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POCILLO'PORA. A genus of stony 

 polypifers, thus named from the 

 pocilliform shape of the cells, from 

 which shape, as well as the margins 

 having little or no projection, this 

 genus is separated from madrepora. 

 Pocillopara is plant-formed, ramose 

 or lobated; the surface set with 

 deep cellules, with porous inter- 

 stices. There are several species, 

 found principally in the South sea 

 and Indian ocean. 



PODOPHTHA'LMIA. The first order of 

 the class Crustacea, comprising the 

 lobster, crab, crayfish, &c. 



PODOPHTHA'LMA. The name assigned 

 by Leach to a group of crustaceans 

 comprising the orders Decapoda and 

 Stomatopoda. The animals of this 

 group have their eyes supported on 

 moveable peduncles. 



POIKILITIC. (from 77-ot/aXos, Gr. va- 

 rious, variegated.) To the new 

 red sandstone group, M. Brongniart 

 has applied the name of Terrain 

 Pcecilien. Conybeare has proposed 

 to extend the term Pcecilitic to the 

 entire group of strata between the 

 coal formation and the lias, com- 

 prising the new red conglomerate, 

 the magnesian limestone, the varie- 

 gated sandstone, the shell limestone, 

 and the variegated marl. Some 

 common appellative, says Buckland, 

 for all these formations has been 

 long a desideratum in geology ; but 

 the word pcecititw is, in sound, so 

 like pisolite, that it may be better 

 to adhere more literally to the 

 Greek root, and apply the common 

 name of Poikilitic group to the 

 strata in question. 



POLAEIZED LIGHT. Light which by 

 reflection or refraction, at a certain 

 angle, or by refraction in certain 

 crystals, has acquired the property 

 of exhibiting opposite effects in 

 planes at right angles to each other. 



POLISHING SLATE. (Poherschiefer of 

 Werner.) A variety of tripoli. 

 Colour white, yellowish- white, or 

 yellow. Structure slaty. Cross- 



fracture dull and earthy. It is 

 very light, so as sometimes to swim 

 on water, strongly adheres to the 

 tongue, and is easily reduced to a 

 fine dry powder. Before the blow- 

 pipe it hardens, but does not fuse. 

 It principally occurs at Bilin, in 

 Bohemia, and is regarded as a 

 volcanic production. 



PO'LLEN. fpollen, Lat. fine flour.) 

 In botany, the fecundating powder 

 or dust contained in the anther. 

 In dry and warm weather the 

 anther bursts, and the pollen is 

 thrown out. 



POLTCH'(ETA. The first order of the 

 class annulata, comprising the 

 Nereis, serpula, and lob- worm. 



POLYGA'STKICA. (from TroXvs, many, 

 and <ya<nrjp, a stomach, Gr.) So 

 named from their possessing numer- 

 ous internal digestive cavities. The 

 lowest class of animals, belonging 

 to Diploneura, or Helminthoida. 



When we place, says Professor 

 Grant, a drop of any decayed infu- 

 sion of animal or vegetable matter 

 under a powerful microscope, and 

 throw a light through that drop, 

 and through the microscope to the 

 eye, we discover in the drop of 

 water various forms of living 

 beings ; some of a rounded, some 

 of a lengthened form, and some 

 exhibiting ramifications shooting 

 in all directions, but all apparently 

 of a soft, transparent, gelatinous, 

 and almost homogeneous texture. 

 In these minute animals there are 

 numerous cavities or stomachs, in 

 some of them being two hundred 

 in number. There is every reason 

 to believe that polygastrica exist 

 in every drop of water. They 

 form the food of other classes, more 

 especially the zoophytes. Almost 

 all the known genera of polygastric 

 animalcules possess eyes : they are 

 also found to possess an acute sense 

 of taste ; they distinguish, pursue, 

 and seize their prey, and, although 

 so excessively minute that five 



