VERMES. 



its liver divided into three diftin£l mafTee, of which the ex- 

 cretory dutts are not even united. The two firll terminate 

 in the firll ftomach by diftinft orifices ; the third opens into 

 the bottom of the gizzard or fecond ftomach. 



In the teftacella the liver is divided into two independent 

 maffes : their dudls are inferted oppofite each other, in the 

 beginning of the inteftine, not in the ilomach. 



The doris and phyllidia, which have a fimple membranous 

 ftomach, receive the bile in it by feveral openings. The 

 liver of the former is remarkable, inafmuch as it gives rife 

 to a fecond excretory vefTel, terminating on the outfide of 

 the body, near the anus. The objeil of this llructure is 

 not known. ' 



The fnail and iiug have enormous livers, divided into 

 many lobes and lobules, all which pour their liquor by a 

 common caaal into the bottom of the cul-de-fac formed by 

 the Ilomach behind the pylorus. The appearance of the 

 liver is remarkable, particularly in the (lug, from the con- 

 trail of its black furface with the fine opaque white of the 

 blood-veflels. The teftaceous gafteropoda have an equally 

 voluminous liver, filling, together with the generative or- 

 gans, the greateft part of the convolutions of the (hell. 



The liver of the acephala generally envelopes the ftomach, 

 like an incruftation on its furface : it pours the bile into 

 that cavity by numerous orifices. The patella among the 

 gafteropoda, and the clio and pneumodermon among the 

 pteropoda, have the fame ftrufture ; but the hyala, which 

 belongs alfo to the latter order, has its liver placed as in the 

 common gafteropoda, t,hat is, interwoven with the inteftine. 



Even in the acephala, the inteftine, after leaving the 

 ftomach, often returns to penetrate again the fubftance of 

 the liver. 



This form and difpofition of the liver are fotmd in the 

 naked acephala (afcidije and biphori;, as well as in the 

 others. In the brachiopoda (lingulas and terebratulx), the 

 hver is diftindl, connefted with the convolutions of the in- 

 teftine, and even with the mufcles. 



In all the moUufca, as in the red-blooded animals, the 

 bile is of a greeni(h-yellow, more or lefs ftrongly marked. 



Nothing analogous to a liver is found in the worms, unlefs 

 we confider the yellow fubftance in the parietcs of the 

 ilomach of the arenicola as fuch. The echino-dermata and 

 zoophytes have nothing which can be compared to this 

 gland. The liver then (cems to end with the moUufca, and 

 iome cruftacea : infects have a knid of fubllilute for it, and 

 zoophytes have nothing like it. In proportion as the 

 fundlion of refpiration is lefs confined, and extends to more 

 parts in the body, the liver ceafes more completely. 



Coverings and Supports of the intejlinal Canal. 



In the MoUufca. — We may aftert in general, that the 

 alimentary canal of the mollufca is not enveloped nor fup- 

 ported by a mefentery. The different convolutions are joined 

 together, and to the lobes of the liver, by cellular tiffue, blood- 

 veffels, and nerves, but not fixed to a membrane. Yet all the 

 vifcera are contained in a true peritoneum, which even forms 

 a diilinCl cavity for the heart, and alfo envelopes the lung, 

 when the latter is not entirely exterior ; but this peritoneum 

 is not folded inwards to cover the inteftine. 



The peritoneum of the gafteropoda nearly lines the whole 

 external ijit'^gument of the body : the latter is thick and 

 mufcular, and, tlierefore, protefls it elfeclually. In thofe 

 which have a (hell, the part of the body conilantly covered 

 by it is not furrounded by mufcles ; it is covered only by 

 peritoneum and a thin layer of flcin, and might almoil be 

 regarded as a natural hernia, formed by parts wliich have 

 protruded from the mufcular portion of the aniioal. 



In the cephalopoda the peritoneum is a bag contained in 

 another bag, namely, that which properly conftitutes the 

 body. But the latter does not entirely inclofe the former ; 

 its opening leaves the peritoneum uncovered in front, where 

 it is protected only by a thin continuation ol the (l<in. The 

 peritoneum of the cephalopoda is further remarkable from 

 the circumftance of its being perforated by two openings, 

 which communicate externally. There is no other example 

 of fuch a ftrudilure, except in the rays. As the cephalo- 

 poda have a head, feparated from the body by a neck, and 

 a true cartilaginous cranium, their peritoneum, \vhich docs 

 not reach beyond the neck, does not cover the brain, nor 

 the mafs of the mouth, as in the other mollufca. 



In confequence of the form of the body, the peritoneum 

 of the acephala occupies a fmaller fpace than that of the 

 other mollufca. It is furrounded by the mufcles, which rriy 

 to the foot ; and when there is no foot, it is fimply covered 

 by the (liin. Nothing like an omentum has been feen in any 

 animal of this clafs. 



Some worms, as the arenicola, have their alimentary 

 canal fupported merely by blood-veffels ; others, as the 

 earth-worm, have fmall tranfverie membranes connecting 

 the canal to the exterior covering of the body ; but a me- 

 fentery, properly fo called, exifts in none. A thin mem- 

 brane, forming an internal hning to the exterior integuments, 

 may be regai-ded as a peritoneum. 



In the echino-dermata we again meet with a perfeft me- 

 fentery, and even fometimes with a kind of omentum. The 

 mefentery of the echini is fixed to the (liell, and makes turns 

 exadllycorref ponding to thole of the inteftine, which it covers. 

 In the ftar-fi(h there are as many mefenteries as ramified 

 creca in the branches of the body. They adhere alfo to the 

 internal furface of the general covering, parallel to the axis 

 of the branch. In the holothuria tremula, the mefentery it 

 attached to the inteftine from the mouth ; it accompanies 

 the tube to the other extremity of the body, following one 

 of the longitudinal mufcles ; it then croffes, and returns to 

 the mouth, following a fecond ; croffes again, and re- 

 defcends to the anus along a third. Let it, liowever, be 

 remarked, that the numerous veffels of this animal are not 

 found in the mefentery, but on the oppofite furface of the 

 canal. The interweaving of thefe veffels with each other, 

 and with the refpiratory organs, forms a fingular fpecies of 

 omentum, concerned in the bufinefs of refpiration. 



The alimentary fac of the aftinis is fupported by feveral 

 vertical membranes, which furround it like radii, and are 

 fixed on the oppofite fide to the covering of the body. 



The medufx have no occafion for mefentery, tiieir ali- 

 mentary cavity being merely excavated in the gelatinous 

 mafs of their body : the frelh-water and other polypes ilill 

 lefs fo, inafmuch as their inteftine and body are one and the 

 fame thing, that is, fimply a bag formed of a gelatinous 

 membrane. 



Organs of Abforpt'wn. — No abforbing veffels can be dif- 

 covered in the lower claffes of animals now under our con- 

 fideration. Cuvier thinks that the yeins abforb in them ; 

 and he fupports his fentiments by the following ftate- 

 ment. 



We are firft, fays he, led to this notion by obferving 

 that the blood of thefe animals does not differ from wliat is 

 called lymph in the red-blooded claffes : and alfo by the 

 faft, that no anatomical method has hitherto enabled us to 

 demonftrate the exiftence in thefe animals of any but blood- 

 veffels. We have already obfervcd that the parts, called by 

 Poh lymphatic veffels, belong to the nervous • fyftem. 

 There are, befides, fome pofitive reafons ; of which the- 

 principal is the natural communications of the great cavities 



of 



