VERMES. 



other inftances, the proper opening of the mouth is fur- 

 rounded by a circle of flefhy fimbriae, more or lefs divided, 

 as in the fpondylus. 



The naked acephala, as the biphori, thalias, afcidias, &c. 

 have neither folds nor fringes. The mouth of the biphorae 

 has merely a circular and flefhy edge. 



In the brachiopoda (terebratulse and lingulae) lips do not 

 exift ; but their place is advantagcoufly fupplied by two 

 long ciliated arms. 



2. Probofcis. Several naked moUufca, as the doris, and 

 probably moll of the tcftacea, as the buccinum, murex, 

 voluta, &c. have a flefhy cylindrical or conical probofcis, 

 which they employ for feizing their food at a diilance. 

 The motions of this inflrument are not confined to flexion 

 and a limited elongation, as in the trunk of tiie elephant ; 

 but it is capable of being withdrawn into the body 

 by folding inwards within itfelf, and of being extended 

 again, like the finger of a glove, the horns of a fnail, or 

 many other parts of nioUufca. 



It may be reprefented as a cylinder folded inwards within 

 itfelf, or as two cyhnders, of wrhich one includes the other, 

 and the two fuperior edges are continuous, fo that in draw- 

 ing outwards the inner cylinder, it is elongated at the 

 expence of the other, and in pufliing it back again it is 

 fhortened, while the exterior is elongated. The latter effedl 

 takes place at the Infide, becaufe this outer cyLnder has its 

 inferior edge fixed to the parictes of the head. 



Tliere are feveral longitudinal mufcles divided into many 

 fhreds at their two extremities. They are fixed on one fide 

 to the parietes of the body ; and on the other to the internal 

 parietes of the inner cylinder in its whole length, and to its 

 very end. It is obvious that they will have the efFeft of 

 drawing inwards this cylinder, and the whole probofcis. 

 When it is thus rctraftcd, a large part of the inner furface 

 of the internal cylinder comes to form part of the outer 

 furface of the external cylinder : and the contrary takes 

 place when the probofcis is elongated or extended. The 

 infertions of the mufcles undergo correfponding variations. 



The elongation of the internal cylinder, by the unfolding 

 of the external, is effcdtcd by the proper annular mufcles of 

 the probofcis. They furround its whole length ; and by 

 their fucceffive contraftions thrufi it outwards. There is 

 one ftronger than the others where the external cylinder is 

 attached to the parietes of the head. When the pro- 

 bofcis is elongated, its retraftor mufcles, by afting partially, 

 can bend it to one fide or the other ; and the various portions 

 in this way antagonife each other. 



This defcription may ferve alfo for the murex tritonis ; 

 but the probofcis is much fliorter lljan in the buccinum. 



In thofc moUufca which have a probofcis, the (ifophagus 

 is very long, and loohly folded, that it may follow all the 

 motions of that inflrument : it forms in a manner a third 

 cylinder concentric to the two others. 



None of the cephalopodoiis, pteropodous, or acephalous 

 claffes have a probofcis : the part which has been fo named 

 in the cirrhopoda (the anatifae and balani) is the redlum. 

 The fuppofed probofcis whicli fome authors fpeak of in 

 feveral bivalves, is the canal for the conveyance of water into 

 the fhell : it is placed oppofite to the true mouth, and is an 

 organ of refpiration, not of deglutition. 



The Tongue It is very fingular in the cephalopoda and 



gafteropoda ; and has nothing parallel in the animal kingdom. 

 It is a membrane covered with prominent fpines or ridges 

 dircfted backwards, and capable of excrcifiiig a kind of 

 periflaltic motion, in v/hich the fpines arc alternately raifcd 

 and deprefled, fo as gradnally to propel the alimentary fub- 

 llanccs into the cefophagu:.. 



The tongue of the cephalopoda is placed between the 

 two mandibles : it is behind the jaws in fucii gafteropoda 

 as have thofe organs. This is particularly obfervable in the 

 tritonia, when the tongue immediately receives whatever 

 pafTes the cutting edge of tlic jaws. Others have it near the 

 opening of the mouth ; and thofe which have a probofcis, 

 have their tongue at the anterior extremity of that organ. 

 In that cafe it ferves, in fome degree, as an organ of mafli- 

 cation ; as it can cut the food more or lefs by means of its 

 hooks. 



The tongue varies much in length ; and there arc fpecies 

 in which we are at a lofs to afhgn an explanation for its 

 confiderable extent. In the halyotis, for ex.imple, it is half 

 as long as the body ; in the patella and turbo pica it is 

 nearly quite as long, and folded Hke the intefl;ines ; and, 

 what is remarkable, thtfe genera have no probofcis. In 

 thofe which have one the tongue is fliort. The arrangement 

 of the organ makes it impofTible for the animal to employ 

 more than the anterior part : but probably it may refemble 

 fome kinds of teeth, the pofterior part coining forwards, 

 and fucceeding to the other in proportion as it is worn 

 away in front. This conjefture receives confirmation from 

 the foft and nearly gelatinous ft;ate of the pofl;erior part : 

 we may fuppofe that it becomes firm when it comes into 

 ufe, as the teeth of quadrupeds which are to fucceed. All 

 this pofterior part is rolled up longitudinally, hke a horn. 



In the cephalopoda the tongue is oblong, and prolonged 

 pofteriorly into a long horn. In the aplyfia it is very 

 broad, heart-fhaped, and placed on two rounded eminences 

 ieparated by a groove. In the bullosa it forms a fmall 

 tubercle at the bottom of the mouth. 



The hard covering of this tongue is difpofed in a regular 

 and conftant manner in eacli fpecies. It confifts, in the 

 cephalopoda, of hooked fpines of equal length, arranged in 

 two lateral rows, and of a middle feries of fcales with ivc 

 points. 



In the ofcabrio, there is on each fide a feries of hooked 

 fcales, with three points, and of long, fharp, and hooked, 

 but fimple fpines. In the middle there are fmall tubercles. 



The turbo pica has tranfverfe, cutting, and denticulated 

 laminae. 



The tongue of the aplyfia is covered all over with fmall 

 hooked fpines, difpofed in the quincunx order. In the 

 onchidium there are very fine tranfverfe grooves, thcmfclves 

 marked with ftill finer ftrias of an oppofite direftion. The 

 arrangement is nearly the fame in the doris. A fimilar 

 ftrufture occurs in the fnail and flug, but it is io minute 

 that a ftrong glafs is neceflary to perceive it. 



The acephala have no proper tongue ; but there is a cir- 

 cular valve at the entrance of their cefophagus, dirccled to- 

 wards the ftomach, and capable of contributing povverfidly 

 to deglutition. It is very plain in the oyfter. Generally 

 thefe are mere tranfverfe folds, which diredt the food by 

 their periftaltic motion. 



The ^tlimenlary Cavil and its Appendages. — The allnienlar^ 

 canal of invertebral animals is compofed of the fame effential 

 parts as in thofe which have vertebrae. There is an iniernal 

 mucous furface, which in fome inftances afl'umes a callous 

 nature, and fometimes becomes villous, or has a papillary 

 texture ; a cellular ftratum external to this, analogous to 

 what fome have called the nervous coat of the mammalia ; 

 and a mufcular covering of variable thicknefs. A leading 

 difference is, that often the ferous or mefenteric coat, and the 

 mefentery itfelf, are wanting. There feems to be none in 

 feveral moUufca, and in the clafs of infefts, and we only- 

 meet with it again in theechino-dermata. Another difference 

 is, tliat the cellular ftratum ir, not alway* vafcular : it in fo 

 E 2 only 



