Ofthegreatthinkersofthenineteenthcentury，ThomasHenryHuxley，sonofanEalingschoolmaster，wasundoubtedlythemostnoteworthy。Hisresearchesinbiology，hiscontributionstoscientificcontroversy，hispungentcriticismsofconventionalbeliefsandthoughtshaveprobablyhadgreaterinfluencethantheworkofanyotherEnglishscientist。Andyethewasaself-madeintellectualist。Inspiteofthefactthathisfatherwasaschoolmasterhepassedthroughnoregularcourseofeducation。Ihad，hesaid，twoyearsofapandemoniumofaschool(betweeneightandten)andafterthatneitherhelpnorsympathyinanyintellectualdirectiontillIreachedmanhood。WhenhewastwelveacravingforreadingfoundsatisfactioninHutton’sGeology，andwhenfifteeninHamilton’sLogic。

AtseventeenHuxleyenteredasastudentatCharingCrossHospital，andthreeyearslaterhewasM。B。andthepossessorofthegoldmedalforanatomyandphysiology。AnappointmentassurgeoninthenavyprovedtobetheentrytoHuxley’sgreatscientificcareer，forhewasgazettedtotheRattlesnake，commissionedforsurveyingworkinTorresStraits。Hewasattractedbytheteemingsurfacelifeoftropicalseasandhisstudyofitwasthecommencementofthatrevolutioninscientificknowledgeultimatelybroughtaboutbyhisresearches。

ThomasHenryHuxleywasbornatEalingonMay4，1825，anddiedatEastbourneJune29，1895。

LECTURESANDESSAYSBYT。H。HUXLEY

ONOURKNOWLEDGEOFTHECAUSESOFTHEPHENOMENAOFORGANICNATURE

NOTICETOTHEFIRSTEDITION。

ThePublisheroftheseinterestingLectures，havingmadeanarrangementfortheirpublicationwithMr。J。A。Mays，theReporter，begstoappendthefollowingnotefromProfessorHuxley：——

Mr。J。AldousMays，whoistakingshorthandnotesofmy’LecturestoWorkingMen，’hasaskedmetoallowhim，onhisownaccount，toprintthoseNotesfortheuseofmyaudience。Iwillinglyaccedetothisrequest，ontheunderstandingthatanoticeisprefixedtotheeffectthatIhavenoleisuretorevisetheLectures，ortomakealterationsinthem，beyondthecorrectionofanyimportanterrorinamatteroffact。

THEPRESENTCONDITIONOFORGANICNATURE。

WhenitwasmydutytoconsiderwhatsubjectIwouldselectforthesixlectures[*ToWorkingMen，attheMuseumofPracticalGeology，1863。]

whichIshallnowhavethepleasureofdeliveringtoyou，itoccurredtomethatIcouldnotdobetterthanendeavourtoputbeforeyouinatruelight，orinwhatImightperhapswithmoremodestycall，thatwhichIconceivemyselftobethetruelight，thepositionofabookwhichhasbeenmorepraisedandmoreabused，perhaps，thananybookwhichhasappearedforsomeyears——ImeanMr。Darwin’sworkontheOriginofSpecies。Thatwork，Idoubtnot，manyofyouhaveread。

forIknowtheinquiringspiritwhichisrifeamongyou。Atanyrate，allofyouwillhaveheardofit，——somebyonekindofreportandsomebyanotherkindofreport。theattentionofallandthecuriosityofallhavebeenprobablymoreorlessexcitedonthesubjectofthatwork。AllIcando，andallIshallattempttodo，istoputbeforeyouthatkindofjudgmentwhichhasbeenformedbyaman，who，ofcourse，isliabletojudgeerroneously。but，atanyrate，ofonewhosebusinessandprofessionitistoformjudgmentsuponquestionsofthisnature。

Andhere，asitwillalwayshappenwhendealingwithanextensivesubject，thegreaterpartofmycourse——if，indeed，sosmallanumberoflecturescanbeproperlycalledacourse——mustbedevotedtopreliminarymatters，orrathertoastatementofthosefactsandofthoseprincipleswhichtheworkitselfdwellsupon，andbringsmoreorlessdirectlybeforeus。Ihavenorighttosupposethatalloranyofyouarenaturalists。andevenifyouwere，themisconceptionsandmisunderstandingsprevalentevenamongnaturalistsonthesematterswouldmakeitdesirablethatIshouldtakethecourseInowproposetotake，——thatIshouldstartfromthebeginning，——thatIshouldendeavourtopointoutwhatistheexistingstateoftheorganicworld，——thatI

shouldpointoutitspastcondition，——thatIshouldstatewhatistheprecisenatureoftheundertakingwhichMr。Darwinhastakeninhand。

thatIshouldendeavourtoshowyouwhataretheonlymethodsbywhichthatundertakingcanbebroughttoanissue，andtopointouttoyouhowfartheauthoroftheworkinquestionhassatisfiedthoseconditions，howfarhehasnotsatisfiedthem，howfartheyaresatisfiablebyman，andhowfartheyarenotsatisfiablebyman。

To-night，intakingupthefirstpartofthisquestion，Ishallendeavourtoputbeforeyouasortofbroadnotionofourknowledgeoftheconditionofthelivingworld。Therearemanywaysofdoingthis。

Imightdealwithitpictoriallyandgraphically。FollowingtheexampleofHumboldtinhisAspectsofNature，Imightendeavourtopointouttheinfinitevarietyoforganiclifeineverymodeofitsexistence，withreferencetothevariationsofclimateandthelike。

andsuchanattemptwouldbefraughtwithinteresttousall。butconsideringthesubjectbeforeus，suchacoursewouldnotbethatbestcalculatedtoassistus。Inanargumentofthiskindwemustgofurtheranddigdeeperintothematter。wemustendeavourtolookintothefoundationsoflivingNature，ifImaysosay，anddiscovertheprinciplesinvolvedinsomeofhermostsecretoperations。Ipropose，therefore，inthefirstplace，totakesomeordinaryanimalwithwhichyouareallfamiliar，and，byeasilycomprehensibleandobviousexamplesdrawnfromit，toshowwhatarethekindofproblemswhichlivingbeingsingenerallaybeforeus。andIshallthenshowyouthatthesameproblemsarelaidopentousbyallkindsoflivingbeings。

Butfirst，letmesayinwhatsenseIhaveusedthewordsorganicnature。Inspeakingofthecauseswhichleadtoourpresentknowledgeoforganicnature，Ihaveuseditalmostasanequivalentofthewordliving，andforthisreason，——thatinalmostalllivingbeingsyoucandistinguishseveraldistinctportionssetaparttodoparticularthingsandworkinaparticularway。Thesearetermedorgans，andthewholetogetheriscalledorganic。Andasitisuniversallycharacteristicofthem，thistermorganichasbeenveryconvenientlyemployedtodenotethewholeoflivingnature，——thewholeoftheplantworld，andthewholeoftheanimalworld。

Fewanimalscanbemorefamiliartoyouthanthatwhoseskeletonisshownonourdiagram。YouneednotbotheryourselveswiththisEquuscaballuswrittenunderit。thatisonlytheLatinnameofit，anddoesnotmakeitanybetter。ItsimplymeansthecommonHorse。SupposewewishtounderstandallabouttheHorse。Ourfirstobjectmustbetostudythestructureoftheanimal。Thewholeofhisbodyisinclosedwithinahide，askincoveredwithhair。andifthathideorskinbetakenoff，wefindagreatmassofflesh，orwhatistechnicallycalledmuscle，beingthesubstancewhichbyitspowerofcontractionenablestheanimaltomove。Thesemusclesmovethehardpartsoneupontheother，andsogivethatstrengthandpowerofmotionwhichrenderstheHorsesousefultousintheperformanceofthoseservicesinwhichweemployhim。

Andthen，onseparatingandremovingthewholeofthisskinandflesh，youhaveagreatseriesofbones，hardstructures，boundtogetherwithligaments，andformingtheskeletonwhichisrepresentedhere。

[FIGURE1。(Sectionthroughahorse。)

FIGURE2。(Sectionthroughacell。)]

Inthatskeletonthereareanumberofpartstoberecognized。Thelongseriesofbones，beginningfromtheskullandendinginthetail，iscalledthespine，andthoseinfrontaretheribs。andthentherearetwopairsoflimbs，onebeforeandonebehind。andtherearewhatweallknowasthefore-legsandthehind-legs。Ifwepursueourresearchesintotheinteriorofthisanimal，wefindwithintheframeworkoftheskeletonagreatcavity，orrather，Ishouldsay，twogreatcavities，——onecavitybeginningintheskullandrunningthroughtheneck-bones，alongthespine，andendinginthetail，containingthebrainandthespinalmarrow，whichareextremelyimportantorgans。Thesecondgreatcavity，commencingwiththemouth，containsthegullet，thestomach，thelongintestine，andalltherestofthoseinternalapparatuswhichareessentialfordigestion。andtheninthesamegreatcavity，therearelodgedtheheartandallthegreatvesselsgoingfromit。and，besidesthat，theorgansofrespiration——thelungs：andthenthekidneys，andtheorgansofreproduction，andsoon。Letusnowendeavourtoreducethisnotionofahorsethatwenowhave，tosomesuchkindofsimpleexpressionascanbeatonce，andwithoutdifficulty，retainedinthemind，apartfromallminordetails。IfI

makeatransversesection，thatis，ifIweretosawadeadhorseacross，Ishouldfindthat，ifIleftoutthedetails，andsupposingI

tookmysectionthroughtheanteriorregion，andthroughthefore-limbs，Ishouldhaveherethiskindofsectionofthebody(Fig。

