VERMES. 



tions and dilatations than any other part of the fyftem : 

 although their parietes are no thicker than thofe of the other 

 veflels, their enlargements may be called hearts ; but as they 

 are not found in all worms, it would be more exaft to fay 

 that the circulation is carried on in thefe animals by the 

 veflels only, without a heart. If, however, the exiftence of 

 a heart be admitted, at leaft in the lumbricus maiinus, it muft 

 be'confidered as double, and, like that of the two preceding 

 claffes, aortic. 



The aphrodite, amphinomia:, and nereids, differ from the 

 lumbricus marinus, only in having a greater number of pul- 

 monary velfels correfponding to the greater number of 

 brauchije. But in the fpecies which have their branchiae 

 on the neck, as the amphitrite, the pulmonary vefTels form 

 four trunks, two arterial and two venous, coming from the 

 trunks, which extend the whole length of the body, upon 

 the inteftine, and fimilar to thofe which have been de- 

 fcribed in the lumbricus marinus. 



The colour of the blood is more difficultly perceived in 

 the leech, becaufe it is paler and lefs contrafted with the 

 ground of the body ; yet the veflels may be eafily diftin- 

 guifhed, and injefted with mercury. There is a large longi- 

 tudinal veflel on each fide, communicating together, both 

 towards the belly and back, by tranfverfe branches, the 

 ramifications of which, dillributed in the Ikin, probably 

 ferve for refpiration, as no other organ can be found out. 

 Along the back we obferve a middle and flender veflel, not 

 fo immediately connefted to the two others, as they are to 

 each other, and producing branchiae on each fide. This 

 probably belongs to the arterial, and the two others to the 

 venous fyfl;em ; but their connexion has not been hitherto 

 difcovered. 



Longitudinal veflels, producing ramifications filled writh a 

 fine red blood, may be feen in the earth-worm. 



Movements of fyfl.ole and diaftole are very manifeft, and 

 quickly performed in all thefe red-blooded worms. 



Echlno-dermata I have not, fays Cuvier, been able hi- 

 therto to arrive at any clear notions concerning the arrange- 

 ment of the vafcular fyftem in this order ; but the following 

 is the refult of my refearches. 



The inteftinal canal of the holothuria tubulofa is twice 

 folded, and confequently forms three portions. The middle 

 of thefe has a veflel at its fide, diminifliing towards the two 

 ends. It receives numerous fliort veflels from another tube, 

 which will be defcribed laft ; and it produces from the oppo- 

 fite furface others, which are much fubdivided, and whofe 

 branches are at laft united into an equal number of fmall 

 veflels to end in a fecond trunk, which will be defcribed. 

 The net-work produced by this fubdivifion of the branches 

 of the fiift veflel, before they end in the fecond, is intimately 

 interwoven with the fmall branches of a hollow ramified 

 organ ending in the cloaca, and probably concerned in refpir- 

 ation. This organ can be diftended with water, or emptied 

 at the will of the animal, and thus probably admits of the 

 blood being afted on by the air. The firft; veffcl, then, 

 would be a pulmonary artery, and receive the blood from the 

 body to tranfmit it to the lung. We have feen the branches, 

 by which it receives blood from the inteftine ; that of the reft 

 of the body comes from a veflel, which will be defcribed 

 third in order, having been brought by veins which are per- 

 ceived over the whole mefentery. 



The fecond great trunk is divided into four great branches, 

 united by a tranfverfe one : two receive the blood from the 

 lung, and run parallel to the firft trunk, but at a diftance 

 fuited to the fubdivifions of branches which go from one to 

 the otlier. Thefe two branches are a kind of pulmonary 

 veins : they convey the blood, which has undergone the 



aftion of the lung, into the two other branches by the tranf- 

 verfe canal, and by their extremities ; for there is a vifible 

 communication between them. Thefe other branches, which 

 confequently perform the office of aorta, run along the firft^ 

 portion of inteftine, fending blood to it by an infinity of fmall, 

 but rather long arteries, which feem to terminate imme- 

 diately in the body of the inteftijie. The fuperior branch, 

 arriving at a certain height, is bifurcated, and its two rami- 

 fications are joined fo as to form a circle round the oefopha- 

 gus, from which five arteries go off to the mafs of the 

 mouth and the general covering of the body. The blood 

 returns from this covering by veins, which fill the mefenteries : 

 but there is alfo a general trunk, which feems to form a kind 

 of vena cava. It is made up of four principal branches, 

 united by a tranfverfe one. Two of thefe branches, which 

 run along the firft portion of inteftine, receive the blood 

 from it ; and the two others tranfmit it to the pulmonary 

 veflel by the fmall branches already mentioned at the begin- 

 ning of the defcription. 



According to this reprefentation, the arrangement would 

 very clofely refemble that of worms. 



In the afteria and echini the fame approximation is ob- 

 ferved between the vafcular and digeftive fyftems. The 

 principal vein and artery equally run along the inteftinal 

 canal in the latter ; and they are multiplied in the former to 

 follow the caeca. 



Nothing like blood-veflels can be feen in the medufse. 

 " The fubftance of thefe zoophytes," fays Peron, " prefents 

 at firft view the appearance of a kind of jelly, more or lefs 

 diaphanous, confiftent, and agreeably coloured according to 

 the fpecies. Excepting the fines, lamellae, and veflels of the 

 lower furface of the umbella, their fubftance appears homo- 

 geneous, even when examined with the moil powerful 

 magnifiers. However it may be torn or cut, the appearance is 

 the fame, and no trace of internal veflels can be difcovered. 

 Such indeed are the denfity and homogeneoufnefs of this 

 matter, that we can hardly conceive it to be penetrated and 

 nouriflied by veflels." Annales du Mufeum, t. xv. p. 42. 



Organs of Refpiration. — Cuvier obferves that thefe exhibit, 

 in invertebral animals, the fame relations to the organs of 

 motion, and particularly to the force which animates thofe 

 organs, as in the vertebral clafles, and thus confirm the 

 theory which afligns the degree of motive power as a mea- 

 fure of the quantity of refpiration. Thus, the only clafs in 

 this divifion of the animal kingdom, in which moft of the 

 individuals have the power of flying, is that in which re- 

 fpiration takes place at all points of the body, in which the 

 tracheae convey air to all parts ; in fhort, infefts. In fome 

 of thofe which have no wings, and therefore do not fly, the 

 power of the mufcles is evinced by the rapidity of their 

 other motions. Let any one obferve the centipede running, 

 or the flea jumping, and he will acknowledge that they 

 belong to a clafs poflefling great mufcular power, as he would 

 judge of the oftrich and caflbwary, although they are birds 

 without wings. 



The mollufca, fuperior to infefts in their circulating 

 organs, and particularly in the central parts of their nervous 

 fyftem, have a circumfcribed refpiration ; they breathe only 

 by the lungs, and no portion of air is admitted into the reft 

 of the body. It is therefore only neceflary to compare the 

 flownefs of their motions, with their rapidity in infefts, to 

 eftimate the effefts of thofe differences in organization. 



Invertebral animals poflefs either lungs more or lefs analo- 

 gous to thofe of reptiles ; branchiae, fometimes fimilar to 

 thofe of fifties, fometimes to thofe of tadpoles ; or laftly, 

 tracheae, a kind of organ not known in the vertebral divifion. 

 The latter is peculiar to infefts j the former to a fmall num. 



ber 



