Noonedoubtsthat，onthedayandatthehourmentionedbytheAstronomer—Royal，thepeopleofLydiasawthefaceofthesuntotallyobscured。But，thoughweimplicitlybelievethisretrospectiveprophecy，itisincapableofverification。Inthetotalabsenceofhistoricalrecords，itisimpossibleeventoconceiveanymeansofascertainingdirectlywhethertheeclipseofThaleshappenedornot。Allthatcanbesaidis，thattheprospectivepropheciesoftheastronomerarealwaysverified;
andthat，inasmuchashisretrospectivepropheciesaretheresultoffollowingbackwards，theverysamemethodasthatwhichinvariablyleadstoverifiedresults，whenitisworkedforwards，thereisasmuchreasonforplacingfullconfidenceintheoneasintheother。Retrospectiveprophecyisthereforealegitimatefunctionofastronomicalscience;andifitislegitimateforonescienceitislegitimateforall;
thefundamentalaxiomonwhichitrests，theconstancyoftheorderofnature，beingthecommonfoundationofallscientificthought。Indeed，iftherecanbegradesinlegitimacy，certainbranchesofsciencehavetheadvantageoverastronomy，insofarastheirretrospectivepropheciesarenotonlysusceptibleofverification，butaresometimesstrikinglyverified。
Suchascienceexistsinthatapplicationoftheprinciplesofbiologytotheinterpretationoftheanimalandvegetableremainsimbeddedintherockswhichcomposethesurfaceoftheglobe，whichiscalledPalaeontology。
Atnoverydistanttime，thequestionwhethertheseso—called\"fossils，\"werereallytheremainsofanimalsandplantswashotlydisputed。Verylearnedpersonsmaintainedthattheywerenothingofthekind，butasortofconcretion，orcrystallisation，whichhadtakenplacewithinthestoneinwhichtheyarefound;andwhichsimulatedtheformsofanimalandvegetablelife，justasfrostonawindow—paneimitatesvegetation。Atthepresentday，itwouldprobablybeimpossibletofindanysaneadvocateofthisopinion;andthefactisrathersurprising，thatamongthepeoplefromwhomthecircle—
squarers，perpetual—motioners，flat—earthedmenandthelike，arerecruited，tosaynothingoftable—turnersandspirit—
rappers，somebodyhasnotperceivedtheeasyavenuetononsensicalnotorietyopentoanyonewhowilltakeupthegoodolddoctrine，thatfossilsarealllususnaturae。
Thepositionwouldbeimpregnable，inasmuchasitisquiteimpossibletoprovethecontrary。Ifamanchoosetomaintainthatafossiloystershell，inspiteofitscorrespondence，downtoeveryminutestparticular，withthatofanoysterfreshtakenoutofthesea，wasnevertenantedbyalivingoyster，butisamineralconcretion，thereisnodemonstratinghiserror。
Allthatcanbedoneistoshowhimthat，byaparityofreasoning，heisboundtoadmitthataheapofoystershellsoutsideafishmonger’sdoormayalsobe\"sportsofnature，\"andthatamuttonboneinadust—binmayhavehadthelikeorigin。
Andwhenyoucannotprovethatpeoplearewrong，butonlythattheyareabsurd，thebestcourseistoletthemalone。
Thewholefabricofpalaeontology，infact，fallstothegroundunlessweadmitthevalidityofZadig’sgreatprinciple，thatlikeeffectsimplylikecauses，andthattheprocessofreasoningfromashell，oratooth，orabone，tothenatureoftheanimaltowhichitbelonged，restsabsolutelyontheassumptionthatthelikenessofthisshell，ortooth，orbone，tothatofsomeanimalwithwhichwearealreadyacquainted，issuchthatwearejustifiedininferringacorrespondingdegreeoflikenessintherestofthetwoorganisms。Itisonthisverysimpleprinciple，andnotuponimaginarylawsofphysiologicalcorrelation，aboutwhich，inmostcases，weknownothingwhatever，thattheso—calledrestorationsofthepalaeontologistarebased。
Abundantillustrationsofthistruthwilloccurtoeveryonewhoisfamiliarwithpalaeontology;noneismoresuitablethanthecaseoftheso—calledBelemnites。Intheearlydaysofthestudyoffossils，thisnamewasgiventocertainelongatedstonybodies，endingatoneextremityinaconicalpoint，andtruncatedattheother，whichwerecommonlyreputedtobethunderbolts，andassuchtohavedescendedfromthesky。
TheyarecommonenoughinsomepartsofEngland;and，intheconditioninwhichtheyareordinarilyfound，itmightbedifficulttogivesatisfactoryreasonsfordenyingthemtobemerelymineralbodies。