1)。Herewouldbetheupperpartoftheanimal——thatgreatmassofbonesthatwespokeofasthespine(a，Fig。1)。HereIshouldhavethealimentarycanal(b，Fig。1)。HereIshouldhavetheheart(c，Fig。1)。andthenyousee，therewouldbeakindofdoubletube，thewholebeinginclosedwithinthehide。thespinalmarrowwouldbeplacedintheuppertube(a，Fig。1)，andinthelowertube(dd，Fig。1)，therewouldbethealimentarycanal(b)，andtheheart(c)。andhereI

shallhavethelegsproceedingfromeachside。Forsimplicity’ssake，Irepresentthemmerelyasstumps(ee，Fig。1)。Nowthatisahorse——asmathematicianswouldsay——reducedtoitsmostsimpleexpression。Carrythatinyourminds，ifyouplease，asasimplifiedideaofthestructureoftheHorse。TheconsiderationswhichIhavenowputbeforeyoubelongtowhatwetechnicallycallthe’Anatomy’oftheHorse。Now，supposewegotoworkupontheseseveralparts，——fleshandhair，andskinandbone，andlayopenthesevariousorganswithourscalpels，andexaminethembymeansofourmagnifying-glasses，andseewhatwecanmakeofthem。Weshallfindthatthefleshismadeupofbundlesofstrongfibres。Thebrainandnerves，too，weshallfind，aremadeupoffibres，andthesequeer-lookingthingsthatarecalledganglioniccorpuscles。Ifwetakeasliceoftheboneandexamineit，weshallfindthatitisverylikethisdiagramofasectionoftheboneofanostrich，thoughdiffering，ofcourse，insomedetails。andifwetakeanypartwhatsoeverofthetissue，andexamineit，weshallfinditallhasaminutestructure，visibleonlyunderthemicroscope。

Allthesepartsconstitutemicroscopicanatomyor’Histology。’Thesepartsareconstantlybeingchanged。everypartisconstantlygrowing，decaying，andbeingreplacedduringthelifeoftheanimal。Thetissueisconstantlyreplacedbynewmaterial。andifyougobacktotheyoungstateofthetissueinthecaseofmuscle，orinthecaseofskin，oranyoftheorgansIhavementioned，youwillfindthattheyallcomeunderthesamecondition。Everyoneofthesemicroscopicfilamentsandfibres(Inowspeakmerelyofthegeneralcharacterofthewholeprocess)——everyoneoftheseparts——couldbetraceddowntosomemodificationofatissuewhichcanbereadilydividedintolittleparticlesoffleshymatter，ofthatsubstancewhichiscomposedofthechemicalelements，carbon，hydrogen，oxygen，andnitrogen，havingsuchashapeasthis(Fig。2)。Theseparticles，intowhichallprimitivetissuesbreakup，arecalledcells。IfIweretomakeasectionofapieceoftheskinofmyhand，Ishouldfindthatitwasmadeupofthesecells。IfIexaminethefibreswhichformthevariousorgansofalllivinganimals，Ishouldfindthatallofthem，atonetimeorother，hadbeenformedoutofasubstanceconsistingofsimilarelements。sothatyousee，justaswereducedthewholebodyinthegrosstothatsortofsimpleexpressiongiveninFig。1，sowemayreducethewholeofthemicroscopicstructuralelementstoaformofevengreatersimplicity。justastheplanofthewholebodymaybesorepresentedinasense(Fig。1)，sotheprimarystructureofeverytissuemayberepresentedbyamassofcells(Fig。2)。

Havingthus，inthissortofgeneralway，sketchedtoyouwhatImaycall，perhaps，thearchitectureofthebodyoftheHorse(whatwetermtechnicallyitsMorphology)，Imustnowturntoanotheraspect。A

horseisnotameredeadstructure：itisanactive，living，workingmachine。Hithertowehave，asitwere，beenlookingatasteam-enginewiththefiresout，andnothingintheboiler。butthebodyofthelivinganimalisabeautifully-formedactivemachine，andeveryparthasitsdifferentworktodointheworkingofthatmachine，whichiswhatwecallitslife。TheHorse，ifyouseehimafterhisday’sworkisdone，iscroppingthegrassinthefields，asitmaybe，ormunchingtheoatsinhisstable。Whatishedoing？Hisjawsareworkingasamill——andaverycomplexmilltoo——grindingthecorn，orcrushingthegrasstoapulp。Assoonasthatoperationhastakenplace，thefoodispasseddowntothestomach，andthereitismixedwiththechemicalfluidcalledthegastricjuice，asubstancewhichhasthepeculiarpropertyofmakingsolubleanddissolvingoutthenutritiousmatterinthegrass，andleavingbehindthosepartswhicharenotnutritious。sothatyouhave，first，themill，thenasortofchemicaldigester。andthenthefood，thuspartiallydissolved，iscarriedbackbythemuscularcontractionsoftheintestinesintothehinderpartsofthebody，whilethesolubleportionsaretakenupintotheblood。Thebloodiscontainedinavastsystemofpipes，spreadingthroughthewholebody，connectedwithaforcepump，——theheart，——which，byitspositionandbythecontractionsofitsvalves，keepsthebloodconstantlycirculatinginonedirection，neverallowingittorest。andthen，bymeansofthiscirculationoftheblood，ladenasitiswiththeproductsofdigestion，theskin，theflesh，thehair，andeveryotherpartofthebody，drawsfromitthatwhichitwants，andeveryoneoftheseorgansderivesthosematerialswhicharenecessarytoenableittodoitswork。

Theactionofeachoftheseorgans，theperformanceofeachofthesevariousduties，involveintheiroperationacontinualabsorptionofthemattersnecessaryfortheirsupport，fromtheblood，andaconstantformationofwasteproducts，whicharereturnedtotheblood，andconveyedbyittothelungsandthekidneys，whichareorgansthathaveallottedtothemtheofficeofextracting，separating，andgettingridofthesewasteproducts。andthusthegeneralnourishment，labour，andrepairofthewholemachineiskeptupwithorderandregularity。Butnotonlyisitamachinewhichfeedsandappropriatestoitsownsupportthenourishmentnecessarytoitsexistence——itisanengineforlocomotivepurposes。TheHorsedesirestogofromoneplacetoanother。andtoenableittodothis，ithasthosestrongcontractilebundlesofmusclesattachedtothebonesofitslimbs，whichareputinmotionbymeansofasortoftelegraphicapparatusformedbythebrainandthegreatspinalcordrunningthroughthespineorbackbone。andtothisspinalcordareattachedanumberoffibrestermednerves，whichproceedtoallpartsofthestructure。Bymeansofthesetheeyes，nose，tongue，andskin——alltheorgansofperception——transmitimpressionsorsensationstothebrain，whichactsasasortofgreatcentraltelegraph-office，receivingimpressionsandsendingmessagestoallpartsofthebody，andputtinginmotionthemusclesnecessarytoaccomplishanymovementthatmaybedesired。Sothatyouhavehereanextremelycomplexandbeautifully-proportionedmachine，withallitspartsworkingharmoniouslytogethertowardsonecommonobject——thepreservationofthelifeoftheanimal。

Now，notethis：theHorsemakesupitswastebyfeeding，anditsfoodisgrassoroats，orperhapsothervegetableproducts。therefore，inthelongrun，thesourceofallthiscomplexmachineryliesinthevegetablekingdom。Butwheredoesthegrass，ortheoat，oranyotherplant，obtainthisnourishingfood-producingmaterial？Atfirstitisalittleseed，whichsoonbeginstodrawintoitselffromtheearthandthesurroundingairmatterswhichinthemselvescontainnovitalpropertieswhatever。itabsorbsintoitsownsubstancewater，aninorganicbody。itdrawsintoitssubstancecarbonicacid，aninorganicmatter。andammonia，anotherinorganicmatter，foundintheair。andthen，bysomewonderfulchemicalprocess，thedetailsofwhichchemistsdonotyetunderstand，thoughtheyarenearforeshadowingthem，itcombinesthemintoonesubstance，whichisknowntousas’Protein，’acomplexcompoundofcarbon，hydrogen，oxygen，andnitrogen，whichalonepossessesthepropertyofmanifestingvitalityandofpermanentlysupportinganimallife。Sothat，yousee，thewasteproductsoftheanimaleconomy，theeffetematerialswhicharecontinuallybeingthrownoffbyalllivingbeings，intheformoforganicmatters，areconstantlyreplacedbysuppliesofthenecessaryrepairingandrebuildingmaterialsdrawnfromtheplants，whichintheirturnmanufacturethem，sotospeak，byamysteriouscombinationofthosesameinorganicmaterials。

