VERMES. 



quillee des Animaux tant ten-eftres qu'aquatiques, foit de 

 Mer, foit de Terre." He followed up the fubjetl, in anfwer 

 to fome objections, in the Memoirs for 17 16, p. 303 : under 

 the title " Eclairciflemens de quelques Difficultcs fur la 

 Formation et I'Accroiffementdes Coquilles." 



" When (fays the author) the aninrial, which filled its rticll 

 exatlly, increafes ia i'lze, and the fhell is confequently in- 

 fufficient to cover it entirely, a part of the furface muil be 

 expofed. This is the part neareft to the opening, for the 

 animal's body can be augmented only in that direftion. The 

 inhabitants of a ipiral (hell, as fnails, grow only in the di- 

 reftion of the head, or towards the opening of the (hell ; 

 while thofe which occupy bivalve (hells, as mufcles, can in- 

 creafe in their whole circumference. In both cafes it is the 

 uncovered portion of the body that produces the fiiell." 

 Mem. de 1709, p. 367. 



" That the animal really grows before its (hell, in the 

 way juft pointed out, may be eafily feen in the garden- 

 fnails at their feafon of increafe. We obferve that the (hell is 

 too fmall. The animal fixes itfelf againft a wall, or remains 

 at reft, and « part of its body manifettly extends beyond 

 the (hell all round." Ibid. p. 370. 



He illuftrates the natural growth by the procefs employed 

 for repairing injuries. " After breaking away a portion of 

 the (hell, which can be eafily done without injuring the 

 animal, as it adheres only at one point, we obferve the 

 creature foon attach itfelf to ■ the fides of the vedel in 

 which it is placed. A fine pellicle, which may be com- 

 pared to the web made by the houfe fpider in the angles of 

 walls, covers the body in twenty -four hour.s, and forms the 

 firll flratum of the new (hell. In a few days this is 

 thickened by feveral ftrata produced under it ; and, at the 

 end of about ten or twelve days, the new portion of (hell 

 has nearly the thicknefs of the original part." P. 371. 



" If," he obferves, " the injury were repaired by means of 

 materials furnifhed by the broken edge, as in the cafe of a 

 fraftured bone, we (hould obferve a callus produced from 

 that margin, and extending gradually into the centre of the 

 aperture. But the edge, in faft, remains unaltered, and the 

 matter dcpofiled is on the furface of the body." P. 373. 



That the body of the animal affords the materials by 

 which the Ihell is formed, is rendered more evident by the 

 following experiments. " I broke away a portion of the 

 fhell, and placed in the opening, between the animal's body 

 and the Ihell, a portion of !amb-(lcin leather, fuch as is ufed 

 to make what are called chicken gloves. I fattened this to 

 the internal furface of the (hell, fo that it completely (hut 

 up the opening intervening between the (hell and the ani- 

 mal's body. It is evident, that if the (hell itfelf produced 

 the materials of reftoration, the new fubftance ought to be 

 formed, in fuch circumftanccs, on the exterior furface of the 

 leather. On tiie contrary, however, that fide which was 

 towards the animal's body became lined with (hell, and none 

 was depofited on the exterior furface. 



" Again, I broke away a part of the (hell at its opening, 

 introduced a portion of the leather, and fallcned it to the 

 inner furface ; then turned it down, and faftcnod ic alfo to 

 the outer furface, fo that the circumference of the opening, 

 with its broken edge, was completely covered. Now, if the 

 fhell fp-ows by a principle of vegetation, either this covering 

 (hould have prevented tlie growth, or the elongation of the 

 (hell (liould have puOicd the leather forwards. On the con- 

 trary, the (hell grew, and the leather remained where it was 

 placed, being interpofed between the old (hell and the new 

 piece, to the formation of which the former confequently 

 could not have contributed." P. 374. 



