CENTENARY 



CENTIPEDE 



63 



Centenary. rnn-iMin^ of a hundred ( Lat. 



cent inn i, a period of a hundred years, w now UHually 



cmplo\ ed to signify a commemoration of an event, 



birth (sometimes the death) of a great man. 



'I'll.' centenary of Burns 'H birth was celebrated in 



: the ftt-centenary of Pope in 1888 ; the ter- 



(eiitenaiv of Shakespeare in 1864. The centenary of 



Aiiieiii-.-iii Independence was celebrated by a Cen- 



tinninl Kxhibition in 1876; the ocJo-centenary of 



tin- Mologna I niversity in 1888. 



< Vnlrriim. the framework upon which an 

 iiivh in- vault of stone, brick, or iron is supported 

 during its construction. The simplest form of 

 centering is that used by masons and bricklayers 

 for the arches of common windows and doors. 

 This is merely a deal-lxmrd of the required shape, 

 ujion the curved edge of which the bricks or stones 

 of the arch are supported until they are keyed 

 in. In building bridges or other structures where 

 arches of great span are to be constructed, the 

 centering is usually made of framed timbers, or 

 timbers and iron combined. The arrangement of 

 tin- timbers should be such that the strain upon 

 each shall be mainly a thrust in the direction of its 

 length, for if the strain were transverse, a compara- 

 tively slight force would snap it, and if a longi- 

 tudinal pull, the whole structure would be no 

 stronger than the joints holding the pieces of 

 timber together. In arches of great span, a longi- 

 tudinal pulling strain is almost inevitable in some 

 parts, as a beam of great length would bend to 

 some extent under a thrusting strain. In such 

 cases great skill and care are demanded in the 

 designing and construction of the joints. As an 

 arch is built from the piers towards the keystone, 

 the weight upon the haunches during construction 

 tends to push the crown upwards, and therefore the 

 problem of designing a framed centering involves 

 the resistance of this tendency, as well as the sup- 

 porting of the weight of the materials. Occasion- 

 ally, when a very great span is required, and the 

 navigation will permit, piers are built on the bed 

 of the river, or piles are driven into it, to support 

 the centering directly, simplifying it, and at the 

 same time facilitating a more rigid disposition than 

 in centering supported only from the sides. See 

 article BRIDGE for descriptions and illustrations 

 of three types of centering : ( 1 ) that for the bridge 

 over the Dee at Chester, Vol. II., page 437, sup- 

 ported directly from the bed of the river ; also 

 the centering for the Ballochmvle Bridge; (2) 

 inclined struts in pairs supported from the sides, 

 as Rennie's centering for Waterloo Bridge, page 

 438; (3) trussed wooden girders supported from 

 the sides, as Rennie's centering for London Bridge, 

 page 438. 



Cupolas, like those of the Pantheon and St 

 Peter s at Rome, St Paul's in London, or the flat 

 domes of the Turkish mosques, require very effec- 

 tive centerings. 



Centigrade. See CELSIUS and THERMOMETER. 



Centipede, a general name for the members of 

 one of the orders of the class Myriopoda. Popu- 

 larly they are sometimes called Galley-worms, 

 technically Chiloooda. Like the Millipedes, which 

 form the most important neighbour order, the 

 Centipedes are segmented animals bearing jointed 

 appendages, having a well-defined head furnished 

 with feelers and jaws, and breathing by means of 

 air-tubes or tracheae. 



Structure. The Centipede is like a primitive 

 insect in its general structure. (a) Externals. 

 The body is divided into well-marked rings, but 

 the region behind the distinct head is practically 

 uniform, and not divisible into thorax and abdomen. 

 Just behind the head a few rings appear to be 

 fused. The number of rings varies from twelve 



to more than twelve times as manv. lo counting 

 the rings the ventral surface xhoufd }>e looked to, 

 for the dorsal shields often overlap. The rings are 

 flattened from above downward*, and each uean 

 a pair of appendages. Dorsally and ventrally the 

 skin is hard and liorny. Glands occur in various 

 positions. (6) Appendages. The head, which is 

 covered by a flat shield al>ove, bears ( 1 ) a pair of 

 antennae, usually of considerable length, and con- 

 sisting of from twelve to over one hundred joints ; 

 (2) a pair of small, strong, toothed, and bristly 

 mandibles; (3) a pair of under-jaws, usually with 

 palps. The next appendages are limb-like, and are 

 followed by a modified pair of legs, the basal pieces 

 of which generally meet in the middle line, while 

 the strong joints terminate in a sharp claw, at which 

 a poison-gland opens. These appendages are obvi- 

 ously of use for seizing and killing the prey. The 

 legs of the other segments are usually seven-jointed, 

 sometimes bear spurs and glands, and are generally 

 clawed. The last pair differ in size and form from 

 the rest, and are turned backwards. ( c ) Internal 

 Anatomy. The large brain is connected as usual 

 with a ventral chain of ganglia. Compound eyes 

 occur in one family, simple eyes in many, while 

 the feelers, certain bristles, and portions of the 

 skin are also sensory. In some cases there is a 

 special well-defined sense-organ of undecided func- 

 tion in front of the head, or on one of the jaws. 

 The alimentary canal is straight, and has asso- 

 ciated with it salivary and digestive glands, and 

 excretory (Malpighian) tubules. The heart is 

 represented by a chambered dorsal vessel. Tracheae 

 or air-tubes open on the sides of the body, some- 

 times on each ring, often on alternate segments, 

 ramify throughout the tissues, and are connected 

 together on each side by a longitudinal stem. 

 The reproductive organs are usually tubular, and 

 open on the last ring of the body. A distinct penis 

 is sometimes present. 



Life and Habit. Centipedes are darkness-loving 

 animals, nocturnal in their food-hunting, lurking 

 under stones or among rotten wood and the like 

 during the day. Their powers of vision are very 

 poorly developed, and most of the sensory work is 

 tactile. Only in one family ( Scutigeridae ) are there 

 compound eyes, in most forms only simple eyes, in 

 many none at all. The recent researches of Plateau 

 and others have shown that these creatures can 

 distinguish light from darkness, but do not need 

 eyes to do this ; species with eyes do not apparently 

 get on much better than those without them ; 

 those with eyes seem to perceive bright objects 

 reflecting much white light, and in some cases con- 

 spicuous movements, but probably in no case the 

 forms of objects. Moving actively about at nights, 

 feeling their way by means of their antennae, which 

 function as a blind man's staff, they light upon in- 

 sects, worms, and other small animals, which they 

 seize and kill with their poison-bearing appendages. 

 They are all voracious carnivorous forms, not 

 vegetarian like the Millipedes. Some forms can 

 run with some rapidity, and wriggle about in 

 curious serpent-like fashion. 



Development. In some cases the males are said 

 to deposit their reproductive elements in packets 

 ( spermatophores ) fixed by a web to the ground. 

 In most cases copulation probably occurs. Scolo- 

 pendra is viviparous, the others lay eggs. The 

 eggs develop into larva?, which are either minia- 

 ture adults ( Scolopendridse and Geophilidae), or 

 differ from the full-grown forms in having only 

 seven pairs of legs ( Scutigerida? and Lithobiida- ). 



Classification and Forms of Interest. The order 

 of Centipedes is one of the three or four divisions 

 of Myriopoda (q.v.), and, like the class, generally 

 represents a somewhat low grade of development 

 among animals breathing by air-tubes. The most 



