VERMES. 



only in the mollufca, worms, and fome echino-dermata. 

 In no cafe have infefts any thing more than trachea rami- 

 fied in the parietes of their inteflines, and moil zoophvtes 

 have nothing at all. A third, but lefs general difference 

 is, that the memb^nes of the ftomach are often armed with 

 hard parts, either fimply in the form of plates, as in the 

 bullaea ; or of teeth, as in tlie cruftacea ; or of fcales, as in 

 the grylli ; or hooks, as in the aplyfia. This is a new 

 analogy between the inteilinal membranes and the Ikin ; for 

 we know, that in thefe animals, the (hells and fcales which 

 cover them, are often produced by the induration of their 

 rete mucofum. 



In its relative length, in the fize of its different parts, in 

 the number and form of its dilatations, and particularly of 

 the liomachs and csca, and in its internal folds, the ali- 

 mentary canal of invertebral animals exhibits varieties alto- 

 gether analogous to thofe obferved in the vertebral claffes. 

 Thus, for example, fuch as are carnivorous, have a fimple 

 and fliort canal, Sec. 



There is more variety in the pofition of the anus. The 

 zoophytes, fome echino-dermata excepted, have none at all, 

 but void their excrement by the mouth. Infefts, worms, 

 and cruftacea, always have an anus at the extremity of the 

 body oppofite to the mouth, and below. In the mollufca 

 its pofition feems fubjeft to no rule. In the doris we find 

 it backwards and upwards ; backwards and downwards in 

 the onchidium. It is on the right fide in the fliig, fnail, 

 aplyfia, and bullaea ; in the head, in the patella ; in front 

 of the neck, in the cuttle -fifh ; on the fide of the neck, in 

 the clio : in the acephala it is ufually found oppofite to the 

 mouth. 



Alimentary Canal of the Mollufca. — Locomotion is per- 

 formed in all the cephalopoda with the head downwards : as 

 the mouth is in the centre of the feet, the food muft 

 af«end into the abdomen : the redtum defcends and opens 

 into a cartilaginous cloaca, or funnel, placed in front of 

 the neck, and ferving as a common receptacle for the 

 femen, the eggs, and the inky fluid. The cefophagus 

 paffes behind the liver, or towards the back ; and the retlum 

 ia front, or towards the abdomen : the reft of the canal is in 

 the bottom of the fac or abdomen. In the middle of the 

 cefophagus of the fepia oftopus, there is a confiderable dila- 

 tation, of which the parietes, though thin, are manifeftly 

 glandular : this is a true crop, analogous to that of birds ; 

 but they have nothing fimilar to the bulbus glandulofus of 

 birds. The ftomach is a gizzard in its general arrangement : 

 the parietes are covered by two mufcles nearly as Itrong as 

 thofe of the gizzard of the gallinaceous birds : its internal 

 membrane is equally thick, cartilaginous, and eafily fepa- 

 rated. The pylorus is near the cardia, and leads into a 

 fpecies of caecum, or, if that name ftiould be preferred, a 

 third ftomach which is a little bent on itfelf in a fpiral form. 

 Here the hepatic canals terminate. The fecond, or true 

 pylorus, is near the other, and alfo near the cardia. A 

 fmooth canal lies along the concavity of the third ftomach : 

 the reft of its internal furface is plaited tranfverfely, and 

 exhibits the orifices of an infinite number of fmall mucous 

 follicles. The intcftine itfelf has thin fides : it is large, 

 and nearly of uniform diameter throughout. In the oc- 

 topus it makes two nearly tranfverfe convolutions, and a 

 large longitudinal turn before it proceeds ftraight to the 

 infundibulum. In the calmar it goes ftraight, without 

 any convolution. 