Theyappear，infact，toconsistofnothingbutconcentriclayersofcarbonateoflime，disposedinsubcrystallinefibres，orprisms，perpendiculartothelayers。AmongagreatnumberofspecimensoftheseBelemnites，however，itwassoonobservedthatsomeshowedaconicalcavityatthebluntend;and，instillbetterpreservedspecimens，thiscavityappearedtobedividedintochambersbydelicatesaucer—shapedpartitions，situatedatregularintervalsoneabovetheother。Nowthereisnomineralbodywhichpresentsanystructurecomparabletothis，andtheconclusionsuggesteditselfthattheBelemnitesmustbetheeffectsofcausesotherthanthosewhichareatworkininorganicnature。Oncloseexamination，thesaucer—shapedpartitionswereprovedtobeallperforatedatonepoint，andtheperforationsbeingsituatedexactlyinthesameline，thechamberswereseentobetraversedbyacanal，orsiphuncle，whichthusconnectedthesmallestoraphicalchamberwiththelargest。Thereisnothinglikethisinthevegetableworld;butanexactlycorrespondingstructureismetwithintheshellsoftwokindsofexistinganimals，thepearlyNautilusandtheSpirula，andonlyinthem。Theseanimalsbelongtothesamedivision——theCephalopoda——asthecuttle—fish，thesquid，andtheoctopus。Buttheyaretheonlyexistingmembersofthegroupwhichpossesschambered，siphunculatedshells;anditisutterlyimpossibletotraceanyphysiologicalconnectionbetweentheverypeculiarstructuralcharactersofacephalopodandthepresenceofachamberedshell。Infact，thesquidhas，insteadofanysuchshell，ahorny\"pen，\"thecuttlefishhastheso—called\"cuttle—bone，\"andtheoctopushasnoshell，or，atmost，amererudimentofone。
Nevertheless，seeingthatthereisnothinginnatureatalllikethechamberedshelloftheBelemnite，excepttheshellsoftheNautilusandoftheSpirula，itwaslegitimatetoprophesythattheanimalfromwhichthefossilproceededmusthavebelongedtothegroupoftheCephalopoda。
NautilusandSpirulaarebothveryrareanimals，buttheprogressofinvestigationbroughttolightthesingularfact，that，thougheachhasthecharacteristiccephalopodousorganisation，itisverydifferentfromtheother。TheshellofNautilusisexternal，thatofSpirulainternal;
Nautilushasfourgills，Spirulatwo;
Nautilushasmultitudinoustentacles，Spirulahasonlytenarmsbesetwithhorny—rimmedsuckers;Spirula，
likethesquidsandcuttle—fishes，whichitcloselyresembles，hasabagofinkwhichitsquirtsouttocoveritsretreatwhenalarmed;Nautilushasnone。
NoamountofphysiologicalreasoningcouldenableanyonetosaywhethertheanimalwhichfabricatedtheBelemnitewasmorelikeNautilus，ormorelikeSpirula。ButtheaccidentaldiscoveryofBelemnitesindueconnectionwithblackelongatedmasseswhichwere:certainlyfossilisedink—bags，inasmuchastheinkcouldbegroundupandusedforpaintingaswellasifitwererecentsepia，settledthequestion;anditbecameperfectlysafetoprophesythatthecreaturewhichfabricatedtheBelemnitewasatwo—gilledcephalopodwithsuckersonitsarms，andwithalltheotheressentialfeaturesofourlivingsquids，cuttle—fishes，andSpirulae。Thepalaeontologistwas，bythistime，abletospeakasconfidentlyabouttheanimaloftheBelemnite，asZadigwasrespectingthequeen’sspaniel。
Hecouldgiveaveryfairdescriptionofitsexternalappearance，andevenenterprettyfullyintothedetailsofitsinternalorganisation，andyetcoulddeclarethatneitherhe，noranyoneelse，hadeverseenone。Andasthequeen’sspanielwasfound，sohappilyhastheanimaloftheBelemnite;afewexceptionallypreservedspecimenshavebeendiscovered，whichcompletelyverifytheretrospectiveprophecyofthosewhointerpretedthefactsofthecasebydueapplicationofthemethodofZadig。
TheseBelemnitesflourishedinprodigiousabundanceintheseasofthemesozoic，orsecondary，ageoftheworld’sgeologicalhistory;butnotraceofthemhasbeenfoundinanyofthetertiarydeposits，andtheyappeartohavediedouttowardsthecloseofthemesozoicepoch。ThemethodofZadig，therefore，appliesinfullforcetotheeventsofaperiodwhichisimmeasurablyremote，whichlongprecededtheoriginofthemostconspicuousmountainmassesofthepresentworld，andthedeposition，atthebottomoftheocean，oftherockswhichformthegreaterpartofthesoilofourpresentcontinents。
