VERMES. 



ven' hard ; but it becomes gradually fofter behind, and 

 forms a long flexible tail. This foft part has a filky, or 

 even metallic luftre, and is torn by the flighteft effort. 



The form of teeth juft defcribed, is that which we find 

 in the echinus elculentus. In other fpecies, as the echinus 

 cidaris, inftead of being prifmatic, they are like half tubes, 

 and their extremity, which is worn away obliquely, forms 

 the bowl of the fpoon. 



All the echini, properly fo called, and apparently all the 

 fubgenera, which have the body fpherical and the mouth 

 central, have a mouth conftrufted in the manner jull de- 

 fcribed. Such as have the mouth central, and the body 

 flattened (clypeaiter, Lamarck ; echinus rofaceus), have an 

 oval mafs compofed of five offeous pieces, each fupporting 

 a tooth : but this mafs is quite flattened, like a circular 

 cake divided into five feftors. The faces, by which the fee- 

 tors touch each other, are not ilriated. Although there 

 are fibres to unite them, they are merely perforated by fine 

 and regular pores. The furface oppofite to the opening is 

 elevated at the fides into fine and prominent laminae ; the other 

 furface is fometimes like this. Their teeth do not Aide m 

 grooves, but are fixed, and have the (hape of a comprefTed 

 cylinder, worn obliquely at the end which is in action. 

 The oppofite end is foft, as in the preceding inftance, but 

 not prolonged into a flexible tail. The external mufclcs 

 which aft on this apparatus are very trifling. 



Such echini as have the mouth oblique, and furnifhed 

 virith a plate of the fliell advancing under it, as the fpstan- 

 guis and caffidula of Lamarck, have neither teeth nor offeous 

 mafs to fupport them. There is merely round the opening 

 of the mouth a ikin furnifhed with fmall fcaly pieces, firnilar 

 to thofe of the fliell, but not fo clofely fet as to render 

 this part inflexible j it can, on the contrary, be extended 

 and retrafted to a certain point, at the will of the animal, 

 like a probofcis. 



The afteris have no teeth : their mouth is a round mem- 

 branous aperture, leading to the ftomach by a very fliort 

 oefophagus, which is fometimes capable of being everted, 

 particularly when the animal is hungry. Thofe fpines of 

 the external furface, which are ncareft to the mouth, may 

 ferve, when inclined towards that opening, to retain the 

 prey : but they cannot be regarded as teeth in the proper 

 fenfe of the word. 



The opening of the mouth in the hblothuriae is furrounded 

 by a ring compofed of ten femi-offeous pieces ; but they 

 ferve merely as points of fupport for the longitudinal muf- 

 cles of the body and the tentacula. They are covered by 

 the internal integument of the mouth, fupport no teeth, and 

 are not concerned in the bufinefs of maftication. 



The fipunculi have no hard parts in the mouth, nor elfe- 

 where : neither have any of the zoophytes, which come next 

 in the fcale. 



Salivary Organs. 



In the Mollufca. — They are very large in the cephalo- 

 poda and gafl;eropoda ; more confiderable indeed than in 

 any other animals. In the former there are two pairs. 

 The firft and fmalleft is fituated on the flefliy mafs of the 

 mouth : each gland has a fliort excretory duft, penetra- 

 ting the mafs laterally, a httle in front of the origin of the 

 oefophagus. The other pair is much larger, fituated under 

 the neck, behind the liver, and oppofite the crofs. The 

 excretory dufts of the two glands unite into one tube, which 

 afcends beliind the oefophagus, and penetrates the mafs of 

 the mouth towards the pofterior point of the fmall cartilage, 

 which fupplies the place of a tongue. Thefe glands are 

 whitifti, flattened, and but little granulated. They are lo- 



bulated, and have an angular outline ; and they receive large 

 branches from the principal artery. 



In general, the gafteropoda have only a fingle pair of thefe 

 glands. In the common fnail (helix pomatia), they are ob- 

 long, placed clofe to tlie origin of the oefophagus, and pro- 

 duce two long canals, which increafe in fize as they are in- 

 ferted in the mafs of the mouth above. In the red Aug 

 they are lefs, and merely form a collar round the origin of 

 the ftomach. 



In the aplyfia, the falivary glands are two long, narrow, 

 ribbon-like bodies, floating at the fides of the oefophagus. 

 They are inferted in the mouth, near the origin of the fto- 

 mach, without having any part of their excretory duft un- 

 covered. Their pofterior extremity is fixed to the fecond 

 ftomach by means of branches received from the itomachic 

 artery. 



The doris has falivary glands fhaped like a long narrow 

 ribbon, attached behind to the ftomach. They are fo flen- 

 der in fome fpecies, that they might be taken for nerves, 

 when they have paffed through the nervous collar of the 

 brain. 



Anim.als of the genus bullsea, though very firnilar to the 

 aplyfias, have merely two fliort lender glands ; but in the 

 ciio borealis they are nearly the fame as in the aplyfia. 



In the pneumodermon they are elongated, and contrafted 

 where they pafs under the brain : for in all thefe animals, 

 without exception, eitlicr the gland, or at leaft its excretory 

 canal, paffes with the oefophagus through the cerebral ring. 



In the tiitonia they are very large and lobulated, fituated 

 at the fides of the oefophagus, and tolerably wide in their 

 middle. The ftrufture is firnilar in the onchidium. They 

 are generally confiderable in the aquatic univalves, as in 

 the genera bulimus, murex, and buccinum, which is remark- 

 able, inafm.uch as in aquatic vertebral animals they are either 

 fmall or entirely deficient. They are fmall in the halyotis. 



In the Echino-dermaia The holothurias have all round 



their mouth oblong Wind pouches, which terminate in that 

 cavity, and mufl; be fuppofed to pour into it fome liquor 

 analogous to faliva. There are twenty of different lengths 

 in the holothuria tremula. The pentaftes has only two, 

 much larger. Nothing of the kind has been difcovered in 

 the echini and afteriae. 



The medufae and other radiaria, and the zoophytes pro- 

 perly fo called, exhibit no falivary apparatus. 



Organs of Deglutition. 



In the Mollufca. — We muft diftinguiflj the external or- 

 gans or lips from the internal or tongue. The former are 

 again divided into two kinds ; viz. ftiort or proper lips, and 

 tubular lips elongated into a probofcis. 



I. Proper lips. In the cephalopoda, the opening of the 

 mouth is furrounded by a flefliy and denticulated circle, 

 Avhich covers and entirely conceals, when the animal choofes, 

 the two mandibles of the bill. 



In the gafteropoda, which have no probofcis, the mouth 

 is generally a longitudinal flit, whofe flefliy margins hold the 

 place of lips. Sometimes, as in the tritonia and onchidium, 

 thefe lips have the form of lliin plates, often divided into 

 flireds, as in the tritonia arborefcens ; the inferior tentacula 

 of the aplyfia may alfo be confidered as folds of its hps. 



All the common bivalves have round their mouth four 

 membranous folds, ufually triangular, and more or lefs elon- 

 gated, ferving apparently by their motion to convey the 

 food towards the mouth. One of their furfaces is, moreover, 

 fo vafcular, that it probably has fome conneftion with the 

 bufinefs of refpiration. Sometimes thefe folds are united, 

 two by two, in part of their length, as in the pinna. In 

 4 other 



