VERMES. 



of the cloak, behind one of the mufcles which clofe the 

 Ihella. Such is the cafe in the lolen, pholas, &c. 



The naked acephala have a fimple ftomach and (hort in- 

 teftine. In the afcidia, the latter makes only two convolu- 

 tions; in the biphori (falpa), it turas twice round the liver, 

 near which the anus is found. There is only one fpecies 

 (thalia) in which the canal is prolonged further, even to 

 the oppofite extremity of the body. The heart in this 

 family is never traverfed by the reftum. 



The brachiopoda ( terebratulae and lingulz) have a fimple 

 uniform canal. In the lingula it comes from the mouth, 

 which is between the two arms, and makes two turns before 

 reaching the anus, which is at the fide. It is nearly twice 

 as long as the body. 



Alimentary Canal of IVorms. — It is in general ftraight, 

 without any confiderable fnequalities, extending from one 

 end of the body to the other, and occupying nearly its 

 whole capacity. 



In the common fea-moufe (aphrodite aculeata), there is a 

 flefhy part in front, holding the place of a probofcis, and 

 capable of being extended out of the body : a miftake has 

 been committed in confidering this as a ftomach. A cy- 

 lindrical inteftine follows, of fmall diameter, but giving 

 origin on each fide to twenty long blind proceffes, be- 

 coming larger towards their blind end, which Is attached 

 between the mufcles of the feet and the lateral veflek. 

 This organization is the more remarkable, as nothing hke it 

 is met with in the neighbouring genera. 



The amphinomia capillata and tetraedra (terebella flava 

 and roftrata ) have firft a flefhy mafs of the mouth or a pro- 

 bofcis, rounder and ihorter than that of the aphrodite, then 

 a fmall oefophagus, and an enormoufly dilated ilomach, with 

 cellular panetes, like thofe of a colon, the folds of which are 

 fixed by a tendinous line placed on the ventral fide. It oc- 

 cupies two-thirds of the length of the body, and ends in a 

 large fhort inteftine. 



The arenicola, or worm ufed as a bait by fiftiermen 

 (lumbricus marinus, Linn.) has no fleftiy probofcis; the 

 oefophagus occupies one-eighth of its length ; the ftomach, 

 which is more dilated, occupies a third. It is of a fine yel- 

 low, with the furface divided into lozcnge-fliaped facculi, 

 the feparations of which are marked by veflels of a beautiful 

 red. The reft of the canal is fmall, fmooth, and ftraight. 



In the leech of frefti water (hirudo fanguifuga), an oefo- 

 phagus equal to one-eighth of the animal is followed by a 

 ftomach occupying one-half of its length : this organ is ca- 

 pacious, with thin fides, and divided by numerous mem- 

 branous diaphragms, which contrail it confiderably, leaving 

 only an opening in the middle. The inteftine is narrower, 

 and its internal membrane, which is opaque, exhibits an in- 

 finite number of fmall plaits ; it enlarges towards the anus, 

 which is very fmall, fo that its exiftence has been er- 

 roneoufly denied by fome anatomills. Two csca arife from 

 the pylorus, proceed parallel to the principal canal, and are 

 nearly as long. In tiie fea-leech (hirudo tuberculata), the 

 alimentary canal may be faid to enlarge from the mouth to 

 the oppofite end ; the exiftence of a ftomach is marked 

 merely by its fepta, which are wanting in the inteftine. 



The common earth-worm has only a long canal, divided 

 by numerous tranfveife fepta, which are even ftrcngthened 

 by membranes attaching them to the exterior covering of 

 the body. Some dilatations in front may reprefent a kind 

 of ftomach. 



The canal of the nereis is equally fimple, ftraight, and 

 conftriftcd at intervals : nothing more can be obierved in 

 the amphitrite, terebella:, and ferpulx. The tail which 



terminates the body of the genus amphitrite, contains the 

 reftum. Cuvier has, however, obferved in one fpecies of 

 amphitrite, which lives commonly on the oyfters, a very 

 thick and hard globular gizzard. 



In the lumbricus, thalaflema, and echinus, the canal is 

 five or fix times longer than the body, of equal diameter 

 throughout, with thin and corrugated fides. The pofterior 

 part IS filled with excrement, moulded into fmall ftiort 

 cylinders. 



Among the inteftinal worms, the afcaris has a very fimple 

 canal with thin fides, of nearly uniform diameter, and 

 fcarcely longer than the body. 



Alimentary Canal and Sac of Zoophytes. — In this clafs we 

 meet with alimentary canals pofiefiing both mouth and anus, 

 and others like a fimple fac, more or lefs complicated. The 

 firft arc even fupported by a true mefentery, which is not 

 found in infefts, mollufca, or worms. Such a ftrufture is 

 feen in the echinus and holotliuria. 



The canal of the holothuria tubulofa is four times the 

 length of the body, in which it makes a double convolution, 

 refembling the figure 8. It commences at the mouth by a 

 flight contraftion, then retains nearly the fame diameter 

 throughout. Its parietes are flender ; the anus opens into 

 the great cloaca fituated at the back of the body, and fepa- 

 rated from the cavity of the abdomen only by a valve : this 

 circumftance will be further confidered in fpeaking of the 

 refpiratory organs. A membranous mefentery attaches this 

 whole canal to the external coverings of the body. A fimi- 

 lar arrangement is obferved in the holothuria pentaftes. 



The fipunculus has a fmall uniform canal, going firft 

 ftraight from one extremity of the body to the other ; then 

 returning in a fpiral manner round this ftraight part, to ter- 

 minate at a lateral anus very near the mouth. It is fix or 

 eight times as long as the body. 



An alimentary cavity, conftituting a complicated bag, is 

 obferved in the afterias. It is a membranous fac, much 

 folded when empty, placed in the common centre of the 

 rays, and having no other opening but the mouth, lo 

 that the excrement is rejefted by the paftage which admits 

 the food. This bag has ten blind appendices or inteftincs, 

 minutely fubdivided into branches and ramifications, which 

 form a very beautiful objeft. Thefe are lodged in the rays 

 or branches of the body, two in each : when there are more 

 than five branches, there are alio more than ten of the rami- 

 fied c<Eca. Theie trees, or kind of bunches of grapes, are 

 fixed rays in their place by membranous mefenteries. 



The ailerix, whofe rays have no feet, but refemble 

 the tails of ferpents f ophiuri, Lamarck ), have no fuch caeca. 

 Their ftomach is a fimple bag, occupying merely the central 

 diflc of the animal : its membrane, however, exhibits in all 

 parts an infinite number of fmall facculi. Probably the 

 fame ftrucfure exifts in the kind called caput medufas. 



The ahmentary canal of the medufs is as complicated as 

 that of the afteriae ; but, iiiftead of being fufpended in the 

 great cavity of the body, it feems to be excavated in its fub- 

 ftance. The ftomach, which is very large, fills the bafis of 

 what is called the pedicle or diflc of the animal : tubes 

 proceed from it in a radiated manner towards the edges of 

 the luperior broad part of the body, which has the fhape of 

 a fegment of a fphere. Theie veffels communicate together 

 by lateral branches, and both furnifh an infinite number of 

 fmall ramifications, which form a very complicated net-work 

 over the whole body, conveying the nutritive fluid to all 

 parts, as blood-veffels do in other animals. This plexus is 

 particularly difcernible towards the edge of the umbella, 

 where it refembles a fpecies of lace. 



The 



