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See also:SIPHON, or SYPHON (See also:Lat. sipho; Gr. vi4xov, a See also:tube)
, an See also:instrument, usually in the See also:form of a See also:bent See also:tube, for conveying liquid over the edge of a See also:vessel and delivering it at a See also:lower level
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The See also:action depends upon the difference of the pressure on the liquid at the extremities of the tube, the flow being towards the lower level and ceasing when the levelseoincide
.
The instrument affords a ready method of transferring liquids
.
The tube is made of See also:glass, indiarubber, See also:copper or See also:lead, according to the liquid which is to be transferred
.
The See also:simple See also:siphon is used by filling it with the liquid to be decanted, closing the longer See also:limb with the See also:finger and plunging the shorter into the liquid; and it must be filled for each See also:time of using
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Innumerable forms have been devised adapted for all purposes, and provided with arrangements for filling the tube, or for keeping it full and starting it into action automatically when required
.
Pipes conveying the See also:water of an See also:aqueduct across a valley and following the See also:contour of the sides are sometimes called siphons, though they do not depend on the principle of the above instrument
.
In the siphon
the See also:long, See also: The limbs of the U are further See also:twisted together in a looser or tighter coil, the See also:axis of which may be traversed by a " spindle muscle arising from the posterior end of the body . No glands open into the alimentary canal, but a diverticulum, which varies enormously in See also:size, opens into the rectum . As is so often the See also:case with animals which eat mud and See also:sand, and See also:extract what little nutriment is afforded by the organic debris therein, the walls of the alimentary canal are thin and apparently weak . All along one See also:side is a microscopic ciliated groove, into which the mud does not seem to enter, and along which a continuous stream of water may be kept up . Possibly this is See also:respiratory—there are no See also:special respiratory See also:organs . A so-called See also:heart lies on the dorsal See also:surface of the oesophagus; it is closed behind, but in front it opens into a circumoesophagealring, which gives off vessels into the lophophore and tentacles . The contraction of this heart, which is not rhythmic, brings about the expansion of the tentacles and lophophore . This See also:system is in no true sense a vascular system ; there are no capillaries, and the fluid it contains, which is corpusculated, can hardly have a respiratory or nutritive function . It is simply a hydrostatic mechanism for expanding the tentacles . The excretory organs are surface of the tube is See also:pro- longed into a large See also:sac lined with glandular excretory cells . The organs are typi- cally two, though one is often absent, e.g. in Phas- colion . They serve as channels by which the re-productive cells leave theminute circular nerves, which run See also:round the body in the skin and break up into a very See also:fine See also:nerve plexus . There are no distinct ganglia, but ganglion cells are uniformly distributed along the ventral side of the See also:cord . The whole is anteriorly somewhat loosely slung to the skin, so as to allow See also:free See also:play when the See also:animal is extending or retracting its introvert . A See also:pit or depression, known as " the cerebral See also:organ,' opens into the See also:brain just above the mouth; this usually divides into two limbs, which are deeply pigmented and have been called eyes . Sipunculoids are dioecious, and the ova and spermatozoa are formed from the modified cells lining the body-cavity, which are heaped up into a See also:low See also:ridge See also:running along the See also:line of origin of the retractor muscles . The ova and the See also:mother-cells of the spermatozoa break off from this ridge, and increase in size considerably in the fluid of the body-cavity . Fertilization is See also:external ; and in about three days a small ciliated larva, not unlike that of the Echiuroids, but with no trace of segmentation, emerges from the See also:egg-See also:shell . This little creature, which has many of the features of a Trochosphere larva, swims about at the surface of the See also:sea for about a See also:month and grows rapidly . At the end of this time it undergoes a rapid See also:metamorphosis: a, See also:Funnel-shaped grooved tentacular See also:crown leading to the mouth . b, Oesophagus . c, Strands breaking up the cavity of the tentacular crown into vascular spaces . it loses many of its larval organs, See also:cilia, takes in a quantity of water into its body-cavity, sinks to the bottom of the sea, and begins See also:life in its final form . The following genera of Sipunculoids are recognized:—(i.) Sipunculus . This, with Physcosoma, has its See also:longitudinal muscles divided up into some 17-41 bundles . It has no skin papillae . The members of this genus attain a larger size than any other See also:species, and the genus contains some 16-17 species . (ii.) Physcosoma (fig . 3) has its body covered with papillae, and usually numerous rows of See also:minute hooks encircling the introvert . It is the most numerous genus, and consists for the most See also:part of shallow-water (less than 50 fathoms) tropical and subtropical forms . They of ten live in tubular burrowings in See also:coral-See also:rock . The following three genera have their longitudinal muscles in a continuous sheath :—(iii.) Phascolosoma, with some 25 species, mostly small, with numerous tentacles . (iv.) Phascolion, 10 species, small, living in mollusc-shells and usually adopting the coiled shape of their See also:house; only one See also:kidney, the right, persists . (v.) Dendrostoma, with 4-6 tentacles, a small genus found in tropical shallow water . (vi.) Aspidosiphon, with 19 species, is easily distinguished by a calcareous See also:deposit and thickened See also:shield at the posterior end and at the See also:base of the introvert, which is See also:eccentric . (vii.) Cloeosiphon has a calcareous See also:ring, made up of See also:lozenge-shaped plates, round the base of its centric introvert .
(viii.) Petalostoma, a
C
a, Mouth
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b, Ventral nerve-cord
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c, " Heart."
d, Oesophagus
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e, See also:Intestine
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f, Position of anus
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g, Tuft-like organs
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h, Right nephridium. r, Retractor muscles. j, Diverticulum on rectum
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The body, and they are some-
spindle-muscle is seen overlying times spoken of as " See also:
minute form with two See also:leaf-like tentacles, is found in the See also:English See also:SIR (Fr. sire, like sieur a variant of seigneur,1 from See also:Lat. See also:senior,
Channel
.
(ix.) Onchnesoma, with 2 species, and (x.) Tylosoma, with See also:comparative of senex, " old "), a See also:title of See also:honour
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As a definite See also:style it is now confined in the dominions of the See also:British crown to baronets, knights of the various orders, and knights See also:bachelor
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It is never used with the surname only, being prefixed to the See also:Christian name of the See also:bearer; e.g
.
Sir See also:
In this Sire is obviously used in the See also:general sense mentioned above, i.e. as a title of honour applicable tc all men of See also:rank, whether royal princes or simple knights
.
The French See also: 6, See also:Blood-sinus of dorsal side surrounding brain and giving off branches to the tentacles . 7, See also:Collar . 8, Retractor muscle of See also:head . 9, See also:Hook . Io, Sense-organ . II, Nerve-ring . AurHoRIT1Es.—Selenka, " See also:Die Sipunculiden," See also:Semper's Reisen (1883), and Challenger Reports, xiii . (1885); Sluiter, Natuurk . Tijdschr . Nederl . Ind. xli. and following volumes; See also:Andrews, See also:Stud . Johns See also:Hopkins Univ. iv .
(1887–1890) ; See also: (1892); P . Zool . See also:Soc . See also:London (1898), and Willey's Zoological Results, pt . 2 (1899); See also:Horst, Niederland . See also:Arch . Zool., Supplementary, vol. i . (A . E . |
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