LetustraceoutthehistoryoftheHorseinanotherdirection。Afteracertaintime，astheresultofsicknessordisease，theeffectofaccident，ortheconsequenceofoldage，soonerorlater，theanimaldies。Themultitudinousoperationsofthisbeautifulmechanismflagintheirperformance，theHorselosesitsvigour，andafterpassingthroughthecuriousseriesofchangescomprisedinitsformationandpreservation，itfinallydecays，andendsitslifebygoingbackintothatinorganicworldfromwhichallbutaninappreciablefractionofitssubstancewasderived。Itsbonesbecomemerecarbonateandphosphateoflime。thematterofitsflesh，andofitsotherparts，becomes，inthelongrun，convertedintocarbonicacid，intowater，andintoammonia。Youwillnow，perhaps，understandthecuriousrelationoftheanimalwiththeplant，oftheorganicwiththeinorganicworld，whichisshowninthisdiagram(Fig。3)。

[FIGURE3。(DiagramshowingmaterialrelationshipoftheVegetable，AnimalandInorganicWorlds。)]

Theplantgatherstheseinorganicmaterialstogetherandmakesthemupintoitsownsubstance。Theanimaleatstheplantandappropriatesthenutritiousportionstoitsownsustenance，rejectsandgetsridoftheuselessmatters。and，finally，theanimalitselfdies，anditswholebodyisdecomposedandreturnedintotheinorganicworld。Thereisthusaconstantcirculationfromonetotheother，acontinualformationoforganiclifefrominorganicmatters，andasconstantareturnofthematteroflivingbodiestotheinorganicworld。sothatthematerialsofwhichourbodiesarecomposedarelargely，inallprobability，thesubstanceswhichconstitutedthematteroflongextinctcreations，butwhichhaveintheintervalconstitutedapartoftheinorganicworld。

Thuswecometotheconclusion，strangeatfirstsight，thattheMATTER

constitutingthelivingworldisidenticalwiththatwhichformstheinorganicworld。Andnotlesstrueisitthat，remarkableasarethepowersor，inotherwords，asaretheFORCESwhichareexertedbylivingbeings，yetalltheseforcesareeitheridenticalwiththosewhichexistintheinorganicworld，ortheyareconvertibleintothem。

Imeaninjustthesamesenseastheresearchesofphysicalphilosophershaveshownthatheatisconvertibleintoelectricity，thatelectricityisconvertibleintomagnetism，magnetismintomechanicalforceorchemicalforce，andanyoneofthemwiththeother，eachbeingmeasurableintermsoftheother，——evenso，Isay，thatgreatlawisapplicabletothelivingworld。Considerwhyistheskeletonofthishorsecapableofsupportingthemassesoffleshandthevariousorgansformingthelivingbody，unlessitisbecauseoftheactionofthesameforcesofcohesionwhichcombinestogethertheparticlesofmattercomposingthispieceofchalk？Whatisthereinthemuscularcontractilepoweroftheanimalbuttheforcewhichisexpressible，andwhichisinacertainsenseconvertible，intotheforceofgravitywhichitovercomes？Or，ifyougotomorehiddenprocesses，inwhatdoestheprocessofdigestiondifferfromthoseprocesseswhicharecarriedoninthelaboratoryofthechemist？Evenifwetakethemostreconditeandmostcomplexoperationsofanimallife——thoseofthenervoussystem，theseoflateyearshavebeenshowntobe——Idonotsayidenticalinanysensewiththeelectricalprocesses——butthishasbeenshown，thattheyareinsomewayorotherassociatedwiththem。thatistosay，thateveryamountofnervousactionisaccompaniedbyacertainamountofelectricaldisturbanceintheparticlesofthenervesinwhichthatnervousactioniscarriedon。Inthiswaythenervousactionisrelatedtoelectricityinthesamewaythatheatisrelatedtoelectricity。andthesamesortofargumentwhichdemonstratesthetwolattertoberelatedtooneanothershowsthatthenervousforcesarecorrelatedtoelectricity。fortheexperimentsofM。DuboisReymondandothershaveshownthatwheneveranerveisinastateofexcitement，sendingamessagetothemusclesorconveyinganimpressiontothebrain，thereisadisturbanceoftheelectricalconditionofthatnervewhichdoesnotexistatothertimes。andthereareanumberofotherfactsandphenomenaofthatsort。sothatwecometothebroadconclusionthatnotonlyastolivingmatteritself，butastotheforcesthatmatterexerts，thereisacloserelationshipbetweentheorganicandtheinorganicworld——thedifferencebetweenthemarisingfromthediversecombinationanddispositionofidenticalforces，andnotfromanyprimarydiversity，sofaraswecansee。

IsaidjustnowthattheHorseeventuallydiedandbecameconvertedintothesameinorganicsubstancesfromwhenceallbutaninappreciablefractionofitssubstancedemonstrablyoriginated，sothattheactualwanderingsofmatterareasremarkableasthetransmigrationsofthesoulfabledbyIndiantradition。Butbeforedeathhasoccurred，intheonesexortheother，andinfactinboth，certainproductsorpartsoftheorganismhavebeensetfree，certainpartsoftheorganismsofthetwosexeshavecomeintocontactwithoneanother，andfromthatconjunction，fromthatunionwhichthentakesplace，thereresultstheformationofanewbeing。Atstatedtimesthemare，fromaparticularpartoftheinteriorofherbody，calledtheovary，getsridofaminuteparticleofmattercomparableinallessentialrespectswiththatwhichwecalledacellalittlewhilesince，whichcellcontainsakindofnucleusinitscentre，surroundedbyaclearspaceandbyaviscidmassofproteinsubstance(Fig。2)。andthoughitisdifferentinappearancefromtheeggswhichwearemostlyacquaintedwith，itisreallyanegg。Afteratimethisminuteparticleofmatter，whichmayonlybeasmallfractionofagraininweight，undergoesaseriesofchanges，——wonderful，complexchanges。Finally，uponitssurfacethereisfashionedalittleelevation，whichafterwardsbecomesdividedandmarkedbyagroove。Thelateralboundariesofthegrooveextendupwardsanddownwards，andatlengthgiverisetoadoubletube。Intheuppersmallertubethespinalmarrowandbrainarefashioned。inthelower，thealimentarycanalandheart。andatlengthtwopairsofbudsshootoutatthesidesofthebody，whicharetherudimentsofthelimbs。Infactatruedrawingofasectionoftheembryointhisstatewouldinallessentialrespectsresemblethatdiagramofahorsereducedtoitssimplestexpression，whichIfirstplacedbeforeyou(Fig。1)。

Slowlyandgraduallythesechangestakeplace。Thewholeofthebody，atfirst，canbebrokenupintocells，whichbecomeinoneplacemetamorphosedintomuscle，——inanotherplaceintogristleandbone，——inanotherplaceintofibroustissue，——andinanotherintohair。everypartbecominggraduallyandslowlyfashioned，asiftherewereanartificeratworkineachofthesecomplexstructuresthatwehavementioned。Thisembryo，asitiscalled，thenpassesintootherconditions。Ishouldtellyouthatthereisatimewhentheembryosofneitherdog，norhorse，norporpoise，normonkey，norman，canbedistinguishedbyanyessentialfeatureonefromtheother。thereisatimewhentheyeachandallofthemresemblethisoneoftheDog。Butasdevelopmentadvances，allthepartsacquiretheirspeciality，tillatlengthyouhavetheembryoconvertedintotheformoftheparentfromwhichitstarted。Sothatyousee，thislivinganimal，thishorse，beginsitsexistenceasaminuteparticleofnitrogenousmatter，which，beingsuppliedwithnutriment(derived，asIhaveshown，fromtheinorganicworld)，growsupaccordingtothespecialtypeandconstructionofitsparents，worksandundergoesaconstantwaste，andthatwasteismadegoodbynutrimentderivedfromtheinorganicworld。

thewastegivenoffinthiswaybeingdirectlyaddedtotheinorganicworld。andeventuallytheanimalitselfdies，and，bytheprocessofdecomposition，itswholebodyisreturnedtothoseconditionsofinorganicmatterinwhichitssubstanceoriginated。

This，then，isthatwhichistrueofeverylivingform，fromthelowestplanttothehighestanimal——tomanhimself。YoumightdefinethelifeofeveryoneinexactlythesametermsasthosewhichIhavenowused。

thedifferencebetweenthehighestandthelowestbeingsimplyinthecomplexityofthedevelopmentalchanges，thevarietyofthestructuralforms，thediversityofthephysiologicalfunctionswhichareexertedbyeach。

IfIweretotakeanoaktreeasaspecimenoftheplantworld，I

shouldfindthatitoriginatedinanacorn，which，too，commencedinacell。theacornisplacedintheground，anditveryspeedilybeginstoabsorbtheinorganicmattersIhavenamed，addsenormouslytoitsbulk，andwecanseeit，yearafteryear，extendingitselfupwardanddownward，attractingandappropriatingtoitselfinorganicmaterials，whichitvivifies，andeventually，asitripens，givesoffitsownproperacorns，whichagainrunthesamecourse。ButIneednotmultiplyexamples，——fromthehighesttothelowesttheessentialfeaturesoflifearethesame，asIhavedescribedineachofthesecases。

Somuch，then，fortheseparticularfeaturesoftheorganicworld，whichyoucanunderstandandcomprehend，solongasyouconfineyourselftoonesortoflivingbeing，andstudythatonly。

