Eachorganasitisdeveloped，serves，byitsactionsandreactionsonthe
　　rest，toinitiatenewcomplexities。Thefirstpulsationsofthefoetalheart
　　mustsimultaneouslyaidtheunfoldingofeverypart。Thegrowthofeachtissue，
　　bytakingfromthebloodspecialproportionsofelements，mustmodifythe
　　constitutionoftheblood;andsomustmodifythenutritionofalltheother
　　tissues。Thedistributiveactions，implyingastheydoacertainwaste，necessitate
　　anadditiontothebloodofeffetematters，whichmustinfluencetherest
　　ofthesystem，andperhaps，assomethink，initiatetheformationofexcretory
　　organs。Thenervousconnexionsestablishedamongthevisceramustfurther
　　multiplytheirmutualinfluences。Andsoisitwitheverymodificationof
　　structure——everyadditionalpartandeveryalterationintheratiosof
　　parts。Proofofamoredirectkindisfurnishedbythefact，thatthesame
　　germmaybeevolvedintodifferentformsaccordingtocircumstances。Thus，
　　duringitsearlieststages，everygermissexless——originateseithermale
　　orfemaleasthebalanceofforcesactingonitdetermines。Again，there
　　isthefamiliartruththatthelarvaofaworking—beewilldevelopintoa
　　queen—beeif，beforeacertainperiod，itisfedafteramannerlikethat
　　inwhichthelarvaeofqueen—beesarefed。Thenthereisthestillmorestriking
　　evidencefurnishedbyantsandtermites。Riley，Grassi，Haviland，andHart，
　　haveshownthatdifferencesofnutritionnotonlyoriginatethedifferences
　　betweenmalesandfemalesbutalsothedifferenttraitsofsolders，workers，
　　andnurses。*Varying
　　degreeofnutrition，afterinitiatingtheunlikenessofsex，thendetermines
　　theunlikenessesofexternalorganspossessedbythevariousclassesofsexless
　　individuals。Nextcomestheevidence，stillmoredirectlyrelevant，supplied
　　bytheeffectsofcastration。Iftheremovalofcertainorganspreventsthe
　　developmentofcertainotherorgansinremotepartsofthesystem——inman
　　thevocalstructures，thebeard，sometraitsofgeneralform，someinstincts
　　andothermentalcharacters——thenitisclearthatwheretheseorganshave
　　notbeenremoved，thepresenceofthemdeterminestheoccurrenceofthese
　　variouschangesofdevelopment，anddoubtlessmanyminoroneswhichareunobtrusive。
　　Herethefactthatonecauseproducesmanyeffectsinthecourseoforganic
　　evolutionisindisputable。Doubtlessweare，andmustevercontinue，unable
　　toconceivethosemysteriouspropertieswhichmakethegermwhensubject
　　tofitinfluencesundergothespecialchangesinitiating，andmainlyconstituting，
　　thetransformationsofanunfoldingorganism;thoughwemayconsistently
　　supposethattheyrepresentaninfiniteseriesofinheritedmodifications
　　consequentontheinstabilityofthehomogeneous，themultiplicationofeffects，
　　andonefurtherfactorstilltobesetforth。Allherecontendedisthat，
　　givenagermpossessingthesemysteriousproperties，theevolutionofan
　　organismfromitdepends，inpart，onthatmultiplicationofeffectswhich
　　wehaveseentobeonecauseofevolutioningeneral，sofaraswehaveyettracedit。When，leavingthedevelopmentofsingleplantsandanimals，wepassto
　　thatoftheEarth'sFloraandFauna，thecourseoftheargumentagainbecomes
　　clearandsimple。Though，asbeforeadmitted，thefragmentaryfactsPalaeontology
　　hasaccumulated，donotclearlywarrantusinsayingthat，inthelapseof
　　geologictime，therehavebeenevolvedmoreheterogeneousorganisms，and
　　moreheterogeneousassemblagesoforganisms;yetweshallnowseethatthere
　　musteverhavebeenatendencytowardstheseresults。Weshallfindthat
　　theproductionofmanyeffectsbyonecause，which，asalreadyshown，has
　　beenallalongincreasingthephysicalheterogeneityoftheEarth，hasfurther
　　necessitatedanincreasingheterogeneityofitsinhabitingorganisms，individuallyandcollectively。Anillustrationwillmakethisclear。Supposethatbyupheavals，occurring，astheyareknowntodo，atlong
　　intervals，theEastIndianArchipelagowereraisedintoacontinent，and
　　achainofmountainsformedalongtheaxisofelevation。Bythefirstof
　　theseupheavals，theplantsandanimalsofBorneo，Sumatra，NewGuinea，and
　　therest，wouldbesubjectedtoslightly—modifiedsetsofconditions。The
　　climateofeachwouldbealteredintemperature，inhumidity，andinits
　　periodicalvariations，whilethelocaldifferenceswouldbemultiplied。The
