction of a common 

 habitation, and contributing its quota to 

 the general nourishment of this animal 

 republic. 



POLYPI'FERA. ) That class of animals com- 



POLYPI'PHERA. $ monly known by the 

 name of Zoophytes. They are carni- 

 vorous, feeding upon living animalcules. 

 These animals precipitate immense quan- 

 tities of carbonate of lime, especially in 

 tropical seas. 



POLYPI'FEROUS. Animals which have po- 

 lypi ; zoophytes. 



POLYPE'TALOUS. (from 7ro\tf, many, and 

 TTtTaXov, a leaf of the corolla, Gr.) In 

 botany, a term applied to a corolla which 

 has the petals separate. 



POLYSE'PALOUS. (from TroXic, many, and 

 sepal, the name given to the parts of 

 which the calyx is composed.) In bo- 

 tany, a term given to a calyx which has 

 its sepals separate from each other. 



POLYPOTHE'CIA. A genus of spongeous 

 zoophytes found in flints. Miss Bennett, 

 in her catalogue of the organic remains of 

 Wiltshire, has described seven species. 



POLY'PTERUS. A genus of fishes found in 

 the Nile and in the rivers of Senegal. 

 M. Agassiz has described two species. 

 The Polypterus and Lepidosteus are the 

 only known genera of living representa- 

 tives of the sauroid fishes. 



POLYSPE'RMOUS. (from TTO\UC, many, and 

 GirkpfjLa, seed, Gr.) In botany, a term 

 applied to the ovarium and fruit when 

 they contain many seeds. 



POLYTHA'LAMOUS. (from TroXvg, many, and 

 OaXanoQ, a chamber, Gr. ) Having many 

 cells or chambers, as potythalamous 

 shells ; multilocular ; camerated. 



PORCELANA'CEOUS. > Resembling porce- 



PORCELA'NEOUS. $ lain. Shells have 

 been divided into two classes. The first 

 are of a compact texture, have an ena- 

 melled surface, and are generally beauti- 

 fully variegated. The shells of this class 

 have been termed porcelanaceous, or por- 

 celaneous shells ; they contain but a 

 small proportion of soft animal matter. 



PORCE'LLANITE. A mineral of various co- 

 lours, from grey to nearly black, occur- 

 ring in amorphous masses or fragments, 

 which are often rifted. Porcellanite 