The alimentary canal prefents numerous varieties in the 

 gafiercpoda. It is moft fimple in the fnail and Aug. The 

 cefophagus, after being a little dilated to form a kind of 

 crop, ends at the ftomach, which is itfelf merely an oblong 



membranons bag, with a large hepatic canal opening in it; 

 The pylorus is near the fame part : the inteftine is cylin- 

 drical, and of uniform fize ; it makes two turns, and then 

 goes forwards and to the right, to open clofe to the orifice 

 of the lung, after having paffed along the parietes of that 

 cavity, and furnifhed numerous branches to the venous veffels 

 which are diftributed over thofe parietes. The fame relation 

 is obferved in the other gafteropoda between the inteftine and 

 the pulmonary organ : hence the anus is always near the 

 branchiae, when the latter are of limited extent. 



The parmacella differs only in having the anus, as well as 

 the pulmonary opening further back ; and the teftacella, in 

 having them quite at the pofterior extremity. 



There is a fimple membranous ftomach in the doris ; it is 

 an oval fac, into the bottom of which the bile is poured from 

 . numerous orifices. The pylorus is placed forwards, near 

 the cardia ; and the inteftinal canal, which is large and fliOrt, 

 goes directly backwards, almoft without any turn, to open 

 in the centre of the branchial circle, placed at the pofterior 

 part of the back. 



In the tritonia and phyllidia, the ftomach is as in the 

 doris ; but the inteftine goes forwards to the right, where 

 the anus ends under the edge of the cloak. The pylorus is 

 nearer to the cardia, and the anus more anterior, and nearer 

 to the generative orifice, in the phyllidia : it is feparate, and 

 placed further back, in the tritonia. 



The halyotis has merely a membranous fac at the back of 

 the bodv. The canal is uniform throughout, and runs twice 

 and a half the length of the body, nearly in three ftraight 

 hues. It opens by a flefhy tube in the cavity of the 

 branchiae, on the left of the body. 



In the buccinum the cefophagus is long and flender, has 

 a fmall lateral crop, and foon after ends in a rounded fto- 

 mach. The inteftine is very ftiort. When it has reached 

 the right fide of the branchial cavity, it is dilated into a 

 large tube with thick fides, of which the internal furface is 

 plaited longitudinally : it contrafts fuddenly before opening 

 at the anus. 



The ftomach of the murex is a flight membranous dilata- 

 tion. The reAum is not dilated, but fituated as in the buc- 

 cinum. The inteftine is ftiort. 



The ftomach of the patellae is a fcarcely fenfible dilatation ; 

 the bile enters by numerous pores. In the ofcabrio it is a 

 rounded fac. The inteftinal canal in both thefe genera is 

 flender and long ; and makes many convolutions. 



In the helix ftagnalis the ftomach begins to be more com- 

 plicated. It is funiiftied with two mufcles united by com- 

 mon tendons, and radiated exactly as in the gizzard of 

 birds. Immediately before entering it, the cefophagus is 

 dilated into a kind of crop. 



The onchidium alfo has a thick gizzai'd, preceded by 

 a crop. Two hepatic canals open into the latter, and 

 a third into the former. The gizzard is followed by two 

 membranous but thick ftomachs ; one is pyramidal, with the 

 broad part turned towards the gizzard, and parietes deeply 

 plaited into longitudinal ridges : the other is narrower, cy- 

 lindrical, and more dehcately plaited. 



There is fome analogy between the ftomach of the pleuro- 

 branchus and that of the onchidium ; but the organ -is 

 weaker in the former. There is at firft a membranous crop, 

 which is a mere dilatation of the cefophagus, receiving, 

 clofe to the opening of the fecond ftomach, the biliary fluid : 

 then comes a fmall gizzard, with mufcular but weak parietes : 

 this is followed bv a third ftomach, which refembles, by the 

 thin longitudinal lamina; of its inner furface, the third fto- 

 mach (nianyplus, feuillet, Fr. ) of the rurfiinantia. I^iftiy, 

 there is a fourth ftomach, fimply membranous like the firft, 



but 