TheEuphratesitself，atthemouthofwhichOanneslanded，isathingofyesterdaycomparedwithaBelemnite;andeventheliberalchronologyofmagiancosmogonyfixesthebeginningoftheworldonlyatatimewhenotherapplicationsofZadig’smethodaffordconvincingevidencethat，couldwehavebeentheretosee，thingswouldhavelookedverymuchastheydonow。
Trulythemagiwerewiseintheirgeneration;theyforesawrightlythatthispestilentapplicationoftheprinciplesofcommonsense，inauguratedbyZadig，wouldbetheirruin。
ButitmaybesaidthatthemethodofZadig，whichissimplereasoningfromanalogy，doesnotaccountforthemoststrikingfeatsofmodernpalaeontology——thereconstructionofentireanimalsfromatoothorperhapsafragmentofabone;anditmaybejustlyurgedthatCuvier，thegreatmasterofthiskindofinvestigation，gaveaverydifferentaccountoftheprocesswhichyieldedsuchremarkableresults。
Cuvierisnotthefirstmanofabilitywhohasfailedtomakehisownmentalprocessescleartohimself，andhewillnotbethelast。Themattercanbeeasilytested。Searchtheeightvolumesofthe\"RecherchessurlesOssemensFossiles\"fromcovertocover，andnothingbuttheapplicationofthemethodofZadigwillbefoundintheargumentsbywhichafragmentofaskeletonismadetorevealthecharactersoftheanimaltowhichitbelonged。
Thereisonewell—knowncasewhichmayrepresentall。ItisanexcellentillustrationofCuvier’ssagacity，andheevidentlytakessomeprideintellinghisstoryaboutit。AsplitslabofstonearrivedfromthequarriesofMontmartre，thetwohalvesofwhichcontainedthegreaterpartoftheskeletonofasmallanimal。Oncarefulexaminationsofthecharactersoftheteethandofthelowerjaw，whichhappenedtobeexposed，Cuvierassuredhimselfthattheypresentedsuchaverycloseresemblancetothecorrespondingpartsinthelivingopossumsthatheatonceassignedthefossiltothatgenus。
Nowtheopossumsareunlikemostmammalsinthattheypossesstwobonesattachedtotheforepartofthepelvis，whicharecommonlycalled\"marsupialbones。\"Thenameisamisnomer，originallyconferredbecauseitwasthoughtthattheseboneshavesomethingtodowiththesupportofthepouch，ormarsupium，withwhichsome，butnotall，oftheopossumsareprovided。Asamatteroffact，theyhavenothingtodowiththesupportofthepouch，andtheyexistasmuchinthoseopossumswhichhavenopouchesasinthosewhichpossessthem。Intruth，nooneknowswhattheuseofthesebonesmaybe，norhasanyvalidtheoryoftheirphysiologicalimportyetbeensuggested。
Andifwehavenoknowledgeofthephysiologicalimportanceofthebonesthemselves，itisobviouslyabsurdtopretendthatweareabletogivephysiologicalreasonswhythepresenceofthesebonesisassociatedwithcertainpeculiaritiesoftheteethandofthejaws。Ifanyoneknowswhyfourmolarteethandaninflectedangleofthejawareverygenerallyfoundalongwithmarsupialbones，hehasnotyetcommunicatedthatknowledgetotheworld。
If，however，Zadigwasrightinconcludingfromthelikenessofthehoof—printswhichheobservedtobeahorse’sthatthecreaturewhichmadethemhadataillikethatofahorse，Cuvier，seeingthattheteethandjawofhisfossilwerejustlikethoseofanopossum，hadthesamerighttoconcludethatthepelviswouldalsobelikeanopossum’s;andsostrongwashisconvictionthatthisretrospectiveprophecy，aboutananimalwhichhehadneverseenbefore，andwhichhadbeendeadandburiedformillionsofyears，wouldbeverified，thathewenttoworkupontheslabwhichcontainedthepelvisinconfidentexpectationoffindingandlayingbarethe\"marsupialbones，\"tothesatisfactionofsomepersonswhomhehadinvitedtowitnesstheirdisinterment。Ashesays:——\"Cetteoperationsefitenpresencedequelquespersonnesaquij’enavaisannonced’avanceleresultat，dansl’intentiondeleurprouverparlefaitlajusticedenostheorieszoologiques;puisquelevraicachetd’unetheorieestsanscontreditlafacultequ’elledonnedeprevoirlesphenomenes。\"
