VERMES. 



two thin nmfcles are fltuated, one btlow the other, the 

 fibres of which are tranfverfe. One arifes in the middle 

 longitudinal line of the foot, on the fide oppofitc to the 

 fuckers, and proceeds direftly to its infertion in the fame 

 line of the adjacent foot on either fide. The other arifes 

 below the fuckers themfelves, goes over the lateral parts of 

 the foot, and at laft forms a mufcular membrane with 

 tranfverfe fibres, which pafFes under the preceding mufcle, 

 and proceeds to its infertion in the other foot, exaftly 

 in the fame manner as it took its origin. This double 

 mufcular membrane bears fome analogy to that which unites 

 the toes of web-footed birds, Inch as ducks, geefe, &c. It 

 produces a circular plate, which occupies the intervals be- 

 tween each bale of the feet. Thefe two mufcks probably 

 ferve to bring the feet nearer to each other ; the fecond 

 may befides feparate the two rows of fuckers. It reaches 

 the whole length of the foot, but becomes thinner towards 

 the extremity. 



Below thefe three layers of mufcles (the two tranfverfe 

 and the cutaneous), we find another pretty large one, the 

 conical figure of which determines the fhape of the foot. 

 At the furface it feems entirely formed of tranfverfe fibres ; 

 but on cutting it in different directions we find that it has 

 longitudinal fibres. Tliele fibres are interwoven like thofe 

 of the human lingual mufcle towards its centre. In the 

 centre of thi^ mufi.Ie there is a vacant fpace, in which we 

 find very large vefltls and nerves. The fuckers are fattened 

 to the inferior furface of this mufcle, and to a layer of fibres 

 llill more evidently longitudinal, by little flL-fliy bands, dif- 

 fering in direftion according to the fpecies. 



The fuckers are formed by a mufcular cup of radiated 

 fibres, which, by their contradlion, diminifh its capacity. 

 But at its edge, and clofe to the plate under the cylindrical 

 mufcle, tiierc is another layer of circular fibres, hke a 

 fphinfter, which renders the cup more convex. Finally, 

 each fucker is retained and moved upon the foot by little 

 mufcular fafciculi interlaced together, and uniting at laft in 

 the inferior tranfverfe mufcle of the foot. At leaft, this is 

 the cafe in the fepia odlopus. 



In the calmar (fepia loligo), and the cuttle-fifh (fepia 

 officinalis), the fuckers arc attaclied by very fmall mufcular 

 peduncles. 



When an animal of this kind approaches any body with 

 its fuckers, in order to apply them more intimately, it pre- 

 fcnts them in a flat or plane ftate ; and when the fuckers are 

 thus fixed, by the adaptation of furfaces, the animal con- 

 traiSs the fphinftcr, and forms a cavity in the centre, which 

 becomes a vacuum. By this contrivance, the fucker ad- 

 heres to the furface with a force proportioned to its area, 

 and the 'weight of the column of air and water of which it 

 forms the bafc. This force, multiplied by the number of 

 fuckers, gives that by which all or a part of the feet adhere 

 to any body. The power of adhcfion is fuch, that it is 

 eafier to tear off the feet than to feparate them from the 

 fubllance to wliich the animal choofes to attacli itlelf. 



In the cuttle-fifh and the calmar, the mouth of the fucker 

 is fnrrounded by a cartilaginous indented zone ; in the 

 oftopus it is only a fltfliy diflc, fiat, ar.d perforated in the 

 middle. 



Befides the eight feet juft defcribed, which are all that 

 are poffefTed by the odlopus, the cuttle-fifli and calmar have 

 two others much longer and fmaller, and without fuckers, 

 except at the extremity, which is enlarged. Their ftrutlure 

 is in other refpects the fame as that of the other feet. 



