RAP 



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REG 



1. The name given to animals which dart 

 upon and seize their prey. 



2. The name given to certain parts of 

 insects. The legs are called pedes ; when 

 adapted to the seizing of prey, they are 

 suitably called pedes raptorii, not arms. 

 The idea of arms presents a certain or- 

 ganization not found in insects, although 

 the raptorious legs of insects may possibly 

 be analogous in their functions. Shuck- 

 ard. 



RA'TIO. (ratio, from reor, Lat.) The 

 relation which one quantity bears to an- 

 other. 



RA'VIN. ) (ravin, Fr.) A deep, hollow, 



RA'VINE. 5 narrow excavation formed by 

 the force of running water. The French 

 use the two words ravin and ravine in 

 different significations. The word ravin, 

 a substantive masculine, is used to express 

 a place which has been hollowed out by 

 a stream of running water, as "passer un 

 ravin profond." Ravine is employed to 

 denote a torrent of water, " espece de 

 torrent forme d'eaux qui tombent subite- 

 ment et impetueusement des montagnes, 

 ou d'autres lieux eleves, apres quelque 

 grande pluie." Sometimes, however, 

 ravine is used also to signify the place 

 worn by the torrent. 



RAY. (from raja, Lat. raie, Fr.) A fish 

 of the sea. The rays form a genus of 

 fishes of the order Chondropterygii ; they 

 may be known by their flattened body, 

 which is in the form of a disk, from the 

 union of the body with the very broad 

 and fleshy pectorals, which are joined to 

 each other before or to the snout, and 

 which extend behind the two sides of the 

 abdomen as far as the base of the ventrals. 

 The rays have no ribs. The phalanges of 

 the carpus are very numerous, and each 

 is subdivided into several pieces by regu- 

 lar articulations ; they are arranged close 

 to one another in one plane, and form an 

 effectual base of support to the integu- 

 ment which covers them. Both the an- 

 terior and posterior extremities are sup- 

 ported by arches of bones, forming a sort 

 of belt. In this genus are included the 

 skate, torpedo, and sting-ray. The di- 

 rection of the eyes is oblique. Rays are 

 sometimes called sea-eagles, because, in 

 their rage and fury, they occasionally 

 raise themselves out of the water, and 

 fall again with such force as to make the 

 sea foam. Mr. Kirby, quoting from La- 

 cepede, says, an individual of a species of 

 this tribe, called by the sailors the sea- 

 devil, taken at Barbadoes, was so large, 

 as to require seven pairs of oxen to draw 

 it on shore ; he very judiciously, how- 

 ever, adds two notes of admiration to this 

 marvellous story. Fossil rays are abun- 

 dant throughout the tertiary formation ; 



they occur also in the Jurassic limestone ; 

 not any have been found in any stratum 

 older than the lias. 



RAYS OF FISHES. A name given to the 

 fins of certain fishes. Dr. Roget says, 

 the dorsal fins are supported by a series 

 of slender bones which are joined to the 

 spinous processes of the vertebrae, and 

 are formed from distinct centres of ossifi- 

 cation. These rays, as they are called, 

 are sometimes destined to grow to so 

 considerable a length, as to require being 

 subdivided into many pieces, in order to 

 lessen the danger of fracture, and also to 

 allow of a greater degree of flexibility. 

 These rays assume branched forms from 

 the farther subdivision of their parts. 

 Bridg. Treatise. 



RAY. In botany, the florets composing the 

 margin of a compound flower form the ray. 



REA'GENT. A term used in chemistry for 

 a certain body employed to ascertain the 

 component parts of other bodies, either 

 as regards the quantity or quality of such 

 component parts. 



RE'ALGAR. (realgar, Fr. arsenic rouge.) 

 The Hemiprismatischer Schwefel of Mohs ; 

 Rothes-rausch gelb of Werner ; Arsenic 

 sulfure rouge of Haiiy. Red sulphuret 

 of arsenic. Arsenic combined with sul- 

 phur forms realgar and orpiment, which 

 are found as natural ores ; the realgar is 

 of a beautiful and variable red. Realgar 

 is a bi- sulphuret of arsenic, consisting of 

 arsenic 69 '0, sulphur 31 "0. Specific 

 gravity 3'27. It occurs iji regular crys- 

 tals, in compact masses, in concretions, 

 or in crusts, which are sometimes earthy. 

 Before the blow-pipe it melts easily, 

 burns with a blue flame and garlic smell, 

 and soon evaporates. Nitric acid de- 

 prives it of its colour. It occurs in veins 

 in primary, transition, secondary, and 

 volcanic rocks ; in Sicily, Germany, Ame- 

 rica, and other parts. 



RE'CENT FORMA'TION. Any formation, 

 whether igneous or aqueous, which can 

 be proved to be of a date posterior to the 

 introduction of man is called recent. Re- 

 cent formations are marine, fresh-water, 

 and volcanic. Of recent marine formations, 

 we may instance the coral formations of the 

 Pacific ocean ; the deltas of the Ganges, 

 Po, &c. Of recent fresh-water forma- 

 tions, the deposits in many lakes ; Italian 

 travertin, &c. Of recent volcanic forma- 

 tions, the lavas of the different volcanoes, 

 which have been in action since man was 

 introduced. A fine specimen of recent 

 limestone from Gaudaloupe, containing a 

 fossil human skeleton, may be seen in the 

 British Museum. 



RE'CENT PE'RIOD. That period of time 

 commencing with the introduction of man 

 upon this earth. 



