SIPHON, or SYPHON (

See also:

• LAT

Lat. sipho; Gr. vi4xov, a

See also:

• TUBE (Lat. tuba)

tube)  , an instrument, usually in the form of a bent tube, for conveying liquid over the edge of a vessel and delivering it at a lower level . The 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 glass, indiarubber, copper or lead, according to the liquid which is to be transferred . The simple siphon is used by filling it with the liquid to be decanted, closing the longer limb with the finger and plunging the shorter into the liquid; and it must be filled for each time of using . 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 water of an aqueduct across a valley and following the contour of the sides are sometimes called siphons, though they do not depend on the principle of the above instrument . In the siphon the long, white alimentary canal, crowded with mud . The mouth is devoid of armature, and passes without break into the oesophagus; this is surrounded by the retractor muscles, which are inserted into the skin around the mouth, and have their origin in the body-wall, usually about one-third or one-half of the body-length from the anterior end (figs. t and 2) . Their function is to retract the introvert, which is protruded again by the contraction of the circular muscles of the skin; these, compressing the fluid of the body-cavity, force forward the anterior edge of the introvert . The number of muscles varies from one (Onchnesoma and Tylosoma) to four, the latter being very common . The alimentary canal is U-shaped, the dorsal limb of the U terminating in the anus, situated not very far from the level of the origin of the retractor muscles .

The limbs of the U are further

twisted together in a looser or tighter coil, the 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 size, opens into the rectum . As is so often the case with animals which eat mud and sand, and 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 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 respiratory—there are no special respiratory organs . A so-called heart lies on the dorsal 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 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 pro- longed into a large 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 round the body in the skin and break up into a very fine nerve plexus .

There are no distinct ganglia, but ganglion cells are uniformly distributed along the ventral side of the

cord . The whole is anteriorly somewhat loosely slung to the skin, so as to allow free play when the animal is extending or retracting its introvert . A pit or depression, known as " the cerebral organ,' opens into the 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 low ridge running along the line of origin of the retractor muscles . The ova and the mother-cells of the spermatozoa break off from this ridge, and increase in size considerably in the fluid of the body-cavity . Fertilization is 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 egg-shell . This little creature, which has many of the features of a Trochosphere larva, swims about at the surface of the sea for about a month and grows rapidly . At the end of this time it undergoes a rapid metamorphosis: a, Funnel-shaped grooved tentacular 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, cilia, takes in a quantity of water into its body-cavity, sinks to the bottom of the sea, and begins life in its final form . The following genera of Sipunculoids are recognized:—(i.) Sipunculus .

This, with Physcosoma, has its

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 species, and the genus contains some 16-17 species . (ii.) Physcosoma (fig . 3) has its body covered with papillae, and usually numerous rows of minute hooks encircling the introvert . It is the most numerous genus, and consists for the most part of shallow-water (less than 50 fathoms) tropical and subtropical forms . They of ten live in tubular burrowings in coral-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 house; only one 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 deposit and thickened shield at the posterior end and at the base of the introvert, which is eccentric . (vii.) Cloeosiphon has a calcareous ring, made up of lozenge-shaped plates, round the base of its centric introvert .

(viii.) Petalostoma, a C a, Mouth . b, Ventral nerve-cord . c, " Heart." d, Oesophagus . e,

Intestine . f, Position of anus . g, Tuft-like organs . h, Right nephridium. r, Retractor muscles. j, Diverticulum on rectum . The body, and they are some- spindle-muscle is seen overlying times spoken of as " brown the rectum. tubes." There is a well- developed brain dorsal to the mouth; this gives off a pair of oesophageal commissures, which surround the oesophagus and unite in a median ventral nerve-cord which runs between the longitudinal muscles to the posterior end of the body . From time to time it gives off c', " Heart." d, Brain . e, Ventral, and e, dorsal re-tractor muscles . f, Ventral nerve-cord . g, Vascular spaces in tentacular crown .

minute form with two

leaf-like tentacles, is found in the English SIR (Fr. sire, like sieur a variant of seigneur,1 from Lat. senior, Channel . (ix.) Onchnesoma, with 2 species, and (x.) Tylosoma, with comparative of senex, " old "), a title of honour . As a definite style it is now confined in the dominions of the British crown to baronets, knights of the various orders, and knights bachelor . It is never used with the surname only, being prefixed to the Christian name of the bearer; e.g . Sir William Jones . In formal written address, in the case of baronets the abbreviation Bart, Bart. or Bt (baronet) is added after the surname,2 in the case of knights of any of the orders the letters indicating his style (K.G., K.C.B., &c.) . In conversation a knight or baronet is addressed by the prefix and Christian name only (e.g . " Sir William ") . The prefix Sir, like the French sire, was originally applied loosely to any person of position as a mere honorific distinction (as the equivalent of dominus, lord), as it still is in polite address, but Selden (Titles of Honor, p . 643) points out that as a distinct title " pre- fixed to the Christian names in compellations and expressions of knights " its use " is very ancient," and that in the reign of Edward I. it was " so much taken to be parcel of their names " that the Jews in their documents merely transliterated it, instead of translating it by its Hebrew equivalent, as they would have done in the case of e.g. the Latin form dominus . How much earlier this custom originated it is difficult to say, owing to the ambiguity of extant documents, which are mainly in Latin . Much light is, however, thrown upon the matter by the Norman-French poem Guillaume le Mareschal,3 which was written early in the 13th century .

In this Sire is obviously used in the

general sense mentioned above, i.e. as a title of honour applicable tc all men of rank, whether royal princes or simple knights . The French king's son is " Sire Loeis " (1 . 17741), the English king's son is Sire Richard li filz le roi " (1 . 17376) ; the marshal himself is " Sire Johan li Mareschals " (17014) . We also find such notable names as " Sire Hubert de Burc " (ll . 17308, 17357) and " Sire Hue de Bigot " 1 species, have no tentacles, only one brown tube, and only one retractor muscle . Both genera are found off the Norwegian coast . The last named is said to have numerous papillae and no introvert . is "'st 1, Lophophore . 2, Pigmented pit leading to brain . 3, Section of dorsal portion of mesoblastic " skeleton." 4, Pit ending in eye . 5, The brain .

6,

Blood-sinus of dorsal side surrounding brain and giving off branches to the tentacles . 7, Collar . 8, Retractor muscle of head . 9, Hook . Io, Sense-organ . II, Nerve-ring . AurHoRIT1Es.—Selenka, " Die Sipunculiden," Semper's Reisen (1883), and Challenger Reports, xiii . (1885); Sluiter, Natuurk . Tijdschr . Nederl . Ind. xli. and following volumes; Andrews, Stud . Johns Hopkins Univ. iv .

(1887–1890) ;

Ward, Bull . Mus . Harvard, xxi . (1891); Hatschek, Arb . Inst . Wien, v . (1884) ; Shipley, Quart . J . Micr . Sci. xxxi . (189o), xxxii . (1891), and xxxiii .

(1892); P . Zool .

Soc . London (1898), and Willey's Zoological Results, pt . 2 (1899); Horst, Niederland . Arch . Zool., Supplementary, vol. i . (A . E .