But，asyouknow，horsesarenottheonlylivingcreaturesintheworld。andagain，horses，likeallotheranimals，havecertainlimits——areconfinedtoacertainareaonthesurfaceoftheearthonwhichwelive，——and，asthatisthesimplermatter，Imaytakethatfirst。Initswildstate，andbeforethediscoveryofAmerica，whenthenaturalstateofthingswasinterferedwithbytheSpaniards，theHorsewasonlytobefoundinpartsoftheearthwhichareknowntogeographersastheOldWorld。thatistosay，youmightmeetwithhorsesinEurope，Asia，orAfrica。buttherewerenoneinAustralia，andtherewerenonewhatsoeverinthewholecontinentofAmerica，fromLabradordowntoCapeHorn。Thisisanempiricalfact，anditiswhatiscalled，statedinthewayIhavegivenityou，the’GeographicalDistribution’oftheHorse。

WhyhorsesshouldbefoundinEurope，Asia，andAfrica，andnotinAmerica，isnotobvious。theexplanationthattheconditionsoflifeinAmericaareunfavourabletotheirexistence，andthat，therefore，theyhadnotbeencreatedthere，evidentlydoesnotapply。forwhentheinvadingSpaniards，orourownyeomenfarmers，conveyedhorsestothesecountriesfortheirownuse，theywerefoundtothrivewellandmultiplyveryrapidly。andmanyareevennowrunningwildinthosecountries，andinaperfectlynaturalcondition。Now，supposeweweretodoforeveryanimalwhatwehaveheredonefortheHorse，——thatis，tomarkoffanddistinguishtheparticulardistrictorregiontowhicheachbelonged。andsupposingwetabulatedalltheseresults，thatwouldbecalledtheGeographicalDistributionofanimals，whileacorrespondingstudyofplantswouldyieldasaresulttheGeographicalDistributionofplants。

Ipassonfromthatnow，asImerelywishedtoexplaintoyouwhatI

meantbytheuseoftheterm’GeographicalDistribution。’AsIsaid，thereisanotheraspect，andamuchmoreimportantone，andthatis，therelationsofthevariousanimalstooneanother。TheHorseisaverywell-definedmatter-of-factsortofanimal，andweareallprettyfamiliarwithitsstructure。Idaresayitmayhavestruckyou，thatitresemblesverymuchnoothermemberoftheanimalkingdom，exceptperhapstheZebraortheAss。Butletmeaskyoutolookalongthesediagrams。HereistheskeletonoftheHorse，andheretheskeletonoftheDog。YouwillnoticethatwehaveintheHorseaskull，abackboneandribs，shoulder-bladesandhaunch-bones。Inthefore-limb，oneupperarm-bone，twoforearm-bones，wrist-bones(wronglycalledknee)，andmiddlehand-bones，endinginthethreebonesofafinger，thelastofwhichissheathedinthehornyhoofofthefore-foot：inthehind-limb，onethigh-bone，twoleg-bones，anklebones，andmiddlefoot-bones，endinginthethreebonesofatoe，thelastofwhichisencasedinthehoofofthehind-foot。NowturntotheDog’sskeleton。

Wefindidenticallythesamebones，butmoreofthem，therebeingmoretoesineachfoot，andhencemoretoe-bones。

Well，thatisaverycuriousthing！ThefactisthattheDogandtheHorse——whenonegetsalookatthemwithouttheoutwardimpedimentsoftheskin——arefoundtobemadeinverymuchthesamesortoffashion。

AndifIweretomakeatransversesectionoftheDog，IshouldfindthesameorgansthatIhavealreadyshownyouasformingpartsoftheHorse。Well，hereisanotherskeleton——thatofakindofLemur——youseehehasjustthesamebones。andifIweretomakeatransversesectionofit，itwouldbejustthesameagain。Inyourmind’seyeturnhimround，soastoputhisbackboneinapositioninclinedobliquelyupwardsandforwards，justasinthenextthreediagrams，whichrepresenttheskeletonsofanOrang，aChimpanzee，aGorilla，andyoufindyouhavenotroubleinidentifyingthebonesthroughout。andlastlyturntotheendoftheseries，thediagramrepresentingaman’sskeleton，andstillyoufindnogreatstructuralfeatureessentiallyaltered。Therearethesamebonesinthesamerelations。FromtheHorsewepassonandon，withgradualsteps，untilwearriveatlastatthehighestknownforms。Ontheotherhand，taketheotherlineofdiagrams，andpassfromtheHorsedownwardsinthescaletothisfish。

andstill，thoughthemodificationsarevastlygreater，theessentialframeworkoftheorganizationremainsunchanged。Here，forinstance，isaPorpoise：hereisitsstrongbackbone，withthecavityrunningthroughit，whichcontainsthespinalcord。herearetheribs，heretheshoulderblade。hereisthelittleshortupper-armbone，herearethetwoforearmbones，thewrist-bone，andthefinger-bones。

Strange，isitnot，thatthePorpoiseshouldhaveinthisqueer-

lookingaffair——itsflapper(asitiscalled)，thesamefundamentalelementsasthefore-legoftheHorseortheDog，ortheApeorMan。

andhereyouwillnoticeaverycuriousthing，——thehinderlimbsareabsent。Now，letusmakeanotherjump。LetusgototheCodfish：

hereyouseeistheforearm，inthislargepectoralfin——carryingyourmind’seyeonwardfromtheflapperofthePorpoise。Andhereyouhavethehinderlimbsrestoredintheshapeoftheseventralfins。IfI

weretomakeatransversesectionofthis，Ishouldfindjustthesameorgansthatwehavebeforenoticed。Sothat，yousee，therecomesoutthisstrangeconclusionastheresultofourinvestigations，thattheHorse，whenexaminedandcomparedwithotheranimals，isfoundbynomeanstostandaloneinnature。butthatthereareanenormousnumberofothercreatureswhichhavebackbones，ribs，andlegs，andotherpartsarrangedinthesamegeneralmanner，andinalltheirformationexhibitingthesamebroadpeculiarities。

Iamsurethatyoucannothavefollowedmeeveninthisextremelyelementaryexpositionofthestructuralrelationsofanimals，withoutseeingwhatIhavebeendrivingatallthrough，whichis，toshowyouthat，stepbystep，naturalistshavecometotheideaofaunityofplan，orconformityofconstruction，amonganimalswhichappearedatfirstsighttobeextremelydissimilar。

Andhereyouhaveevidenceofsuchaunityofplanamongalltheanimalswhichhavebackbones，andwhichwetechnicallycallVertebrata。Buttherearemultitudesofotheranimals，suchascrabs，lobsters，spiders，andsoon，whichwetermAnnulosa。IntheseIcouldnotpointouttoyouthepartsthatcorrespondwiththoseoftheHorse，——thebackbone，forinstance，——astheyareconstructeduponaverydifferentprinciple，whichisalsocommontoallofthem。

thatistosay，theLobster，theSpider，andtheCentipede，haveacommonplanrunningthroughtheirwholearrangement，injustthesamewaythattheHorse，theDog，andthePorpoiseassimilatetoeachother。

Yetothercreatures——whelks，cuttlefishes，oysters，snails，andalltheirtribe(Mollusca)——resembleoneanotherinthesameway，butdifferfrombothVertebrataandAnnulosa。andthelikeistrueoftheanimalscalledCoelenterata(Polypes)andProtozoa(animalculesandsponges)。

Now，bypursuingthissortofcomparison，naturalistshavearrivedattheconvictionthatthereare，——somethinkfive，andsomeseven，——butcertainlynotmorethanthelatternumber——andperhapsitissimplertoassumefive——distinctplansorconstructionsinthewholeoftheanimalworld。andthatthehundredsofthousandsofspeciesofcreaturesonthesurfaceoftheearth，areallreducibletothosefive，or，atmost，seven，plansoforganization。

Butcanwegonofurtherthanthat？Whenonehasgotsofar，oneistemptedtogoonastepandinquirewhetherwecannotgobackyetfurtherandbringdownthewholetomodificationsofoneprimordialunit。Theanatomistcannotdothis。butifhecalltohisaidthestudyofdevelopment，hecandoit。Forweshallfindthat，distinctasthoseplansare，whetheritbeaporpoiseorman，orlobster，oranyofthoseotherkindsIhavementioned，everyonebeginsitsexistencewithoneandthesameprimitiveform，——thatoftheegg，consisting，aswehaveseen，ofanitrogenoussubstance，havingasmallparticleornucleusinthecentreofit。Furthermore，theearlierchangesofeacharesubstantiallythesame。Anditisinthisthatliesthattrueunityoforganizationoftheanimalkingdomwhichhasbeenguessedatandfanciedformanyyears。butwhichithasbeenlefttothepresenttimetobedemonstratedbythecarefulstudyofdevelopment。Butisitpossibletogoanotherstepfurtherstill，andtoshowthatinthesamewaythewholeoftheorganicworldisreducibletooneprimitiveconditionofform？Isthereamongtheplantsthesameprimitiveformoforganization，andisthatidenticalwiththatoftheanimalkingdom？Thereplytothatquestion，too，isnotuncertainordoubtful。Itisnowprovedthateveryplantbeginsitsexistenceunderthesameform。thatistosay，inthatofacell——aparticleofnitrogenousmatterhavingsubstantiallythesameconditions。Sothatifyoutracebacktheoaktoitsfirstgerm，oraman，orahorse，orlobster，oroyster，oranyotheranimalyouchoosetoname，youshallfindeachandallofthesecommencingtheirexistenceinformsessentiallysimilartoeachother：and，furthermore，thatthefirstprocessesofgrowth，andmanyofthesubsequentmodifications，areessentiallythesameinprincipleinalmostall。

