Ifi 



CONCHOLOGY. 



According to tliis opinion of Knorr, the (liell increafes 

 by addition oi- aggregation ; but it is more conlonant to 

 the finiple operations of nature to fuppol'e, that it is by 

 ejttenlion that the Ihell tal<es the fize adapted to the fpe- 

 cies, as well as to the growth of the animal. There is 

 certainly a fyllem of aiterics, as in all folid parts and 

 bonfs of animals, conjoined in the ihell, by_ which the 

 nouriOiing moiHure palTes to or from the inhabitant ; and, 

 according to this generital formation, every lyfteni of ar- 

 teries, with its particular organs, conforms to the llruc- 

 ture and wants of the included animal. 



As to the beautiful defigns and colours of fnells, Knorr 

 proceeds to explain them on the principles of animal 

 fluids. He fays that a matter flows from the animal into 

 the fliell, of a confillency like foam i different, at times, 

 in tlie fame aniinal, according to the difference of the 

 particular humours, and organical refervoirs ; jull as in 

 other creatures, where the blood is red, the liile green, 

 the urine yellow, the chyle white, Sec. Now, iftheoi- 

 ganiciil refervoirs, and the fmall veins, which ramify 

 thence near to the furface of the fliell, are difpofcd in cir- 

 cles, lines, or figures, the moifture being of another co- 

 Jotii-, cannot piefent itfelf on the furface but in the fame 

 colour. This moillure being Jiardened and .^ugmented 

 by continual addition through the fpaces of the fliell, 

 and thus more ditiolved, and as it were brought to per- 

 feflion, it muft be that the fl;etch or outline of the fliell 

 will (hew the true difpofition of the fibres, veins. Sec. 

 though only of a hair's breadth, and alfo the pores. It 

 cannot appear improbable that this fliould be the true 

 conftruttion of thefe creatures, becaufe we fee different: 

 ftriated and fpecklcd fnails, with and without fliells ; and 

 alfo fimilar lines and decorations in a great many Ipecies 

 of caterpillars. Hence, as the colours fpring from the 

 refleftion of the rays of light, perpetually made on the 

 plates of the furface, and which arife from the different 

 diffolutlons of the fmaUeft particles, this author does not 

 hefitate to attribute the colours of (hells to the llrufture 

 of their organical fecretories. And as every animal is , 

 fubjcfl' to certain difeafes, which can change and alter 

 the colour of their humours, and alfo by the funffions of 

 tiigeflion, dilTolution, fecretion, &c. io without doubt 

 fea animals are fubjeft to the fame mutabilities of nature, 

 ivhich thus become the caufes of their great variety of 

 colours. Thofe who, in order to explain the formation 

 and growth of fliell-tifli, fuppofe a fyliera of arteries, (ay 

 that the liquors which flow from the animal into the fliell, 

 although of one and the fame colour, can, by the petri- 

 fication that takes pl.ice fucceluvely in the extremities 

 of the fmalleft veins towards the exterior furface, take 

 different colours ; jutt as the fame nourifliing juices of the 

 human body can be differently coloured by the mixture? 

 and fecretions. The above reafoning is no lefs applica- 

 ble to figures and paintings, or to fmall variations of 

 ffru(5lure; (or the body or fibres of an animal may be 

 badly formed; it may have the pores Ifraight and large, 

 fo that it cannot ("ail to produce a dift'erence in the exter- 

 nal appearance of the fliell, which mull not on that ac- 

 count be taken for a different or (ubordinate fpecies. 

 This remark I'eems the more necefl'ary, in order that fuch 

 tilings might not contribute to increafe the genera and 

 fpecies of (hells unncccffarily, in a (yftematlcal divifion. 

 From a bare calculation made by Knorr, the data of 

 which he formed from the diverfnies of the colours of 

 ttioli fliells he had only in his own polTeffion, he makes it 

 yppear that there would be two thouland different fliells, 

 without counting the (pecies which muft be buried in the 

 bottom ot the lea, and which we know nothing of but 

 by tlic petrifications, which prove to us their exiltence. ~ 



JVI. de Reaumur appears to have given a fatisfaftory 

 account of the formation of the fliell of the garden fnaif, 

 founded oti a courii; of very ingenious experiments, re- 

 lated in the Pans Memoirs. He there fupports the theory 

 «f Knorr, by endeavouring to fliow, that this fubllance 

 is produced merely by the perfpirable matter of the ani- 



mal condenfitig and afterwards liardening on Its frnfict;. 

 and accordmgiy taking the figure of its body, which his- 

 performed the office of a mould to it; in (hort, that the 

 (hell of a fnail, and, as he (uppofes, of all other animals 

 pofl'cfTed of (hells, was only the product of a vifcous tr.iuf- 

 mlation from the body of the animal, containing earthy 

 particles united by mere juxtapufition. 