Inthe\"OssemensFossiles\"Cuvierleaveshispaperjustasitfirstappearedinthe\"AnnalesduMuseum，\"as\"acuriousmonumentoftheforceofzoologicallawsandoftheusewhichmaybemadeofthem。\"
Zoologicallawstruly，butnotphysiologicallaws。Ifoneseesalivedog’shead，itisextremelyprobablethatadog’stailisnotfaroff，thoughnobodycansaywhythatsortofheadandthatsortoftailgotogether;whatphysiologicalconnectionthereisbetweenthetwo。So，inthecaseoftheMontmartrefossil，Cuvier，findingathoroughopossum’shead，concludedthatthepelvisalsowouldbelikeanopossum’s。But，mostassuredly，themostadvancedphysiologistofthepresentdaycouldthrownolightonthequestionwhytheseareassociated，norcouldpretendtoaffirmthattheexistenceoftheoneisnecessarilyconnectedwiththatoftheother。Infact，haditsohappenedthatthepelvisofthefossilhadbeenoriginallyexposed，whiletheheadlayhidden，thepresenceofthe\"marsupialbones，\"thoughverylikeanopossum’s，wouldbynomeanshavewarrantedthepredictionthattheskullwouldturnouttobethatoftheopossum。Itmightjustaswellhavebeenlikethatofsomeothermarsupial;orevenlikethatofthetotallydifferentgroupofMonotremes，ofwhichtheonlylivingrepresentativesaretheEchidnaandtheOrnithorhynchus。
Forallpracticalpurposes，however，theempiricallawsofco—
ordinationofstructures，whichareembodiedinthegeneralisationsofmorphology，maybeconfidentlytrusted，ifemployedwithduecaution，toleadtoajustinterpretationoffossilremains;or，inotherwords，wemaylookfortheverificationoftheretrospectiveprophecieswhicharebaseduponthem。
Andifthisbethecase，thelateadvanceswhichhavebeenmadeinpalaeontologicaldiscoveryopenoutanewfieldforsuchprophecies。Forithasbeenascertainedwithrespecttomanygroupsofanimals，that，aswetracethembackintime，theirancestorsgraduallyceasetoexhibitthosespecialmodificationswhichatpresentcharacterisethetype，andmorenearlyembodythegeneralplanofthegrouptowhichtheybelong。
Thus，inthewell—knowncaseofthehorse，thetoeswhicharesuppressedinthelivinghorsearefoundtobemoreandmorecompleteintheoldermembersofthegroup，until，atthebottomoftheTertiaryseriesofAmerica，wefindanequineanimalwhichhasfourtoesinfrontandthreebehind。NoremainsofthehorsetribeareatpresentknownfromanyMesozoicdeposit。
Yetwhocandoubtthat，wheneverasufficientlyextensiveseriesoflacustrineandfluviatilebedsofthatagebecomesknown，thelineagewhichhasbeentracedthusfarwillbecontinuedbyequinequadrupedswithanincreasingnumberofdigits，untilthehorsetypemergesinthefive—toedformtowardswhichthesegradationspoint？
Buttheargumentwhichholdsgoodforthehorse，holdsgood，notonlyforallmammals，butforthewholeanimalworld。Andasthestudyofthepedigrees，orlinesofevolution，towhich，atpresent，wehaveaccess，bringstolight，asitassuredlywilldo，thelawsofthatprocess，weshallbeabletoreasonfromthefactswithwhichthegeologicalrecordfurnishesustothosewhichhavehithertoremained，andmanyofwhich，perhaps，mayforeverremain，hidden。Thesamemethodofreasoningwhichenablesus，whenfurnishedwithafragmentofanextinctanimal，toprophesythecharacterwhichthewholeorganismexhibited，will，soonerorlater，enableus，whenweknowafewofthelatertermsofagenealogicalseries，topredictthenatureoftheearlierterms。
Innoverydistantfuture，themethodofZadig，appliedtoagreaterbodyoffactsthanthepresentgenerationisfortunateenoughtohandle，willenablethebiologisttoreconstructtheschemeoflifefromitsbeginning，andtospeakasconfidentlyofthecharacteroflongextinctbeings，notraceofwhichhasbeenpreserved，asZadigdidofthequeen’sspanielandtheking’shorse。LetushopethattheymaybebetterrewardedfortheirtoilandtheirsagacitythanwastheBabylonianphilosopher;forperhaps，bythattime，themagialsomaybereckonedamongthemembersofaforgottenFauna，extinguishedinthestruggleforexistenceagainsttheirgreatrival，commonsense。
FOOTNOTES
（1）\"Discourssurlesrevolutionsdelasurfaceduglobe。\"
RecherchessurlesOssemensFossiles，Ed。iv，t。i。p。185。]
（2）\"OntheEclipsesofAgathocles，Thales，andXerxes，\"
PhilosophicalTransactions，vol。cxliii。