Inconclusion，letme，inafewwords，recapitulatethepositionswhichIhavelaiddown。AndyoumustunderstandthatIhavenotbeentalkingmeretheory。IhavebeenspeakingofmatterswhichareasplainlydemonstrableasthecommonestpropositionsofEuclid——offactsthatmustformthebasisofallspeculationsandbeliefsinBiologicalscience。Wehavegraduallytraceddownallorganicforms，or，inotherwords，wehaveanalyzedthepresentconditionofanimatednature，untilwefoundthateachspeciestookitsorigininaformsimilartothatunderwhichalltheotherscommencetheirexistence。Wehavefoundthewholeofthevastarrayoflivingforms，withwhichwearesurrounded，constantlygrowing，increasing，decayinganddisappearing。theanimalconstantlyattracting，modifying，andapplyingtoitssustenancethematterofthevegetablekingdom，whichderiveditssupportfromtheabsorptionandconversionofinorganicmatter。Andsoconstantanduniversalisthisabsorption，waste，andreproduction，thatitmaybesaidwithperfectcertaintythatthereisleftinnooneofourbodiesatthepresentmomentamillionthpartofthematterofwhichtheywereoriginallyformed！Wehaveseen，again，thatnotonlyisthelivingmatterderivedfromtheinorganicworld，butthattheforcesofthatmatterareallofthemcorrelativewithandconvertibleintothoseofinorganicnature。

This，forourpresentpurposes，isthebestviewofthepresentconditionoforganicnaturewhichIcanlaybeforeyou：itgivesyouthegreatoutlinesofavastpicture，whichyoumustfillupbyyourownstudy。

InthenextlectureIshallendeavourinthesamewaytogobackintothepast，andtosketchinthesamebroadmannerthehistoryoflifeinepochsprecedingourown。

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THEPASTCONDITIONOFORGANICNATURE

INthelecturewhichIdeliveredlastMondayevening，Iendeavouredtosketchinaverybriefmanner，butaswellasthetimeatmydisposalwouldpermit，thepresentconditionoforganicnature，meaningbythatlargetitlesimplyanindicationofthegreat，broad，andgeneralprincipleswhicharetobediscoveredbythosewholookattentivelyatthephenomenaoforganicnatureasatpresentdisplayed。Thegeneralresultofourinvestigationsmightbesummedupthus：wefoundthatthemultiplicityoftheformsofanimallife，greatasthatmaybe，maybereducedtoacomparativelyfewprimitiveplansortypesofconstruction。

thatafurtherstudyofthedevelopmentofthosedifferentformsrevealedtousthattheywereagainreducible，untilweatlastbroughttheinfinitediversityofanimal，andevenvegetablelife，downtotheprimordialformofasinglecell。

Wefoundthatouranalysisoftheorganicworld，whetheranimalsorplants，showed，inthelongrun，thattheymightbothbereducedinto，andwere，infact，composedof，thesameconstituents。Andwesawthattheplantobtainedthematerialsconstitutingitssubstancebyapeculiarcombinationofmattersbelongingentirelytotheinorganicworld。that，then，theanimalwasconstantlyappropriatingthenitrogenousmattersoftheplanttoitsownnourishment，andreturningthembacktotheinorganicworld，inwhatwespokeofasitswaste。andthatfinally，whentheanimalceasedtoexist，theconstituentsofitsbodyweredissolvedandtransmittedtothatinorganicworldwhencetheyhadbeenatfirstabstracted。Thuswesawinboththebladeofgrassandthehorsebutthesameelementsdifferentlycombinedandarranged。

Wediscoveredacontinualcirculationgoingon，——theplantdrawingintheelementsofinorganicnatureandcombiningthemintofoodfortheanimalcreation。theanimalborrowingfromtheplantthematterforitsownsupport，givingoffduringitslifeproductswhichreturnedimmediatelytotheinorganicworld。andthat，eventually，theconstituentmaterialsofthewholestructureofbothanimalsandplantswerethusreturnedtotheiroriginalsource：therewasaconstantpassagefromonestateofexistencetoanother，andareturningbackagain。

Lastly，whenweendeavouredtoformsomenotionofthenatureoftheforcesexercisedbylivingbeings，wediscoveredthatthey——ifnotcapableofbeingsubjectedtothesameminuteanalysisastheconstituentsofthosebeingsthemselves——thattheywerecorrelativewith——thattheyweretheequivalentsoftheforcesofinorganicnature——thattheywere，inthesenseinwhichthetermisnowused，convertiblewiththem。Thatwasourgeneralresult。

Andnow，leavingthePresent，ImustendeavourinthesamemannertoputbeforeyouthefactsthataretobediscoveredinthePasthistoryofthelivingworld，inthepastconditionsoforganicnature。Wehave，to-night，todealwiththefactsofthathistory——ahistoryinvolvingperiodsoftimebeforewhichourmerehumanrecordssinkintoutterinsignificance——ahistorythevarietyandphysicalmagnitudeofwhoseeventscannotevenbeforeshadowedbythehistoryofhumanlifeandhumanphenomena——ahistoryofthemostvariedandcomplexcharacter。

Wemustdealwiththehistory，then，inthefirstplace，asweshoulddealwithallotherhistories。Thehistoricalstudentknowsthathisfirstbusinessshouldbetoinquireintothevalidityofhisevidence，andthenatureoftherecordinwhichtheevidenceiscontained，thathemaybeabletoformaproperestimateofthecorrectnessoftheconclusionswhichhavebeendrawnfromthatevidence。So，here，wemustpass，inthefirstplace，totheconsiderationofamatterwhichmayseemforeigntothequestionunderdiscussion。Wemustdwelluponthenatureoftherecords，andthecredibilityoftheevidencetheycontain。wemustlooktothecompletenessorincompletenessofthoserecordsthemselves，beforeweturntothatwhichtheycontainandreveal。Thequestionofthecredibilityofthehistory，happilyforus，willnotrequiremuchconsideration，for，inthishistory，unlikethoseofhumanorigin，therecanbenocavilling，nodifferencesastotherealityandtruthofthefactsofwhichitismadeup。thefactsstatethemselves，andarelaidoutclearlybeforeus。

But，althoughoneofthegreatestdifficultiesofthehistoricalstudentisclearedoutofourpath，thereareotherdifficulties——difficultiesinrightlyinterpretingthefactsastheyarepresentedtous——whichmaybecomparedwiththegreatestdifficultiesofanyotherkindsofhistoricalstudy。

Whatisthisrecordofthepasthistoryoftheglobe，andwhatarethequestionswhichareinvolvedinaninquiryintoitscompletenessorincompleteness？Thatrecordiscomposedofmud。andthequestionwhichwehavetoinvestigatethiseveningresolvesitselfintoaquestionoftheformationofmud。Youmaythink，perhaps，thatthisisavaststep——ofalmostfromthesublimetotheridiculous——fromthecontemplationofthehistoryofthepastagesoftheworld’sexistencetotheconsiderationofthehistoryoftheformationofmud！But，innature，thereisnothingmeanandunworthyofattention。thereisnothingridiculousorcontemptibleinanyofherworks。andthisinquiry，youwillsoonsee，Ihope，takesustotheveryrootandfoundationsofoursubject。

How，then，ismudformed？Always，withsometriflingexception，whichI

neednotconsidernow——always，astheresultoftheactionofwater，wearingdownanddisintegratingthesurfaceoftheearthandrockswithwhichitcomesincontact——poundingandgrindingitdown，andcarryingtheparticlesawaytoplaceswheretheyceasetobedisturbedbythismechanicalaction，andwheretheycansubsideandrest。Fortheocean，urgedbywinds，washes，asweknow，alongextentofcoast，andeverywave，loadedasitiswithparticlesofsandandgravelasitbreaksupontheshore，doessomethingtowardsthedisintegratingprocess。Andthus，slowlybutsurely，thehardestrocksaregraduallygrounddowntoapowderysubstance。andthemudthusformed，coarserorfiner，asthecasemaybe，iscarriedbytherushofthetides，orcurrents，tillitreachesthecomparativelydeeperpartsoftheocean，inwhichitcansinktothebottom，thatis，topartswherethereisadepthofaboutfourteenorfifteenfathoms，adepthatwhichthewateris，usually，nearlymotionless，andinwhich，ofcourse，thefinerparticlesofthisdetritus，ormudaswecallit，sinkstothebottom。

