VERMES. 



Me, reaching the heart direftly, and without any previous 

 diviiion. Their cardiac orifices are furnifhed with two 

 membranous reftangular valves, analogous to thofe of the 

 venae cavi in the pulmonary hearts. 



The aortic heart is white, and of a firmer tifTue than the 

 two pulmonary hearts. Its form is oval in the longitudinal 

 direftion in the calmar ; tranfverfely in the oftopus ; and 

 like the trefoil leaf in the officinalis. Its internal parietes 

 exhibit numerous mufcnlar columns, decufiating in all direc- 

 tions. In the oftopiis it produces two principal arteries 

 and fome fmaller ones, aU arifing immediately from the 

 cavity, and not from a common trunk. The fuperior 

 afccnds nearly parallel to tlic vena cava, giving branches to 

 it, as well as to the furrounding parts. The inferior is the 

 largeft artery, and indeed analogous to the aorta : having 

 given branches to the lower part of the fac, it turns up- 

 wards behind the vifcera to the head, and fends ramifications 

 to the inteftines, liver, oefophagus, then terminates, near the 

 fleftiy mafs of the mouth", by a circle which furrounds the 

 oefophagus, and fnpphes the crop, the fallvary glands, the 

 mouth and feet. 



Gajleropodous Mollufca. r-ln aU thefe, without exception, 

 the pulmonary fyllem is exaftly inverfe of that of filhes : 

 that is, the heart is compofed of an auricle and a ventricle, 

 and it receives the blood from the lung to diftribute it over 

 the body ; while the heart of fifhes fends the blood from the 

 body to the lung. In other words, the gafteropoda poflefs 

 always a fimple aortic heart. All the veins of the body end 

 in one or two vena cav:e, which, as foon as they reach the 

 refpiratory organ, are changed into pulmonary arteries, with- 

 out this change being marked by a ventricle, nor even by 

 valves. ' It is exadtly the fame as the change of the trunk 

 of the inteftinal veins into that of the vena portanim. The 

 pofition and direftion of thefe veins are determined by that 

 of the pulmonary organ, which latter is ufually found in the 

 neighbourhood of the reftum, that they may receive more 

 readily the veins of the inteftines, which probably bring 

 the chyle with them. Large trunks alfo come from the 

 liver. 



Thus, in the doris, where the branchia; form a circle 

 rotind the anus, the vena cava having collefted the blood 

 from the whole body, and traverfed the liver, arrives above 

 the reiElum, and divides into brandies, which feparate like 

 radii to enter the bafes of the branchial tufts. Thefe 

 branchicE return the blood, which has undergone their ac- 

 tion, by velTels correfponding to thofe which brought it. 

 The auricle, which is fliaped like a pyramid with a very 

 broad bafis, has this bafis difpofed in a circular manner, and 

 receives the blood from the pulmonary veins. It conveys 

 this blood immediately into the heart, which is round, flat, 

 and placed on the back of the liver. The heart has valves 

 at its entrance and exit : the latter is the origin of a large 

 artery divided immediately into four branches. One is 

 turned back, and foon loll in the liver ; two others alfo enter 

 this gland ; the fourth, which is the continuation of the 

 trunk, goes direftly forwards, giving branches to the intef- 

 tine, ftomach, fahvary glands, organs of generation and 

 mouth, and is loft ultimately in the flefhy mafs of the foot. 

 The tritoniae and phyUidia have the lungs at the two 

 fides of the body, and the heart confequently in the middle, 

 towards the back. The auricle, placed at the back of the 

 heart, extends tranfverfely from one lide to the other. It 

 receives the blood from two or rather four pulmonary veins, 

 which extend on the two fides of the body, from one end 

 to the other, in the fubftance of the flefhy covering, and 

 receive the blood from all the branchial tufts. The latter 

 had received it from two arteries reaching in the fame way 



along the fide of the body, and placed parallel to the vein?> 

 Thefe pulmonary arteries coUeft the blood from the body 

 by fix large veins, three on each fide, coming principally 

 from the liver and inteftines. The veins of the mufcular 

 covering end in thefe trunks without quitting its fubilance. 

 Having thus received from the lung the blood, which has 

 circulated through that organ, the heart diftributes it over 

 the body bv three large arteries, one of which goes back- 

 wards into the ovary, another downwards to the liver and 

 inteftines, and the third forwards to the male organs of gene- 

 ration, the mouth, and the flefliy mafs of the foot. 



The onchidium has fome refemblance to the tritonia. 

 Two veftels are formed in the fame manner in the flefhy co- 

 vering oil the two fides, and they convey the blood of the 

 body into the lung ; but by their extremity only, fince the 

 lung itfelf is excavated in the back of the body. Thefe 

 velTels receive the blood from the vifcera by many fmall 

 veins entering feparately, and that of the flefhy covering by 

 others excavated in its thickncfs. The heart is near the 

 lung behind on the right fide. Its auricle is very large, and 

 furniftied with flefhy columns. The heart produces one 

 great trunk, which firft gives a branch to the liver and 

 vifcera, then a long retrograde one to the reftum and organs 

 of generation, which are fituated behind and on the right. 

 It afterwards pafTes in the collar of the cefophagus, and 

 gives two large branches to the general covering. The 

 right fends an artery to the fahvary gland of its fide ; the 

 left does the fame, and moreover one to the male organ of 

 generation : the trunk is then loft in the mafs of the mouth. 



The aplvfia poflefTes one of the moft curious circulating 

 fyftems. There is excavated on each fide, in the flefhy 

 covering, a large vefTel furrounded by mufcular bands de- 

 cufTating in every direftion : thefe veftels receive the blood 

 by ordinary veins from certain parts. Two come from the 

 gland which furrounds the fhell, and produces the purple 

 liquor : but it is very clear that they communicate imme- 

 diately with the abdominal cavity by feveral large holes. 

 Are the latter fhut during life by mufcular contraAion, 

 or by any fine membrane ? We do not hitherto know. 

 However this may be, the two large veifels unite behind, 

 and thus produce a third, which is the pulmonary artery. 

 This is alfo very large, and runs forwards along one fide of 

 the membranous triang^le which fupports the branchiae on its 

 two furfaces. It diftributes the blood to all the branchial 

 plates by a correfponding number of branches : this blood 

 returns by correfponding vefTels into the pulmonary vein, 

 fituated alfo in the branchial triangle, and terminating in 

 the auricle. The heart is fituated croffwife, along the 

 middle of the body, a little towards the left, inclofed in a 

 pericardium. The auricle is large, thin, tranfparent, and 

 ilrengthened by mufcular fafciculi, which intercept lozenge- 

 fhaped fpaces. The ventricle is oval and thick, and has 

 ftrong mufcular columns : it has valves only at its entrance, 

 they are reftangular. The artery is divided at its exit into 

 three principal trunks. The firft goes to the left, for the 

 liver and inteftines ; the fecond forwards to the ftomach ; 

 the third and longeft remains longer in the pericardium, in- 

 chning towards the right. It pofTefTes in this fituation a 

 very extraordinary apparatus of unknown ufe ; namely,- a 

 double crifta filled internally with ramifications, arifing from 

 the artery itfelf, and filled by injefting the artery. They 

 appear to have blind terminations ; and the liquid they con- 

 tain appears to pafs back fimply into the vefTel, vv'ithout 

 entering any veins. After quitting the pericardium, this 

 artery gives a branch for the correfponding part of the muf- 

 cular covering, then goes direftly forwards under the oefo- 

 phagus. Arriving at the crop, it fends a retrograde branch 



to 



