POLYHYMNIA. 219 POLYNESIANS. POLYHYMNIA, or POLYMNIA (Lat.,from Gk. HoXuf/jLvia or UoXvfina). One of the nine Pluses (q.v.). lien in late times the functions of the pluses were specialized, she became the iluse of tlie pantomime, and was represented without special .attribute, but closely wrapped in her mantle, and sometimes with her hand upon her mouth. POLYMASTODON (Xeo-Lat., from Gk, iroKvs. iK'lyi. nuioli. many + /locrros, niastos, breast, -- ooot/i, odous, tooth ) . A fossil multi-tuber- culate animal of the size of a beaver, of which fiagmentary remains have been found in the basal Eocene or Puereo beds of Xew Mexico. The jaws and dentition have some resemblances to those of rodents. POLYMORPHISM (from Gk. mXtis, polys, much, many + ii.op(prj. morphe. form). The differ- entiation either of one animal into two or more incomplete undetached individuals ( pseudindivid- uals) or zoiiids, as in the Siphonophores or Phy- salia; or that of the animal into two separate sexes, or of the latter into castes, as in the termites and ants. Instead of the functions of the whole animal or plant being equally distributed to the individual organs, some of the organs or parts of the animal are set apart for this or that function. In the hydra the individual is nionomorphic, not divided into male and female individuals, but in Hydractinia, a fixed, vegetative form, there arise sexual or reproductive zoiiids, some female and others male, and also hydra-like or nutritive zoiiids or incomplete individuals. In the Por- tuguese man-of-war Iq.v. ) we have a still better example of incomplete polymorphism. Thus, as Hertwig states, division of labor leads to greater centralization, "the more polvmorphic an animal colony becomes, the more unified it is, the more it gives the impression of being a single animal instead of an aggregation of single animals." In the hydroids alternation of generations (q.v.) has arisen from a division of labor or polymorphism of individuals originalh- of equiv- alent value, in which some individuals (the sex- ual ones) have separated and acquired a pecu- liar structure. Moreover, while alternation of generations has arisen from polymorphism, it can again produce it. Hertwig illustrates this by the case of certain medusae, which, instead of sepa- rating, remain permanently attached to the col- ony. The}' then degenerate into 'sporosacs,' in which a mouth, tentacles, and a velum are wanting. A second kind of polymorphism is that seen in the males and the females of most animals. This is sexual dimorphism, which may pass into sex- ual polymorphism. This is complete polymor- phism. Reproduction by budding involves the differentiation of the animal form into three kinds of individuals — i.e. males, females, and 'neuters.' as among insects. Among the coelente- rates and worms the forms reproducing by par- thenogenesis (q.v.) are usually larval or imma- ture, as if they were prematurely hurried into existence, and their reproductive organs had been elaborated in advance of other systems or organs, for the sudden production, so to speak, of large numbers of individimls like themselves. Among insects dimorphism is intimately con- nected with organic rejiroduction. Thus the sum- mer wingless asextial aphis and the perfect winged autumnal aphis may be called 'dimor- ToL. :xvi._i3. phic' forms. The perfect female may assume two forms, so much so as to Ije mistaken for two distinct .species. Dimorphism i>- Bibds. Besides ordinary sex- ual dimorphism, depending on sex. and comprised under the head of secondary se.xual characters ( .see Sex ; Sexual Selection ) , a few special eases are known, due probably to climate or local causes. Thus, in some species of skua, a parti- colored bird may frequently be found mated with a unicolorous form, either male or female. In the guillemots at nearly every breeding station about one in twenty may be marked with a white circle around the eye, and a white line extending backward from it. these ringed or bridled guillemots being of either sex and apparently paired with birds of normal plumage, no inter- mediate forms being known. (See Dichboma- TISM IX Bibds.) A striking example of dimorph- ism in respect to the beak is furnished by "the huia ( q.v. ) . DiMOBPHISM AXD POLYMOBPHI.SM IX IXSECTS. Although sexual dimorphism is very prevalent in insects, there are many instances of dimorphism, resulting from local causes, as temperature. ( See Temperatuee Vabieties, especially as relating to seasonal dimorphism, wet and diy forms.) Certain species of grasshoppers are dimorphic. In the honey-ant { ilyrmecocystus Mrxicantis), besides the usual workers, there occur individuals with enormous spherical abdomens tilled with honey. Here the cause is evidently connected with the food. See, for other examples, EvoLU- TIOX. paragraph Polymorphism. The chief initial or determining causes of di- morphism and polymorphism, besides sexual selection (q.v.). are changes in temperature, of light, and of other physical agents. POLYMORPHOUS (in geology). See Iso- morphism. POL'YNE'SIA (Xeo-Lat., from Gk. ■-oHc, polys, much, many -(- w/crof, jic.sos, island). A name once applied to all the islands in the Pa- cific Ocean, l.ving between Asia and America. By modern geographers the name is used to desig- nate a division of Oceanica comprising all the islands not included under Micronesia or Melo- nesia. The most important of them are the Tonga, Samoan, Ellice, Cook. Society. Hawaiian, and ilarquesas Islands, and Low Archipelago. The Fiji Islands are included by some in Pol- ynesia and by others in Melanesia, all of which are described in separate articles. For a descrip- tion of the inhabitants of these islands, consult: Stevenson. In the South Seas (Xew York. 1896) ; Becke, Wild Life in Southern Seas (London, 1897) ; Mager, Le monde polynesien (Paris, 190-2). See Poltxesiaxs. POLYNESIANS. A term used diversely by various writers. By some it is employed as a synonvm of Malayo-Polynesian (q.v.) and made to include all the so-called brown race of the re- gions known as Malaysia, ilicronesia. Melanesia, and Polynesia, also known as the Malayan race. F. Miiller (1879) made the Poly-ilclanesians one of the branches of his ilalay race, while Brinton (1890) divides his ilalayic stock into a Western (Malayan) and an Eastern (Polyne- sian) group. Deniker makes the Pnlvnesians properly so called one of the great ethnic groups of the Indo-Pacific area. Keane (1896) holds that the Eastern Polynesians are a branch of