Or，again，ifyoutakeariver，rushingdownfromitsmountainsources，brawlingoverthestonesandrocksthatintersectitspath，loosening，removing，andcarryingwithitinitsdownwardcoursethepebblesandlightermattersfromitsbanks，itcrushesandpoundsdowntherocksandearthsinpreciselythesamewayasthewearingactionoftheseawaves。Themattersformingthedepositaretornfromthemountain-sideandwhirledimpetuouslyintothevalley，moreslowlyovertheplain，thenceintotheestuary，andfromtheestuarytheyaresweptintothesea。Thecoarserandheavierfragmentsareobviouslydepositedfirst，thatis，assoonasthecurrentbeginstoloseitsforcebybecomingamalgamatedwiththestillerdepthsoftheocean，butthefinerandlighterparticlesarecarriedfurtheron，andeventuallydepositedinadeeperandstillerportionoftheocean。

Itclearlyfollowsfromthisthatmudgivesusachronology。foritisevidentthatsupposingthis，whichInowsketch，tobetheseabottom，andsupposingthistobeacoast-line。fromthewashingactionoftheseaupontherock，wearingandgrindingitdownintoasedimentofmud，themudwillbecarrieddown，andatlength，depositedinthedeeperpartsofthisseabottom，whereitwillformalayer。andthen，whilethatfirstlayerishardening，othermudwhichiscomingfromthesamesourcewill，ofcourse，becarriedtothesameplace。and，asitisquiteimpossibleforittogetbeneaththelayeralreadythere，itdepositsitselfaboveit，andformsanotherlayer，andinthatwayyougraduallyhavelayersofmudconstantlyformingandhardeningoneabovetheother，andconveyingarecordoftime。

Itisanecessaryresultoftheoperationofthelawofgravitationthattheuppermostlayershallbetheyoungestandthelowesttheoldest，andthatthedifferentbedsshallbeolderatanyparticularpointorspotinexactlytheratiooftheirdepthfromthesurface。Sothatiftheywereupheavedafterwards，andyouhadaseriesofthesedifferentlayersofmud，convertedintosandstone，orlimestone，asthecasemightbe，youmightbesurethatthebottomlayerwasdepositedfirst，andthattheupperlayerswereformedafterwards。Here，yousee，isthefirststepinthehistory——theselayersofmudgiveusanideaoftime。

Thewholesurfaceoftheearth，——Ispeakbroadly，andleaveoutminorqualifications，——ismadeupofsuchlayersofmud，sohard，themajorityofthem，thatwecallthemrockwhetherlimestoneorsandstone，orothervarietiesofrock。And，seeingthateverypartofthecrustoftheearthismadeupinthisway，youmightthinkthatthedeterminationofthechronology，thefixingofthetimewhichithastakentoformthiscrustisacomparativelysimplematter。Takeabroadaverage，ascertainhowfastthemudisdepositeduponthebottomofthesea，orintheestuaryofrivers。takeittobeaninch，ortwo，orthreeinchesayear，orwhateveryoumayroughlyestimateitat。

thentakethetotalthicknessofthewholeseriesofstratifiedrocks，whichgeologistsestimateattwelveorthirteenmiles，oraboutseventythousandfeet，makeasuminshortdivision，dividethetotalthicknessbythatofthequantitydepositedinoneyear，andtheresultwill，ofcourse，giveyouthenumberofyearswhichthecrusthastakentoform。

Truly，thatlooksaverysimpleprocess！Itwouldbesoexceptforcertaindifficulties，theveryfirstofwhichisthatoffindinghowrapidlysedimentsaredeposited。butthemaindifficulty——adifficultywhichrendersanycertaincalculationsofsuchamatteroutofthequestion——isthis，thesea-bottomonwhichthedeposittakesplaceiscontinuallyshifting。

Insteadofthesurfaceoftheearthbeingthatstable，fixedthingthatitispopularlybelievedtobe，being，incommonparlance，theveryemblemoffixityitself，itisincessantlymoving，andis，infact，asunstableasthesurfaceofthesea，exceptthatitsundulationsareinfinitelyslowerandenormouslyhigheranddeeper。

Now，whatistheeffectofthisoscillation？TakethecasetowhichI

havepreviouslyreferred。Thefinerorcoarsersedimentsthatarecarrieddownbythecurrentoftheriver，willonlybecarriedoutacertaindistance，andeventually，aswehavealreadyseen，onreachingthestillerpartoftheocean，willbedepositedatthebottom。

LetCy(Fig。4)bethesea-bottom，yDtheshore，xythesea-level，thenthecoarserdepositwillsubsideovertheregionB，thefineroverA，whilebeyondAtherewillbenodepositatall。and，consequently，norecordwillbekept，simplybecausenodepositisgoingon。Now，supposethatthewholeland，C，D，whichwehaveregardedasstationary，goesdown，asitdoesso，bothAandBgofurtheroutfromtheshore，whichwillbeatyl。x1，y1，beingthenewsea-level。Theconsequencewillbethatthelayerofmud(A)，beingnow，forthemostpart，furtherthantheforceofthecurrentisstrongenoughtoconveyeventhefinest’debris’，will，ofcourse，receivenomoredeposits，andhavingattainedacertainthicknesswillnowgrownothicker。

Weshouldbemisledintakingthethicknessofthatlayer，wheneveritmaybeexposedtoourview，asarecordoftimeinthemannerinwhichwearenowregardingthissubject，asitwouldgiveusonlyanimperfectandpartialrecord：itwouldseemtorepresenttooshortaperiodoftime。

Fig。4。

Suppose，ontheotherhand，thattheland(CD)hadgoneonrisingslowlyandgradually——sayaninchortwoinchesinthecourseofacentury，——whatwouldbethepracticaleffectofthatmovement？Why，thatthesedimentAandBwhichhasbeenalreadydeposited，wouldeventuallybebroughtnearertotheshore-level，andagainsubjectedtothewearandtearofthesea。anddirectlytheseabeginstoactuponit，itwouldofcoursesooncutupandcarryitaway，toagreaterorlessextent，tobere-depositedfurtherout。

Well，asthereis，inallprobability，notonesinglespotonthewholesurfaceoftheearth，whichhasnotbeenupanddowninthiswayagreatmanytimes，itfollowsthatthethicknessofthedepositsformedatanyparticularspotcannotbetaken(evensupposingwehadatfirstobtainedcorrectdataastotherateatwhichtheytookplace)asaffordingreliableinformationastotheperiodoftimeoccupiedinitsdeposit。Sothatyouseeitisabsolutelynecessaryfromthesefacts，seeingthatourrecordentirelyconsistsofaccumulationsofmud，superimposedoneontheother。seeinginthenextplacethatanyparticularspotsonwhichaccumulationshaveoccurred，havebeenconstantlymovingupanddown，andsometimesoutofthereachofadeposit，andatothertimesitsowndepositbrokenupandcarriedaway，itfollowsthatourrecordmustbeinthehighestdegreeimperfect，andwehavehardlyatraceleftofthickdeposits，oranydefiniteknowledgeoftheareathattheyoccupied，inagreatmanycases。Andmarkthis！Thatsupposingeventhatthewholesurfaceoftheearthhadbeenaccessibletothegeologist，——thatmanhadhadaccesstoeverypartoftheearth，andhadmadesectionsofthewhole，andputthemalltogether，——eventhenhisrecordmustofnecessitybeimperfect。

Buttohowmuchhasmanreallyaccess？IfyouwilllookatthisMapyouwillseethatitrepresentstheproportionoftheseatotheearth：

thiscolouredpartindicatesallthedryland，andthisotherportionisthewater。Youwillnoticeatoncethatthewatercoversthree-fifthsofthewholesurfaceoftheglobe，andhascovereditinthesamemannereversincemanhaskeptanyrecordofhisownobservations，tosaynothingoftheminuteperiodduringwhichhehascultivatedgeologicalinquiry。Sothatthree-fifthsofthesurfaceoftheearthisshutoutfromusbecauseitisunderthesea。Letuslookattheothertwo-fifths，andseewhatarethecountriesinwhichanythingthatmaybetermedsearchinggeologicalinquiryhasbeencarriedout：agooddealofFrance，Germany，andGreatBritainandIreland，bitsofSpain，ofItaly，andofRussia，havebeenexamined，butofthewholegreatmassofAfrica，exceptpartsofthesouthernextremity，weknownexttonothing。littlebitsofIndia，butofthegreaterpartoftheAsiaticcontinentnothing。bitsoftheNorthernAmericanStatesandofCanada，butofthegreaterpartofthecontinentofNorthAmerica，andinstilllargerproportion，ofSouthAmerica，nothing！

Underthesecircumstances，itfollowsthatevenwithreferencetothatkindofimperfectinformationwhichwecanpossess，itisonlyofabouttheten-thousandthpartoftheaccessiblepartsoftheearththathasbeenexaminedproperly。Therefore，itiswithjusticethatthemostthoughtfulofthosewhoareconcernedintheseinquiriesinsistcontinuallyupontheimperfectionofthegeologicalrecord。for，I

repeat，itisabsolutelynecessary，fromthenatureofthings，thatthatrecordshouldbeofthemostfragmentaryandimperfectcharacter。

