VERMES. 



and contraAion of the mufcular parietes of the bag : thus it 

 is renewed in the braachis. The latter are two large pyra- 

 mids, placed at the lide of the peritoneum, with their bafe 

 towards the bottom of the fac, and the apex towards the in- 

 fundibulum. Each is attached by a membranous ligament 

 to a mufcular column which adheres to the fac, and fends a 

 procefs to each of the plates of which the pyramid is com- 

 pofed- The pulmonary artery, arifing from the lateral 

 heart of its own fide, afcends along the external edge of the 

 branchia, giving two aiteries to each plate. The pulmonary 

 vein, which terminates in the intermediate heart, defcends 

 along the internal fide of the branchia, receiving two veins 

 from each plate. The plates themfelves are arranged one 

 over the other, parallel to the bafis of the pyramid : their 

 figure is triangular, and the two furfaces exhibit rows of 

 pencils, filaments, or minute ramifications, which are the 

 ultimate divifions of the pulmonary veflels. Each branchial 

 pyramid of the calmar has as many as fixty of thele plates, 

 while we find only nine in the oftopus ; but in the latter the 

 rows of filaments are more minutely ramified, and form much 

 thicker ftrata. 



Refpiration mud be effe&ed by the admiffion of water to 

 the branchia, and by its penetration among all the fine pro- 

 .cefles of their furfaces ; in the fame way, in fhort, as in 

 other inftances. 



Inftead of branchise, the brachiopoda have a circle of fmall 

 triangular plates attached to each lobe of the cloak. 



Among the pteropoda, the hyalaea has them concealed in 

 the two folds of the cloak ; they reprefent vafcular ramifi- 

 cations on the wings of the clio ; and in the pneumodermon 

 they are fmall plates, forming various hnes on the furface of 

 the abdomen. 



In the Angular animals called anatifje and balani, there 

 are found, on each fide, at the bafis of the arms or tentacula, 

 conical plates, equal in number to that of the arms, but 

 having a contrary direftion, namely, towards the back, and 

 lying againil the body under the cloak. Their relation to 

 the vafcular fyftem has n9t yet been determined. 



Thus we find, in all the moUufca, as complete an appa- 

 ratus for refpiration as for circulation. An extraordinary 

 additional or fecondary office of the branchije is that, which 

 they perform in fome acephala, of affording a receptacle, 

 for a certain time, for the ova, and even for the young when 

 hatched. 



Organs of Refpiration in IVorms Leeches and earth- 

 worms, as well as the thalaffema, have no other apparatus 

 for breathing but the fkin and its vafcular net-work : but in 

 other genera there are ridges or tufts, in which the veflels 

 are ramified. Thofe which fwim freely in the water have 

 the organs equally arranged on the two fides, along a more 

 or lefs confiderable portion of the back. Such as five in 

 tubes have them ufually placed on the head, that they may 

 be more eafily expofed to the water. 



In the aphrodite aculeata they are fmall iiefliy crifts, flightly 

 refembUng that of the cock, fituated above each of the tu- 

 bercles, wi'.ich fupport briilles. There ai'e forty pairs. 

 In the fcaly aphrodite they are fmall bundles of filaments. 



In the nereids there are fra,dl flefhy cones, amounting to 

 two or three on each fide of a ring : the blood-veffels are 

 ramified in them with wonderful delicacy. Sometimes, in- 

 flead of thefe fmall cones, there are true filaments grouped 

 into pencils, of three, or feven, or even in the form of 

 tufts. Sometimes there are fmall thin plates. 



In the terebella flava the branchiae reprofent bipinnated 

 leaves, and have a beautiful rofe -colour. There are thirty 

 pairs. In the tetraedra and carunculata there are merely 



large fafciculi of fil/ments. Their number in all thefe ge- 

 nera is the fame as that of the rings of the body. 



The arenicola (lumbricus marinus) has only fourteen pairs 

 occupying the middle of the back, and refembhng fmaU 

 clofe bufhes, of the fineft carmine when diftended with 

 blood, and becoming pale agam when empty. 



The terebella have branchis in the form of fmall clofe 

 trees ; there are only three pairs, fituated in the back, near 

 the head. 



In the amphitrite'there are two pairs in the fame fituation, 

 but (haped like feathers, very thick. 



They form, in the ferpulx, at the fides of the mouth, 

 two beautiful fan-like procefTes, with feathery branches, 

 having long ftems and fhort barbs, and exhibiting the fineft 

 colours. The number of feathery procefTes, as well as the 

 general curvature of the fan, varies according to the 

 ipecies. 



The fabellx (amphitrite ventilabrum, Linn., &c.) have 

 fan-like branchiae, as well as the ferpulae. Sometimes the 

 fan has a fpiral turn. 



In thefe animals each branchia has a vafcular, arterial and 

 venous fyftem, as in the higher clafTes. But we come to an 

 end here of refpiration by expanfion of the vafcular fyftem. 



Refpiration of the Echino-dermata. — Monro regarded the 

 feet, or thofe cyHndrical and extenfile tentacula, by means 

 of which the echini, afterix, and holothuriae walk, as organs 

 for abforption of the furrounding fluid, at leaft in the firft 

 of thefe genera. Cuvier affigns this funftion, in the two 

 firft named genera, to organs much fmaller and more nume- 

 rous, which may be feen in a living afterias obferved in 

 water. Befides the great tentacula of the lower furface, 

 the whole integument briftles with fmall flefhy tubes, which 

 are withdrawn into fmall openings as foon as the animal 

 is taken out of water. They form a beautiful fpeftacle 

 in the large fpecies, coming out at all points : the very 

 fpines produce them by fmall apertures along their ftems ; 

 and while the minute tubes are extended, they refemble fmall 

 leaves of trees connefted to their branches. There are fpe- 

 cies in which they form tufts, &c. round thefe fpines. Thofe 

 tubes which are fituated on the fides of the feet, are gene- 

 rally longer than the others. It can hardly be doubted, 

 that they have the office of conveying water into the interior 

 of the body. 



The holothurije, at leaft the tubulofa, have no tubes 

 projefting externally, but they have an internal organ, 

 which muft be fubfervient, according to all appearance, to 

 refpiration. It is one or more membranous and hollow trees, 

 of which the trunk opens into the fame receptacle (cloaca) 

 as the anus. It enters the body, dividing and fubdividing, 

 until it ends at laft in fmall conical produiStions. The 

 branches fwell at intervals into veficles, which are generally 

 found more or lefs diftended with water. 



The holothuria tubulofa has a fingle trunk, divided from 

 its origin into two principal branches, of which one pro- 

 ceeds along the general covering, adhering to it by a kind of 

 mefentery ; the other runs among the inteftines, interweav- 

 ing its branches with the veflels already noticed. This con- 

 neftion is fo intimate, that it cannot be detached without 

 laceration : probably there is a communication at this point 

 between the nutritive fluid and the furrounding element. 



The holothuria pentaAes has two diftinft trunks, deeply 

 diWded into large branches ; other fpecies have only one, 

 which is not divided. 



All animals fituated below thefe in the fcale, are deftitute 

 apparently of refpiratory apparatus. 



The genera medufa and rhizoltoma, whofe numerous vef. 

 fels are expanded in the tliin edge of their difk, may pro- 

 bably 



