302 



POLYPORUS 



POMACE.*; 



ment of many dry stony places in Scotland. 

 P. calaguala, a native of Pent, is said to possess 



Polypodiam : 



1, Polypoditim dryopterit ; 2, P. tmlyart. 



important medicinal properties solvent, deobstru- 

 ent, sudorific, &c. 



Polyporns. See AMADOU, and DRY ROT. 



Poly p'teriis, a genus of Ganoid fishes, of which 

 only one species (P. bichir) is known. It lives 

 in the Nile and western rivers of tropical Africa. 

 It may attain a length of 4 feet, and is esteemed 

 as food. Very characteristic is a series of dorsal 

 spines, with attached (inlet*, which extend almost 

 the entire length of the back. Of its life very 

 little is known. The only nearly allied living form 

 is Calamoicltthys calabarictts from Old Calabar. 



Polypus, in Surgery, is an ancient term em- 

 ployed to signify any sort of pedunculated tumour 

 attached to the surface of a mucous membrane, to 

 which it was supposed to adhere like a many- 

 footed animal, as its name indicates. The most 

 common seats of polypus are the nostrils and the 

 uterus ; but these tumours are also found in the 

 rectum, the larynx, and the external auditory 

 passage of the ear. The only satisfactory mode of 

 treatment consists in their removal, video must be 

 effected in various ways, according to their posi- 

 tion, as by the force]>s, ecraseur, ligature, &c. 



Polytcchniqne, or POLYTECHNIC SCHOOL 

 (Gr. finlyi, 'many,' techne, 'art'), is an institute 

 in which the technical sciences that rest in great 

 part upon a mathematical basis, such as engincer- 

 in;.', architecture, &c., are taught. The first school 

 <>f the kind was established in Paris ( 1794) by the 

 National Convention, under the name of School of 

 Public Works. No students were admitted but 

 those who intended to enter the public service, 

 especially the corps of civil and military engineers 

 and the artillery. The Polytechnic School, an it 

 was called from 1705, has lieen repeatedly reorgan- 

 ised as the diilcrcnt political parties have succeeded 

 to power. At the present time it is the institute 

 in which France trains her artillery and engineer 



officers, her naval engii rs, her directors of roads 



and bridges, and of mines, her telegraph ollicers, 

 in short, all her officials who require to know 

 something of the higher brunches of technical 

 "e. Herman} too has her polytechnics. Those 

 that came into licing during the first half of the 

 19th century were in great part training-schools 

 for the higher brunches of the industrial art* ; but 

 since Zurich established ilK-Vii a |xilyiechnie 



modelled on the plan of the German universities, 

 most of the German polytechnics have followed 

 suit. Of these establishments, thus increased in 

 seo|m (now called also 7V.7/ /./ /A/r/,W/ /), 



Germany has nin ten, and Austria-Hungary 



half a dozen; though Germany has also several 

 other colleges that might fairly claim the name of 

 I'ohjtii-liiiil.iiiii in the old sense. The nine techni- 

 cal colleges of Berlin. Hanover. Ai\-lu Cliapelle, 

 Munich, Dresden, Stuttgart, ('arlstuhe, Darmstadt, 

 and Branwick have some .V><> teachers and 0000 

 pupils the chief departments of instruction lieing. 

 architecture, civil engineering, machine making, 

 shipbuilding, cliemistiv. and metallurgy. In 

 America the oldest institutions of the kind are 

 the Rensselaer Polytechnic Institute, at Troy, 

 New York, and the Kninklin Institute, at Phila- 

 delphia, both founded in Is.'l. There are now 

 nearly a hundred technical schools in the United 

 States, more than half of them endowed with a 

 national land-grant. See TKI-IIMCAI. Km CATION ; 

 also ART; and Pinet, Histoire de I'lScole Poly- 

 technique (1886). 



Polytheism. See KKLIGION. 

 PolytrU'lllllll, a genus of Mosses (q.v.). 



Polyzoa, or HKYOZOA, a class of small animals 

 which, with one exception, form colonies, and are 

 almost always fixed. Most familiar are the SIM 

 mats or horn-wracks (Plofltra), cast -up pieces of 

 which are abundant on the beach. On these will be 

 seen the hundreds of separate chamliers in which 

 the minute individuals live. Kach individual has 

 a sac-like or cup-shaped body, traversed by a food- 

 canal lient like a U, crowned around the mouth 

 by a wreath of tentacles, controlled by a single 

 nerve-centre. The cuticle which surrounds the 

 body is usually horn-like, not (infrequently cak 

 ous (Cellepora, I.epralia, \-c. ), and sometimes 

 gelatinous (Alcyonidiiim, l.ophopns). The indi- 

 viduals of a colony are not always all nlike ; 

 thus, some of them are occasionally modified into 

 strange birds'-lteak-like or whip-like structmes. 

 All Polyzoa multiply by budding, and thus the 

 colonies increase. The individuals in the older 

 parts of the colony usually degenerate or die. 

 Fresh-water forms reproduce by peculiar winter 

 buds or slatohlasts, which are liberated on the 

 death of the parent, are floated away by currents, 

 and after a winter's quiescence develop in spring. 

 Hut all Polvzoa also reproduce sexually : the se\es 

 may be separate or united; the larva- developed 

 from the eggs are free swimming. The Polyzoa, 

 used to be ranked with zoophytes (among the 

 II \droxoa), but tin- individual animals are much 

 more complex and are independent of one another. 

 Often they are culled mollusi-oid, because of 

 apparent affinities with lamp-shells or lirachio- 

 |KM|S. which used to l>e regarded us allied to 

 molluscs. Most modern zoologists rank them as 

 a distinct but hetcrogeni-oiis class in the greVt 

 assemblage of 'worms' or 'Venues.' l!c|ircsctila- 

 live genera are Cristatella, l.ophopns, 1'luma 

 tella in fresh water: r'lustru, Memhranipora, 

 Alcyonidiiim, Cellepora marine : IVdiccllina and 

 LoMisoma two marine genera, simpler than the 

 others, the latter non-colonial. Hhabdnpleura, a 

 remarkable genus sometimes included in this class, 

 shows at least hint* of vertebrate atlim 



See Allmari. Krititk Freth-mitrr fnlyioa ( Lond. IS' 

 Husk, Challenger Report, X. (1884); Hinoks, riti*h 

 Marine Polyioa (Lond. 1880); & Kay Lankenter, article 

 ' Polyzoa ' in Kntp. Krit. 



Pomacea*, or POME*, according to some 

 botani-t-. a natural order of plants, but more 

 generally regarded as a sub order of Kosacen- (q. v. i. 

 The plants of this order are all trees or slmilis, 

 abundant in Kmopc, and cliiclK belong to the 