Unfortunatelythiscircumstancehasbeenconstantlyforgotten。Menofscience，likeyoungcoltsinafreshpasture，areapttobeexhilaratedonbeingturnedintoanewfieldofinquiry，togooffatahand-gallop，intotaldisregardofhedgesandditches，losingsightofthereallimitationoftheirinquiries，andtoforgettheextremeimperfectionofwhatisreallyknown。Geologistshaveimaginedthattheycouldtelluswhatwasgoingonatallpartsoftheearth’ssurfaceduringagivenepoch。theyhavetalkedofthisdepositbeingcontemporaneouswiththatdeposit，until，fromourlittlelocalhistoriesofthechangesatlimitedspotsoftheearth’ssurface，theyhaveconstructedauniversalhistoryoftheglobeasfullofwondersandportentsasanyotherstoryofantiquity。

Butwhatdoesthisattempttoconstructauniversalhistoryoftheglobeimply？Itimpliesthatweshallnotonlyhaveapreciseknowledgeoftheeventswhichhaveoccurredatanyparticularpoint，butthatweshallbeabletosaywhatevents，atanyonespot，tookplaceatthesametimewiththoseatotherspots。

Letusseehowfarthatisinthenatureofthingspracticable。SupposethathereImakeasectionoftheLakeofKillarney，andherethesectionofanotherlake——thatofLochLomondinScotlandforinstance。

Theriversthatflowintothemareconstantlycarryingdowndepositsofmud，andbeds，orstrata，arebeingasconstantlyformed，oneabovetheother，atthebottomofthoselakes。Now，thereisnotashadowofdoubtthatinthesetwolakesthelowerbedsareallolderthantheupper——thereisnodoubtaboutthat。butwhatdoes’this’tellusabouttheageofanygivenbedinLochLomond，ascomparedwiththatofanygivenbedintheLakeofKillarney？Itis，indeed，obviousthatifanytwosetsofdepositsareseparatedanddiscontinuous，thereisabsolutelynomeanswhatevergivenyoubythenatureofthedepositofsayingwhetheroneismuchyoungerorolderthantheother。butyoumaysay，asmanyhavesaidandthink，thatthecaseisverymuchalteredifthebedswhichwearecomparingarecontinuous。Supposetwobedsofmudhardenedintorock，——AandB-areseeninsection。(Fig。5。)

[Fig。5。]

Well，yousay，itisadmittedthatthelowermostbedisalwaystheolder。Verywell。B，therefore，isolderthanA。Nodoubt，’asawhole’，itisso。orifanypartsofthetwobedswhichareinthesameverticallinearecompared，itisso。Butsupposeyoutakewhatseemsaverynaturalstepfurther，andsaythatthepart’a’ofthebedAisyoungerthanthepart’b’ofthebedB。Isthissoundreasoning？Ifyoufindanyrecordofchangestakingplaceat’b’，didtheyoccurbeforeanyeventswhichtookplacewhile’a’wasbeingdeposited？Itlooksallveryplainsailing，indeed，tosaythattheydid。andyetthereisnoproofofanythingofthekind。AstheformerDirectorofthisInstitution，SirH。DelaBeche，longagoshowed，thisreasoningmayinvolveanentirefallacy。Itisextremelypossiblethat’a’mayhavebeendepositedagesbefore’b’。Itisveryeasytounderstandhowthatcanbe。ToreturntoFig。4。whenAandBweredeposited，theywere’substantially’contemporaneous。Abeingsimplythefinerdeposit，andBthecoarserofthesamedetritusorwasteofland。Nowsupposethatthatsea-bottomgoesdown(asshowninFig。4)，sothatthefirstdepositiscarriednofartherthan’a’，formingthebedAl，andthecoarsenofartherthan’b’，formingthebedB1，theresultwillbetheformationoftwocontinuousbeds，oneoffinesediment(AA1)

over-lappinganotherofcoarsesediment(BBl)。Nowsupposethewholesea-bottomisraisedup，andasectionexposedaboutthepointAl。nodoubt，’atthisspot’，theupperbedisyoungerthanthelower。ButweshouldobviouslygreatlyerrifweconcludedthatthemassoftheupperbedatAwasyoungerthanthelowerbedatB。forwehavejustseenthattheyarecontemporaneousdeposits。StillmoreshouldwebeinerrorifwesupposedtheupperbedatAtobeyoungerthanthecontinuationofthelowerbedatBl。forAwasdepositedlongbeforeB1。Infine，if，insteadofcomparingimmediatelyadjacentpartsoftwobeds，oneofwhichliesuponanother，wecomparedistantparts，itisquitepossiblethattheuppermaybeanynumberofyearsolderthantheunder，andtheunderanynumberofyearsyoungerthantheupper。

NowyoumustnotsupposethatIputthisbeforeyouforthepurposeofraisingaparadoxicaldifficulty。thefactis，thatthegreatmassofdepositshavetakenplaceinsea-bottomswhicharegraduallysinking，andhavebeenformedundertheveryconditionsIamheresupposing。

DonotrunawaywiththenotionthatthissubvertstheprincipleIlaiddownatfirst。Theerrorliesinextendingaprinciplewhichisperfectlyapplicabletodepositsinthesameverticallinetodepositswhicharenotinthatrelationtooneanother。

Itisinconsequenceofcircumstancesofthiskind，andofothersthatI

mightmentiontoyou，thatourconclusionsonandinterpretationsoftherecordarereallyandstrictlyonlyvalidsolongasweconfineourselvestooneverticalsection。Idonotmeantotellyouthattherearenoqualifyingcircumstances，sothat，eveninveryconsiderableareas，wemaysafelyspeakofconformablysuperimposedbedsbeingolderoryoungerthanothersatmanydifferentpoints。Butwecanneverbequitesureincomingtothatconclusion，andespeciallywecannothesureifthereisanybreakintheircontinuity，oranyverygreatdistancebetweenthepointstobecompared。

Wellnow，somuchfortherecorditself，——somuchforitsimperfections，——somuchfortheconditionstobeobservedininterpretingit，anditschronologicalindications，themomentwepassbeyondthelimitsofaverticallinearsection。

Nowletuspassfromtherecordtothatwhichitcontains，——fromthebookitselftothewritingandthefiguresonitspages。Thiswritingandthesefiguresconsistofremainsofanimalsandplantswhich，inthegreatmajorityofcases，havelivedanddiedintheveryspotinwhichwenowfindthem，oratleastintheimmediatevicinity。Youmustallofyoubeaware——andIreferredtothefactinmylastlecture——thattherearevastnumbersofcreatureslivingatthebottomofthesea。Thesecreatures，likeallothers，soonerorlaterdie，andtheirshellsandhardpartslieatthebottom。andthenthefinemudwhichisbeingconstantlybroughtdownbyriversandtheactionofthewearandtearofthesea，coversthemoverandprotectsthemfromanyfurtherchangeoralteration。and，ofcourse，asinprocessoftimethemudbecomeshardenedandsolidified，theshellsoftheseanimalsarepreservedandfirmlyimbeddedinthelimestoneorsandstonewhichisbeingthusformed。YoumayseeinthegalleriesoftheMuseumupstairsspecimensoflimestonesinwhichsuchfossilremainsofexistinganimalsareimbedded。Therearesomespecimensinwhichturtles’eggshavebeenimbeddedincalcareoussand，andbeforethesunhadhatchedtheyoungturtles，theybecamecoveredoverwithcalcareousmud，andthushavebeenpreservedandfossilized。

Notonlydoesthisprocessofimbeddingandfossilizationoccurwithmarineandotheraquaticanimalsandplants，butitaffectsthoselandanimalsandplantswhicharedriftedawaytosea，orbecomeburiedinbogsormorasses。andtheanimalswhichhavebeentroddendownbytheirfellowsandcrushedinthemudattheriver’sbank，astheherdhavecometodrink。Inanyofthesecases，theorganismsmaybecrushedorbemutilated，beforeorafterputrefaction，insuchamannerthatperhapsonlyapartwillbeleftintheforminwhichitreachesus。Itis，indeed，amostremarkablefact，thatitisquiteanexceptionalcasetofindaskeletonofanyoneofallthethousandsofwildlandanimalsthatweknowareconstantlybeingkilled，ordyinginthecourseofnature：theyarepreyedonanddevouredbyotheranimalsordieinplaceswheretheirbodiesarenotafterwardsprotectedbymud。

Thereareotheranimalsexistinginthesea，theshellsofwhichformexceedinglylargedeposits。YouareprobablyawarethatbeforetheattemptwasmadetolaytheAtlantictelegraphiccable，theGovernmentemployedvesselsinmakingaseriesofverycarefulobservationsandsoundingsofthebottomoftheAtlantic。andalthough，aswemustallregret，uptothepresenttimethatprojecthasnotsucceeded，wehavethesatisfactionofknowingthatityieldedsomemostremarkableresultstoscience。TheAtlanticOceanhadtobesoundedrightacross，todepthsofseveralmilesinsomeplaces，andthenatureofitsbottomwascarefullyascertained。Well，now，aspaceofabout1，000mileswidefromeasttowest，andIdonotexactlyknowhowmanyfromnorthtosouth，butatanyrate600or700miles，wascarefullyexamined，anditwasfoundthatoverthewholeofthatimmenseareaanexcessivelyfinechalkymudisbeingdeposited。andthisdepositisentirelymadeupofanimalswhosehardpartsaredepositedinthispartoftheocean，andaredoubtlessgraduallyacquiringsolidityandbecomingmetamorphosedintoachalkylimestone。Thus，yousee，itisquitepossibleinthiswaytopreserveunmistakablerecordsofanimalandvegetablelife。