The organs of locomotion in the gaftcropodous moUufca, 

 rcfide principally in that inferior part of the body on which 



they drag themfelves forwards, and which is called their 

 foot. It is a flclhy mafs, formed of fibres which crofs each 

 other in fevcral din dtions, and are capable cf giving it every 

 pofTible (hape. Mod commonly it has that of an oval, 

 pointed behind ; but, bv the various contr^ftions of which 

 thffe fibres r.re fiilciptible, they cxtLiid or contraft it in 

 the whole or in part, lo as to produce that (lew progreffive 

 motion, which every body has remarked in the common 

 fnail or Aug. The tranfverfe fibres are rafily fetn in the 

 foot of the fiug, if it be opened by the hack. They pro- 

 ceed from the edges of the foot to two longitudinal middle 

 tendinous lines. Below thefe we meet with others in a con- 

 trary direftion ; but fo interwoven, that it is difficult to 

 trace the layers. 



In the fcyllafa the foot is only a longitudinal furrow, im- 

 prefTed in the whole length of the belly of the animal. By 

 the help of this furrow it embraces the flalks of fucus, upon 

 which It crawls. In other refpefts, the organizatioH of its 

 foot is nearly the fame as that of the fiug. 



In the limpet (patella), the inferior layer is compofed of 

 tranfverfe fibres, which are interlaced at the edge with 

 numerous circular ones. The fuperior layer confifis of two 

 rows of fibres, meeting at an acute angle on a middle line, 

 which correfponds to the long diameter of the foot. There 

 are alfo foire circular fibres at its edge. The inferior layer, 

 by its contraftions, lengthens the ellipfis of the foot, while 

 it leffens the breadth ; and the inferior diminifiies the length, 

 but increafes the breadth. This is the mechanifm which 

 produces the progreflion of thefe animals. Laftly, the cir- 

 cular fibres diminifii the furface on all fides, and render it 

 convex above, thereby producing a vacuum, which makes 

 the animal adhere firmly to the furface that fupports it. So 

 powerful is this adhefion, that we cannot feparate a limpet 

 from the rock by means of the fingers. 



Reaumur tied a ftring round the limpet, called by the 

 French osil du bouc (patella Grseca), and fufpended a 

 weight from it perpendiculai-ly. Thirty pounds w^ere nc- 

 ceffary to feparate the fhell ; and this weight was fupported 

 by the animal for a ftiort time. Reaumur conceives that 

 the adhcfion is not produced on the principle of forming a 

 vacuum, but by a vifcous fluid ; and ftates, that when the 

 (hell and animal were fplit vertically, the divided portions 

 ftill adliered. (Mein. de I'Acad. des Sciences de Paris, 

 171 1, p. 109, et fcq.) In this reprefentation we are fa- 

 tisfied that this able obfervt^r was mirtaken. 



The gafteropodous mollufca, which arc furnifhed with 

 (hells, poflefs, befides the mufcles juft defcribed, others 

 that enable them to retreat into the (liell, and protrude 

 their body from it again. Thefe (hells, or moveable habi- 

 tations, vary much in their form. They are generally 

 made of one piece, of difFeront fliapes, fimple, without 

 twifting, in the limpet ; in a flattened fpire, as in the 

 planorbis ; in a globular and pyramidal fpire, as in the 

 (hell of the fnail, bulimus, dipper-fnail, &c. T!ie chiton 

 is the only genus of gafteropoda which has a (hell formed of 

 fevcral pieces. 



In the limpet the foot is faftcned to the circumference of 

 the (hell by a ring of fibres attached all round the (hell, and 

 wiiich, after piercing the outward covering or cloak, .ire 

 inferted in the edges of the foot, and interlaced witli its 

 circular fibres. They leave a fpace in front, for the pafTage 

 of the head.' This mufcle, by its contrat^iona, brings the 

 foot and the fliell clofcr together, and compreffe! the body ; 

 on relaxing, it allows the (hell to be raifitl up by the elaf- 

 ticity of the body. 



In the garden-fnail there are two Hfong mufcles, which 



draw 