But it was M. Heiiflimt, in the M-moirsoS the Academy 

 of Sciences for 17166, who firfl difcovered the fliructure of 

 fliells to be organical. In the numerous experiments that he 

 made on an immenfe number, and a very great variety, of 

 animal (hells, he coiillantly found that they were conipoled 

 of two difliniSf (ubitances j one of which is a cretaceous 

 or earthy matter, and the other appeared,- from many ex- 

 periments made upon it by burning, diftillation, or other- 

 wife, to be evidently of an aniinal nature. Thefe two 

 (ubitances he dexteroufly feparated from each other by .^ 

 very eafy chemical analyfis ; by the gentle operation of. 

 which they were exhibited diftincSly to view, without any 

 material alteration from the aftion of the folvent, or in» 

 ftrumcnt employed for that purpofe. On an entire fliell,- 

 or a fragment of one, contained in a glal's veliel, he 

 poured a futlicient quantity of the nitrous acid, confide- 

 rably diluted either with water or I'pirit of wine. After 

 the liquor has diifolved all the earthy part of the fliell, 

 which may be coUefled after precipitation by a fixed or 

 volatile alkali, there remains floa'.ing in it a foft Cub- 

 ftance, confilting of innumerable membranes of a retifonn 

 appearance, and difpofed, in diffecent fliells, in a variety- 

 of pofitious, which conftitutes the anim.al p.irtof it. This, 

 as it has not been atfecled by the (blvent, retains ths 

 exaft figure of the fliell; and, on being viewed throug!* 

 a microlcope, exlilbits fatisf.ictory proofs of a vafcular 

 and organical ftrufture. He (hows that this membranous 

 fubltance is an appendix to the body of the animal, or a- 

 contiiiu.ition of the tendinous fibres ,that compofe the li- 

 gamenls by whicli it is fixed to its fliell ; and that this 

 la(t owes its hardnefs to the earthy particles conveyed 

 through the veffels pf the animal, which fix thenifelves- 

 into, and intrult, as it were, the meflies formed by the 

 reticular filaments of which this membranous luhltance 

 is coiupofed. In the {l\s\lxMed foreelain, in particular, 

 the delicacy of thefe membranes was fo great, that he was 

 obliged to put it into fpifit of wine, to which he had the 

 patience to add a Angle drop of fpirit of nitre day by day, 

 for the (pace of two months ; left the air generated, or 

 let loofe by the ailion of the acid on the earthy (ubitance,. 

 (hould tear the compages of its fine membranous (Iruc- 

 ture, which,, it certiinly would have done, in a mora 

 hafty or lefs gentle diil'olution. The delicate retitulated 

 film, left after this operation, h,ad all the tenuity of a I'pi- 

 der's web ; and accordingly he does not attempt to deli- 

 neate its organization. In other fliells he employed even 

 five or fix months in demonffrating the complicated mem- 

 branous ftruiSlure of this animil iubftance by this kind of 

 chemical anatomy. In general, however, the pioccis does, 

 not require much time. 



Of the many Angular configurations and appearances of 

 the membranous pan of different flitUs, which are defcri- 

 bed in tliis memoir, we Ihail meiitiun only, as a ipeciuien, 

 the curious membranous ftruitureoblerved in the laminaj 

 of mother-of-pearl, and other fliells of the fame kind, af- 

 ter having been expofed to the operation of the author's 

 folvent. Belides the great variety of fixed or permanent 

 colours with wJiicli he (bund the animal filaments of tliel'e 

 flijlls to be adornedOt is known, that the fliell itfelf pre- 

 (ents to the view a fuccefhon of rich and cliangeable co- 

 lours, the produdion of which he eafily explains from the 

 configurations of their membranes. Nature, he obferves, 

 always magnificent in her defigns, but fiugularly frugal 

 in the execution of them, produces thefe brilliant decora- 

 tions at a very fmall expence. The membranous fubftance 

 above-mentioned is plaited and rumpled, as it were, in 

 fuch a manner, that its exterior lamina:, incrulted with 

 their eartliy and l'emi-tran(parent matter, form an infinite 

 4: number 