Wheneverthesea-bottom，bysomeofthoseundulationsoftheearth’scrustthatIhavereferredto，becomesupheaved，andsectionsorboringsaremade，orpitsaredug，thenwebecomeabletoexaminethecontentsandconstituentsoftheseancientsea-bottoms，andfindoutwhatmannerofanimalslivedatthatperiod。

Nowitisaveryimportantconsiderationinitsbearingonthecompletenessoftherecord，toinquirehowfartheremainscontainedinthesefossiliferouslimestonesareabletoconveyanythinglikeanaccurateorcompleteaccountoftheanimalswhichwereinexistenceatthetimeofitsformation。Uponthatpointwecanformaveryclearjudgment，andoneinwhichthereisnopossibleroomforanymistake。

Thereareofcourseagreatnumberofanimals——suchasjelly-fishes，andotheranimals——withoutanyhardparts，ofwhichwecannotreasonablyexpecttofindanytraceswhatever：thereisnothingofthemtopreserve。Withinaveryshorttime，youwillhavenoticed，aftertheyareremovedfromthewater，theydryuptoamerenothing。

certainlytheyarenotofanaturetoleaveanyveryvisibletracesoftheirexistenceonsuchbodiesaschalkormud。Thenagain，lookatlandanimals。itis，asIhavesaid，averyuncommonthingtofindalandanimalentireafterdeath。Insectsandothercarnivorousanimalsveryspeedilypullthemtopieces，putrefactiontakesplace，andso，outofthehundredsofthousandsthatareknowntodieeveryyear，itistherarestthingintheworldtoseeoneimbeddedinsuchawaythatitsremainswouldbepreservedforalengthenedperiod。Notonlyisthisthecase，butevenwhenanimalremainshavebeensafelyimbedded，certainnaturalagentsmaywhollydestroyandremovethem。

Almostallthehardpartsofanimals——thebonesandsoon——arecomposedchieflyofphosphateoflimeandcarbonateoflime。Someyearsago，I

hadtomakeaninquiryintothenatureofsomeverycuriousfossilssenttomefromtheNorthofScotland。FossilsareusuallyhardbonystructuresthathavebecomeimbeddedinthewayIhavedescribed，andhavegraduallyacquiredthenatureandsolidityofthebodywithwhichtheyareassociated。butinthiscaseIhadaseriesof’holes’insomepiecesofrock，andnothingelse。Thoseholes，however，hadacertaindefiniteshapeaboutthem，andwhenIgotaskilfulworkmantomakecastingsoftheinterioroftheseholes，Ifoundthattheyweretheimpressionsofthejointsofabackboneandofthearmourofagreatreptile，twelveormorefeetlong。Thisgreatbeasthaddiedandgotburiedinthesand。thesandhadgraduallyhardenedoverthebones，butremainedporous。Waterhadtrickledthroughit，andthatwaterbeingprobablychargedwithasuperfluityofcarbonicacid，haddissolvedallthephosphateandcarbonateoflime，andthebonesthemselveshadthusdecayedandentirelydisappeared。butasthesandstonehappenedtohaveconsolidatedbythattime，thepreciseshapeoftheboneswasretained。

Ifthatsandstonehadremainedsoftalittlelonger，weshouldhaveknownnothingwhatsoeveroftheexistenceofthereptilewhosebonesithadencased。

Howcertainitisthatavastnumberofanimalswhichhaveexistedatoneperiodonthisearthhaveentirelyperished，andleftnotracewhateveroftheirforms，maybeprovedtoyoubyotherconsiderations。

Therearelargetractsofsandstoneinvariouspartsoftheworld，inwhichnobodyhasyetfoundanythingbutfootsteps。Notaboneofanydescription，butanenormousnumberoftracesoffootsteps。Thereisnoquestionaboutthem。ThereisawholevalleyinConnecticutcoveredwiththesefootsteps，andnotasinglefragmentoftheanimalswhichmadethemhasyetbeenfound。Letmementionanothercasewhileuponthatmatter，whichisevenmoresurprisingthanthosetowhichIhaveyetreferred。ThereisalimestoneformationnearOxford，ataplacecalledStonesfield，whichhasyieldedtheremainsofcertainveryinterestingmammaliananimals，anduptothistime，ifIrecollectrightly，therehavebeenfoundsevenspecimensofitslowerjaws，andnotabitofanythingelse，neitherlimb-bonesnorskull，oranypartwhatever。notafragmentofthewholesystem！Ofcourse，itwouldbepreposteroustoimaginethatthebeastshadnothingelsebutalowerjaw！Theprobabilityis，asDr。Bucklandshowed，astheresultofhisobservationsondeaddogsintheriverThames，thatthelowerjaw，notbeingsecuredbyveryfirmligamentstothebonesofthehead，andbeingaweightyaffair，wouldeasilybeknockedoff，ormightdropawayfromthebodyasitfloatedinwaterinastateofdecomposition。Thejawwouldthusbedepositedimmediately，whiletherestofthebodywouldfloatanddriftawayaltogether，ultimatelyreachingthesea，andperhapsbecomingdestroyed。Thejawbecomescoveredupandpreservedintheriversilt，andthusitcomesthatwehavesuchacuriouscircumstanceasthatofthelowerjawsintheStonesfieldslates。Sothat，yousee，faultyastheselayersofstoneintheearth’scrustare，defectiveastheynecessarilyareasarecord，theaccountofcontemporaneousvitalphenomenapresentedbythemis，bythenecessityofthecase，infinitelymoredefectiveandfragmentary。

ItwasnecessarythatIshouldputallthisverystronglybeforeyou，because，otherwise，youmighthavebeenledtothinkdifferentlyofthecompletenessofourknowledgebythenextfactsIshallstatetoyou。

Theresearchesofthelastthree-quartersofacenturyhave，intruth，revealedawonderfulrichnessoforganiclifeinthoserocks。Certainlynotfewerthanthirtyorfortythousanddifferentspeciesoffossilshavebeendiscovered。Youhavenomoregroundfordoubtingthatthesecreaturesreallylivedanddiedatorneartheplacesinwhichwefindthemthanyouhaveforlikescepticismaboutashellonthesea-shore。

Theevidenceisasgoodintheonecaseasintheother。

Ournextbusinessistolookatthegeneralcharacterofthesefossilremains，anditisasubjectwhichitwillberequisitetoconsidercarefully。andthefirstpointforusistoexaminehowmuchtheextinct’Flora’and’Fauna’asa’whole’——disregardingaltogetherthe’succession’oftheirconstituents，ofwhichIshallspeakafterwards——differfromthe’Flora’and’Fauna’ofthepresentday——howfartheydifferinwhatwe’do’knowaboutthem，leavingaltogetheroutofconsiderationspeculationsbaseduponwhatwe’donot’know。

Istronglyimaginethatifitwerenotforthepeculiarappearancethatfossilisedanimalshave，anyofyoumightreadilywalkthroughamuseumwhichcontainsfossilremainsmixedupwiththoseofthepresentformsoflife，andIdoubtverymuchwhetheryouruninstructedeyeswouldleadyoutoseeanyvastorwonderfuldifferencebetweenthetwo。Ifyoulookedclosely，youwouldnotice，inthefirstplace，agreatmanythingsverylikeanimalswithwhichyouareacquaintednow：youwouldseedifferencesofshapeandproportion，butonthewholeaclosesimilarity。

IexplainedwhatImeantbyORDERStheotherday，whenIdescribedtheanimalkingdomasbeingdividedinsub-kingdoms，classesandorders。Ifyoudividetheanimalkingdomintoorders，youwillfindthatthereareaboutonehundredandtwenty。Thenumbermayvaryononesideortheother，butthisisafairestimate。Thatisthesumtotaloftheordersofalltheanimalswhichweknownow，andwhichhavebeenknowninpasttimes，andleftremainsbehind。

Now，howmanyofthoseareabsolutelyextinct？Thatistosay，howmanyoftheseordersofanimalshavelivedataformerperiodoftheworld’shistory，buthaveatpresentnorepresentatives？ThatisthesenseinwhichImeanttousethewordextinct。Imeanthatthoseanimalsdidliveonthisearthatonetime，buthaveleftnooneoftheirkindwithusatthepresentmoment。Sothatestimatingthenumberofextinctanimalsisasortofwayofcomparingthepastcreationasawholewiththepresentasawhole。Amongthemammaliaandbirdstherearenoneextinct。butwhenwecometothereptilesthereisamostwonderfulthing：outoftheeightorders，orthereabouts，whichyoucanmakeamongreptiles，one-halfareextinct。Thesediagramsoftheplesiosaurus，theichthyosaurus，thepterodactyle，giveyouanotionofsomeoftheseextinctreptiles。Andhereisacastofthepterodactyleandbonesoftheichthyosaurusandtheplesiosaurus，justasfreshasifithadbeenrecentlydugupinachurchyard。Thus，inthereptileclass，therearenolessthanhalfoftheorderswhichareabsolutelyextinct。Ifweturntothe’Amphibia’，therewasoneextinctorder，theLabyrinthodonts，typifiedbythelargesalamander-likebeastshowninthisdiagram。

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