VERMES. 



ablenefs of the outer furfaces of teftaceous (hells during their 

 growth, and the continued renewal of their other furfaces 

 wliich admit of contaft with the living inhabitant ; next, 

 the ftains and coloured tranfudations which they often derive 

 from metallic falts, and other colouring materials placed in 

 their vicinity ; and laftly, that fuch occurrences do not 

 afFeft the living animal." See " Fafts and Obfervations re- 

 lative to the Conneftion between vafcularand extra-vafcular 

 Parts, in the Strufture of living organized Bodies." Lond. 

 Med. Repofitory for Auguft, 1814. 



It is ftated of fome teftaceous mollufca, that they quit 

 their (hell to form a new and larger one. Cuvier affcrts this 

 of the cyprasas, and it is alfo fuppofcd to be the cafe with 

 thebalani. (See Annalesdu Mufeum, t.i. p.470. ) Inthefe 

 inllances it is cleeu- that the furface of the body niuft form 

 the new {hell. 



The inhabitant of the paper nautilus (argonauta argo) 

 does not adhere to its fhell at any point ; the additions to 

 the (hell cannot therefore pofTibly be made by the way of 

 developement. It grows, in all probabihty, by a fccretion 

 formed by its two palmated arms. Nautili are met with 

 where extenfiTe fraftures have taken place, and have been 

 cop.folidated by depo(ition from within. Hift. des Mol- 

 lufqucs, par Denys Montfort, t. iii. p. 284. 



The animal comes out of its egg with the (hell ready 

 formed ; it pofTefles one turn, and fometimes rather more, 

 but is very thin. Leeuwenhoeck firft afcertained the (aft 

 refpedting oy iters. Lifter made the fame obfervation, and 

 extended it to other teilacea, both terreftrial and aquatic. 

 MarQgH, Rumphius, Swammerdam, Reaumur, and Adan- 

 (on, con(irmed the difcovery. The latter naturalift (hewed 

 that the viviparous teftacea agree with the oviparous, in 

 the circumftance of their young being covered by (hells at 

 the time of birth, and even before. Encycl. Method. 

 t. vi. p. 549. 



" As the animal grows afterbirth, its body advances con- 

 llantly towards the mouth of the (liell ; the pofterior end 

 quits the bottom of the (irft turn, to which it does not ad- 

 here, and when the fize of the (hell is complete, it occupies 

 a fituation very diftant from its original one. In fome 

 fpecies of an elongated figure, as the bulime confolide and 

 decolle, and feveral others, wliere the end of the fpire re- 

 mains very thin and unfupported, it is liable to break : the 

 animal flops the breach by a new calcareous exudation from 

 the pofterior end of its body. In other teftaceous mollufca 

 the end of the fpire becomes folid, and prefents a mafs of 

 laminated calcareous matter, fometimes as hard as marble. 

 The fucceifive layers are diftinftly viiible when a fcction is 

 made. I have now before me a fplendid fpecimen of the 

 trochus Niloticus, in which fix turns of the fpire are fohd, and 

 filled with a calcareous fubftance equal to the fineft Carrara 

 marble. I can demonftrate the fame h& in other ftiells. 



" In fome cafes diiferent phenomena are exhibited. The 

 murex tritonis not only has the apex of its long fpire con- 

 fohdated, but, as the animal grows older, and abandons more 

 rapidly the extremity of the fpire, infteaJ of filling up the 

 whole tube, it forms only thick fepta, which are conftrucled 

 fucceflively in the fituations where the animal's body refts 

 for a while." Hift. des MoUufques, par Denys Montfort, 

 t. iii. p. 246, et feq. 