" It is a necefTary confcquence of the preceding {i&.3, that 

 Vol. XXXVII. 



the (helli of fnails increafe in fixe, only by an addition to 

 the number of their fpiral turns, and that tlf length of a 

 turn, when once formed, continues always the fame. The 

 truth of this ftatement is eafily (hewn. If the (liell of a 

 full-grown fnail be reduced to the fame number of turns as 

 that of a young one of the fame fpecies, the two (hells arc 

 then of the fame fize. This holds true, even with refpeft 

 to the (hells of fnails juft produced. A turn more or lefs 

 makes a great difference in the fize of the (hell ; for the dia- 

 meter of each is nearly double that of the preceding, and 

 about one-half of the following ; hence half, or even a 

 fourth of a turn more increafes confiderably the fize of the 

 (hell." P. 378. 



The fame point has been attentively examined by Mr. 

 Carlifle, whofe conclufions confirm in all refpecls ihofe of 

 Reaumur. 



" The moft appofite illuftrations, and the moft pofitive 

 inftances of union between vital and extra-vital parts, are to 

 be found in the tellaceous tribe of animals. After a long- 

 continued and careful inveftigation, I am fully convinced, 

 that the (hells of all the vermes of Linnasus are extra-vaf- 

 cular from their commencement, and remain fo during the 

 whole of their connexion with the living creature. Tiie rirft 

 produ&ion and the growth of thofc (licUs always depend 

 upon a depofit of material thrown out from the iurtace of 

 the body of the living animal. The figure and colours of 

 the feveral parts of thofe fiiells, in every fpecies, depend 

 upon the fhape and the colouring glands of the modelling 

 organs. Fraftures are repaired by fpreading a crullaccous 

 fluid over the inner edges, and never by any exudation from 

 the fraftured parts, fince they retain always the fquared 

 broken furfaces after fuch repairs. Extraneous bodies are 

 equally covered with Ihell, whether they are in contaft with 

 the parent fhell or not. The firft may be feen in the fre- 

 quent envelopement of nereifes in the common oyfter ; the 

 latter has been often afcertained by the experiments made 

 for the purpofe of creating artificial pearls, and which 

 might, if fkilfuUy praftifed, yet prove very fucccfsful. 

 The borings of parafitical vermes into fhells are never filled 

 up, or the bored furface altered, unlefs fuch borings pene- 

 trate into the cavity where the living animal dwells, and 

 then the apertures are invariably plugged up or fmeared over 

 with pearly matter. The water-worn external furfaces of 

 old fhells, and other external abrafions, are never repaired, 

 which is to be feen in old Lving oyfters expofed to the 

 moving friftion of currents or ftrong tides, in the worn-oif 

 fpines of the pholas daftylus, and in the convex points of the 

 two valves of old mytili, efpecially the mytilus anatinus. 

 I have fought in the moft extenfive colleClions of the metro- 

 polis for examples of fradures and other injuries which have 

 occurred to the fliells of living vermes, and I have collefted 

 many remarkable fpccimcns. They all demonftrate the 

 fame refults without any exception. I have made numerous 

 experiments upon tlie garden-fnail, (helix nemoralis,) by 

 frafturing and breaking away the fliell in various parts, and 

 have always found the repairs to be effefted from within by 

 firft fmcaring over an epidermoid varnifh, and then by 

 plaiftcring the inner furface of that film with fuccefTive cal- 

 careous lamina:. I have in vain attempted to injcft the flicUs 

 of recent vermes from the vafcular parts of their bodies ; 

 and am fully fatisfied, that none of their albuminous or gela- 

 tinous tellaceous membranes were ever at any time tra- 

 verfed by vefTels ; indeed, they do not polfefs any of the 

 reticular texture or arborefcent pores which itfc common to 

 all vafcular parts ; but, microfcopically examined, they 

 rcfcmblc the cxuviol or epidermoid membranes. To thefe 

 may be added the notorious circumftance of the unchangc- 



C ablcncfs 



