SPI 



SPO 



a red colour, used as a precious stone. 

 "When it weighs four carats (about 16 

 grains), it is considered of equal 

 value with a diamond of half the 

 weight. 



SPINELLANE. A silicate of alu- 

 mina, said to be a variety of Haiiyne, 

 found on the shores of the lake of Laach, 

 in a rock composed of glassy felspar, 

 quartz, hornblende, &c. 



SPINI-CEREBRA'TA. The name 

 given by Dr. Grant to those \ertebrated 

 animals, of which the central parts are 

 in the form of a lengthened dorsal 

 nervous cord, developed anteriorly into 

 a brain, and protected by a vertebral 

 column and cranium. These are the 

 myelencephala of Owen. 



SPl'NNARETS. The articulated tubes 

 with which spiders construct their webs. 



SPINTHERE. A substance supposed 

 to be a variety of sphene. It occurs in 

 the department of I sere in France, in- 

 crusting calcareous spar crystals. 



SPIRACLES {spiraculum, a breathing 

 hole). The breathing pores in insects. 



SPIRAL (ffTreipa, any thing rolled 

 round on another thing). A curve which 

 turns round like a circle, but, instead of 

 ending where it began, it continues to 

 revolve, receding further and further 

 from the centre, like the spring which 

 moves the wheels of a watch. It may be 

 briefly described as a curve which winds 

 round a point in successive convolu- 

 tions. 



SPIRAL VESSELS. Trachenchyma. 

 Long cylindrical tubes, constituting the 

 vascular tissue of plants. Each tube 

 tapers to each end, and has an elastic 

 spiral fibre generated within it. 



SPIRE (o-Trelpa, a coil or spiral line). 

 A term applied, collectively, to the con- 

 volutions of a spiral shell which are 

 placed above the lowest or body-whorl, 

 whatever shape it may assume. In pla- 

 norbis the spire is sunk ; in cyprcca it is 

 so small as to be seen only when the 

 shell is young, after which period it is 

 covered by the enlargement of the body- 

 whorl. 



SPIRIT. A general term for all in- 

 flammable liquors obtained by distilla- 

 tion, now almost exclusively applied to 

 spirit of wine or alcohol. Ordinary spirits 

 contain from 50 to 52 per cent, of alcohol ; 

 spirits of wine, from 62 to 67 per cent. ; 

 rectified spirits, from 82 to 85 per cent. 



Spirit, proof. By the expression that 

 a spirit is any number, say ten, over 

 proof, is meant that 100 gallons of the 

 312 



spirit would bear the addition of ten 

 gallons of water to reduce it to proof 

 strength, or it would form 110 gallons of 

 proof spirit, t. e spirit of density 0-918633. 

 The term ten, under proof, means that 

 ten gallons of water must be taken from 

 100 gallons of the spirit to raise it to 

 proof, or that 100 gallons of it contain 

 only 90 gallons of proof spirit. 



SPIRIT-LEVEL. A glass tube nearly 

 filled with spirit of wine, and hermeti- 

 cally sealed at both ends. The exact 

 horizontal position ofits axis is ascer- 

 tained by the extremil;ies"bf the air- 

 bubble being at equal distances from the 

 middle point in the length of the tube. 

 The level is used for determining the 

 relative heights of ground at two or 

 more stations. 



SPIRU'LIDiE. A family of poly- 

 thalamous, decapodous, dibranchiate ce- 

 phalopods, consisting of the single genus 

 spirula, and named by Professor Owen. 



SPODIUM (o-TTodo?, a cinder). A 

 name sometimes given to the oxide of 

 zinc, which sublimes during calcination. 



SPO'DUMENE. Triphane. Prismatic 

 triphane spar; a silicate of lithia and 

 alumina, found in embedded crystalline 

 masses. 



SPONDY'LIDiE. A natural family of 

 marine conchifers, named from the genus 

 spondylus, which appears to be co-exten- 

 sive with the family itself. The fossils 

 of this family are very numerous, and a 

 somewhat wide geological distribution. 

 The genus plicatula is with diflJiculty 

 distinguished from spondylus. 



SPONGE [spongia). A porous sub- 

 stance, generally referred to the class of 

 poriferous animals. The sponge of com- 

 merce is the dry skeleton of the animal, 

 from which the gelatinous flesh has been 

 removed. 



SPO'NGIOLE or SPONGELET {spon- 

 giola, a little sponge). The absorbing 

 extremity of the fibril of a root, consist- 

 ing of extremely lax cellular tissue and 

 mucus. It is not a special organ, but 

 merely the newly formed and forming 

 tender tissue. The term spongiole is 

 also applied to the warty excrescence 

 often found near the hilum of seeds, and 

 is then nearly synonymous with stro- 

 phiola. 



SPORANGI'UM (o-Tropa, a spore, ay- 

 7etov, a vessel). The theca, or case, 

 which contains the spores of cryptogamic 

 plants : some writers consider this organ 

 to be formed by the adhesion of an ex- 

 ternal and internal series of organs, the 