Some white-blooded animals have hard parts internally ; 

 but they are not articulated fo as to form the bafes of 

 moveable members, and their texture differs confiderably 

 from that of ordinary bones. The common cuttle-fi(h 

 ( fepia officinalis ) contains in the fle(h of the back an oval 

 fubftance, convex before and behind, white, folid, friable, 

 and of a calcareous nature. This fubftance is not attached 



to the fle(h, but has the appearance of a foreign body intro- 

 duced into it. There is no indication of any. veflfel or nerve 

 entering it ; nor is any tendon affixed to it. It is compofed 

 of thin parallel lamellse, which are not in immediate contaft 

 with each other. The intervals are occupied by an infinite 

 number of fmatl hollow columns, ftanding perpendicularly 

 between one lamella and another, and arranged in very 

 regular quincunces. As the fuperficies of the lamellse are 

 plane, and thofe of the bone itfelf convex, they neceffarily 

 interfefl each other : the points of interfeftion are marked 

 on the furfaces of the bone by regular curvilinear ftrix. 

 Thefe bones have a kind of wings, which are of a lefs 

 opaque nature, lefs brittle, and have a greater refemblance 

 to thin elaftic horn, than the body of the bone. 



To this laft fubftance the part called the fword of the 

 calmar (fcpia loligo) bears an analogy. It is tranfparent, 

 elaftic, and very brittle ; its (hape is fometimes that of a 

 leaf, fometimes of a fword-blade. It bears the fame rela- 

 tion to the foft parts, and occupies the fame fituation as the 

 bone of the cuttle-fifh. 



There is a gradation in ftruftnre from this fword of the 

 calmar and bone of the cuttle-fifh, which are completely 

 internal, to the external (hells of the teftacea. The bulla 

 aperta (Linn.), bullxa (Lamarck), has a (hell contained 

 in its cloak or outer integument, and not vifible on the ex- 

 terior of the body. It is extremely thin, and almoft tranf- 

 parent ; not attached to the body by any mufcle, for it is 

 fo weak that the (lighteft mufcular force would break it. It 

 is ftriated, fo as to indicate fucceifive dcpofitions ; and fo 

 placed in the body as to cover the principal vifcera. (Cuvier, 

 Annalcs du Mufeum, t.i. p. 159. pi. 12.) The dolabella, 

 teftacella, and parmacella, have analogous (hells, called by 

 Cuvier coquillescachees. (Ibid. t. v.) There is a thin (hell 

 contained in the cloak of the pleuro-branchus. ( Ibid. t. v. 

 p. 270 ; pi. 18. B. fig. 3.) There is a fmall and thin cal- 

 careous plate in the back of the (lug, analogous to the com- 

 mon (hells. The fle(hy covering of the branchiee has a 

 larger but thin, horny, tranfparent and flexible plate in the 

 aplyfia. Ibid. t. ii. p. 297. 



The infulated bony or horny pieces juft enumerated, par- 

 ticularly that of the cuttle-fi(h, ftrongly confirm the repre- 

 fentation which has been already given refpefting the growth 

 of (hells. They muft increafe by ilrata fuccefQvely depo- 

 lited ; and they may thus be called internal (hells. 



The afterias and echinus have a kind of fl<eleton, the 

 nature of which very much refembles that of the mollufca. 

 In the echinus it is a fohd calcareous envelope, frequently 

 very hard. It has a number of Uttle holes, through which 

 pafs membranous feet, furnifhed with tubercles and points 

 analogous to the fubftance of the (hell, which play freely on 

 thefe tubercles. 



In the ftar-fi(h, the calcareous part forms a ftalk, com- 

 pofed of a number of fmall articulated vertebrse, which 

 extend under the middle of each of the branches of the 

 body, and te which is attached a kind of offeous grating, 

 which fupports the remainder of the envelope of the branch 

 to which it belongs, and which is rendered remarkable, even 

 externally, by its projeftion, and by the tubercles of dif- 

 ferent forms that cover the whole of its furface. 



Their offeous ftalk cannot be regarded as completely ex- 

 ternal, fince it is covered outwardly by an epidermis and 

 other foft parts. This is, perhaps, the moft ftriking excep- 

 tion to the general rule that white-blooded animals have no 

 internal articulated (Iceleton. The mode of growth of the 

 (Iveleton of the ftar-fi(h has not yet been iufficiently in- 

 veftigated : the (lieletou of fome holothurias is exaftly 

 fimilar. 



Corals, 



