SIR，——Theopinionwhich，inyourletterofJanuary24，youarepleasedtoaskofme，onthecomparativemeritsofthedifferentmethodsofclassificationadoptedbydifferentwritersonNaturalHistory，isonewhichIcouldnothavegivensatisfactorily，evenattheearlierperiodatwhichthesubjectwasmorefamiliar；stillless，afteralifeofcontinuedoccupationincivilconcernshassomuchwithdrawnmefromstudiesofthatkind。Ican，therefore，answerbutinaverygeneralway。Andthetextofthisanswerwillbefoundinanobservationinyourletter，where，speakingofnosologicalsystems，yousaythatdiseasehasbeenfoundtobeanunit。Naturehas，intruth，producedunitsonlythroughallherworks。Classes，orders，genera，species，arenotofherwork。Hercreationisofindividuals。Notwoanimalsareexactlyalike；notwoplants，noreventwoleavesorbladesofgrass；notwocrystallizations。Andifwemayventurefromwhatiswithinthecognizanceofsuchorgansasours，toconcludeonthatbeyondtheirpowers，wemustbelievethatnotwoparticlesofmatterareofexactresemblance。Thisinfinitudeofunitsorindividualsbeingfarbeyondthecapacityofourmemory，weareobliged，inaidofthat，todistributethemintomasses，throwingintoeachofthesealltheindividualswhichhaveacertaindegreeofresemblance；tosubdividetheseagainintosmallergroups，accordingtocertainpointsofdissimilitudeobservableinthem，andsoonuntilwehaveformedwhatwecallasystemofclasses，orders，generaandspecies。Indoingthis，wefixarbitrarilyonsuchcharacteristicresemblancesanddifferencesasseemtousmostprominentandinvariableintheseveralsubjects，andmostlikelytotakeastrongholdinourmemories。ThusRayformedoneclassificationonsuchlinesofdivisionasstruckhimmostfavorably；Kleinadoptedanother；Brissonathird，andothernaturalistsotherdesignations，tillLinnaeusappeared。Fortunatelyforscience，heconceivedinthethreekingdomsofnature，modesofclassificationwhichobtainedtheapprobationofthelearnedofallnations。Hissystemwasaccordinglyadoptedbyall，andunitedallinagenerallanguage。Itofferedthethreegreatdesiderata：First，ofaidingthememorytoretainaknowledgeoftheproductionsofnature。Secondly，ofrallyingalltothesamenamesforthesameobjects，sothattheycouldcommunicateunderstandinglyonthem。AndThirdly，ofenablingthem，whenasubjectwasfirstpresented，totraceitbyitscharacteruptotheconventionalnamebywhichitwasagreedtobecalled。Thisclassificationwasindeedliabletotheimperfectionofbringingintothesamegroupindividualswhich，thoughresemblinginthecharacteristicsadoptedbytheauthorforhisclassification，yethavestrongmarksofdissimilitudeinotherrespects。Buttothisobjectioneverymodeofclassificationmustbeliable，becausetheplanofcreationisinscrutabletoourlimitedfaculties。Naturehasnotarrangedherproductionsonasingleanddirectline。Theybranchateverystep，andineverydirection，andhewhoattemptstoreducethemintodepartments，islefttodoitbythelinesofhisownfancy。Theobjectionofbringingtogetherwhataredisparatainnature，liesagainsttheclassificationsofBlumenbachandofCuvier，aswellasthatofLinnaeus，andmustforeverlieagainstall。

　　Perhapsnotinequaldegree；onthisIdonotpronounce。ButneitheristhissoimportantaconsiderationasthatofunitingallnationsunderonelanguageinNaturalHistory。ThishadbeenhappilyeffectedbyLinnaeus，andcanscarcelybehopedforasecondtime。

　　Nothingindeedissodesperateastomakeallmankindagreeingivingupalanguagetheypossess，foronewhichtheyhavetolearn。TheattemptleadsdirectlytotheconfusionofthetonguesofBabel。

　　DisciplesofLinnaeus，ofBlumenbach，andofCuvier，exclusivelypossessingtheirownnomenclatures，cannolongercommunicateintelligiblywithoneanother。Howevermuch，therefore，weareindebtedtoboththesenaturalists，andtoCuvierespecially，forthevaluableadditionstheyhavemadetothesciencesofnature，Icannotsaytheyhaverenderedheraserviceinthisattempttoinnovateinthesettlednomenclatureofherproductions；onthecontrary，Ithinkitwillbeacheckontheprogressofscience，greaterorless，inproportionastheirschemesshallmoreorlessprevail。Theywouldhaverenderedgreaterservicebyholdingfasttothesystemonwhichwehadonceallagreed，andbyinsertingintothatsuchnewgenera，orders，orevenclasses，asnewdiscoveriesshouldcallfor。Theirsystems，too，andespeciallythatofBlumenbach，areliabletotheobjectionofgivingtoomuchintotheprovinceofanatomy。Itmaybesaid，indeed，thatanatomyisapartofnaturalhistory。Inthebroadsenseoftheword，itcertainlyis。Inthatsense，however，itwouldcomprehendallthenaturalsciences，everycreatedthingbeingasubjectofnaturalhistoryinextenso。Butinthesubdivisionsofgeneralscience，ashasbeenobservedintheparticularoneofnaturalhistory，ithasbeennecessarytodrawarbitrarylines，inordertoaccommodateourlimitedviews。Accordingtothese，assoonasthestructureofanynaturalproductionisdestroyedbyart，itceasestobeasubjectofnaturalhistory，andentersintothedomainascribedtochemistry，topharmacy，toanatomy，&c。Linnaeus’methodwasliabletothisobjectionsofarasitrequiredtheaidofanatomicaldissection，asoftheheart，forinstance，toascertaintheplaceofanyanimal，orofachemicalprocessforthatofamineralsubstance。Itwouldcertainlybebettertoadoptasmuchaspossiblesuchexteriorandvisiblecharacteristicsaseverytravelleriscompetenttoobserve，toascertainandtorelate。Butwiththisobjection，lyingbutinasmalldegree，Linnaeus’methodwasreceived，understood，andconventionallysettledamongthelearned，andwasevengettingintocommonuse。Todisturbitthenwasunfortunate。Thenewsystemattemptedinbotany，byJussieu，inmineralogy，byHauiy，aresubjectsofthesameregret，andsoalsotheno-systemofBuffon，thegreatadvocateofindividualisminoppositiontoclassification。HewouldcarryusbacktothedaysandtotheconfusionofAristotleandPliny，giveuptheimprovementsoftwentycenturies，andco-operatewiththeneologistsinrenderingthescienceofonegenerationuselesstothenextbyperpetualchangesofitslanguage。Inbotany，WildenowandPersoonhaveincorporatedintoLinnaeusthenewdiscoveredplants。Idonotknowwhetheranyonehasrenderedusthesameserviceastohisnaturalhistory。Itwouldbeaveryacceptableone。ThematerialsfurnishedbyHumboldt，andthosefromNewHollandparticularly，requiretobedigestedintotheCatholicsystem。Amongthese，theOrnithorhyncusmentionedbyyou，isanamusingexampleoftheanomaliesbywhichnaturesportswithourschemesofclassification。Althoughwithoutmammae，naturalistsareobligedtoplaceitintheclassofmammiferae；andBlumenbach，particularly，arrangesitinhisorderofPalmipedsandtoothlessgenus，withthewalrusandmanatie。InLinnaeus’systemitmightbeinsertedasanewgenusbetweentheanteaterandmanis，intheorderofBruta。Itseems，intruth，tohavestrongerrelationswiththatclassthananyotherintheconstructionoftheheart，itsredandwarmblood，hairyinteguments，inbeingquadrupedandviviparous，andmaywenotsay，inits_toutensemble_，whichBuffonmakeshissoleprincipleofarrangement?Themandible，asyouobserve，woulddrawittowardsthebirds，werenotthischaracteristicoverbalancedbytheweightieronesbeforementioned。ThatoftheCloacaisequivocal，becausealthoughacharacterofbirds，yetsomemammalia，asthebeaverandsloth，havetherectumandurinarypassageterminatingatacommonopening。Itsribsalso，bytheirnumberandstructure，arenearerthoseofthebirdthanofthemammalia。Itispossiblethatfurtheropportunitiesofexaminationmaydiscoverthemammae。ThoseoftheOpossumareasserted，bytheChevalierd’Aboville，fromhisownobservationsonthatanimal，madewhileherewiththeFrencharmy，tobenotdiscoverableuntilpregnancy，andtodisappearassoonastheyoungareweaned。TheDuckbillhasmanyadditionalparticularitieswhichlikenittoothergenera，andsomeentirelypeculiar。Itsdescriptionandhistoryneedsyetfurtherinformation。

　　InwhatIhavesaidonthemethodofclassing，IhavenotatallmeanttoinsinuatethatthatofLinnaeusisintrinsicallypreferabletothoseofBlumenbachandCuvier。IadheretotheLinneanbecauseitissufficientasaground-work，admitsofsupplementaryinsertionsasnewproductionsarediscovered，andmainlybecauseithasgotintosogeneralusethatitwillnotbeeasytodisplaceit，andstilllesstofindanotherwhichshallhavethesamesingularfortuneofobtainingthegeneralconsent。Duringtheattemptweshallbecomeunintelligibletooneanother，andsciencewillbereallyretardedbyeffortstoadvanceitmadebyitsmostfavoritesons。Iamnotmyselfapttobealarmedatinnovationsrecommendedbyreason。Thatdreadbelongstothosewhoseinterestsorprejudicesshrinkfromtheadvanceoftruthandscience。Myreluctanceistogiveupanuniversallanguageofwhichweareinpossession，withoutanassurnaceofgeneralconsenttoreceiveanother。Andthehigherthecharacteroftheauthorsrecommendingit，andthemoreexcellentwhattheyoffer，thegreaterthedangerofproducingschism。

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