　　modificationswouldeffect，perhapsinappreciably，theentireFloraandFauna
　　oftheregion。Thechangeoflevelwouldentailadditionalmodifications，
　　varyingindifferentspecies，andalsoindifferentmembersofthesamespecies，
　　accordingtotheirdistancefromtheaxisofelevation。Plantsgrowingonly
　　onthesea—shoreinspeciallocalities，mightbecomeextinct。Others，living
　　onlyinswampsofacertainhumidity，would，iftheysurvivedatall，probably
　　undergovisiblechangesofappearance。Whilemoremarkedalterationswould
　　occurinsomeoftheplantsthatspreadoverthelandsnewlyraisedoutof
　　thewater。Theanimalsandinsectslivingonthesemodifiedplants，would
　　themselvesbeinsomedegreemodifiedbychangesoffood，aswellasbychanges
　　ofclimate;andthemodificationswouldbemoremarkedwhere，fromthedwindling
　　ordisappearanceofonekindofplant，analliedkindwaseaten。Inthelapse
　　ofthemanygenerationsarisingbeforethenextupheaval，thesensibleor
　　insensiblealterationsthusproducedineachspecies，wouldbecomeorganized
　　——inalltheraceswhichsurvivedtherewouldbemoreorlessadaptation
　　tothenewconditions。Thenextupheavalwouldsuperinducefurtherorganic
　　changes，implyingwiderdivergencesfromtheprimaryforms;andsorepeatedly。
　　Now，however，observethatthisrevolutionwouldnotbeasubstitutionof
　　athousandmodifiedspeciesforthethousandoriginalspecies;butinplace
　　ofthethousandoriginalspeciestherewouldariseseveralthousandspecies，
　　orvarieties，orchangedforms。Eachspeciesbeingdistributedoveranarea
　　ofsomeextent，andtendingcontinuallytocolonizethenewareaexposed，
　　itsdifferentmemberswouldbesubjecttodifferentsetsofchanges。Plants
　　andanimalsmigratingtowardstheequatorwouldnotbeaffectedinthesame
　　waywithothersmigratingfromit。Thosewhichspreadtowardsthenewshores，
　　wouldundergochangesunlikethechangesundergonebythosewhichspread
　　intothemountains。Thus，eachoriginalraceoforganismswouldbecomethe
　　rootfromwhichdivergedseveralraces，differingmoreorlessfromitand
　　fromoneanother;andwhilesomeofthesemightsubsequentlydisappear，probably
　　morethanonewouldsurviveintothenextgeologicperiod。Notonlywould
　　certainmodificationsbethuscausedbychangesofphysicalconditionsand
　　food，butalso，insomecases，othermodificationscausedbychangesofhabit。
　　Thefaunaofeachisland，peopling，stepbystep，thenewly—raisedtracts，
　　wouldeventuallycomeincontactwiththefaunasofotherislands;andsome
　　membersoftheseotherfaunaswouldbeunlikeanycreaturesbeforeseen。
　　Herbivoresmeetingwithnewbeastsofpreywould，insomecases，beledinto
　　modesofdefenceorescapedifferingfromthosepreviouslyused;andsimultaneously
　　thebeastsofpreywouldmodifytheirmodesofpursuitandattack。Weknow
　　thatwhencircumstancesdemandit，suchchangesofhabitdotakeplacein
　　animals;andweknowthatifthenewhabitsbecomethedominantones，they
　　musteventuallyinsomedegreealtertheorganization。Note，now，afurther
　　consequence。Theremustarisenotsimplyatendencytowardsthedifferentiation
　　ofeachraceoforganismsintoseveralraces;butalsoatendencytothe
　　occasionalproductionofasomewhathigherorganism。Takeninthemass，these
　　divergentvarieties，whichhavebeencausedbyfreshphysicalconditions
　　andhabitsoflife，willexhibitalterationsquiteindefiniteinkindand
　　degree，andalterationsthatdonotnecessarilyconstituteanadvance。Probably
　　inmostcasesthemodifiedtypewillbenotappreciablymoreheterogeneous
　　thantheoriginalone。Butitmustnowandthenoccurthatsomedivision
　　ofaspecies，fallingintocircumstanceswhichgiveitrathermorecomplex
　　experiences，anddemandactionssomewhatmoreinvolved，willhavecertain
　　ofitsorgansfurtherdifferentiatedinproportionatelysmalldegrees——
　　willbecomeslightlymoreheterogeneous。Hence，therewillfromtimetotime
　　ariseanincreasedheterogeneitybothoftheEarth'sfloraandfauna，and
　　ofindividualracesincludedinthem。Omittingdetailedexplanations，and
　　allowingforqualificationswhichcannotherebespecified，itissufficiently
　　clearthatgeologicalmutationshaveallalongtendedtocomplicatetheforms
　　oflife，whetherregardedseparatelyorcollectivelyThatmultiplication
　　ofeffectswhichhasbeenapart—causeofthetransformationoftheEarth's
　　crustfromthesimpleintothecomplex，hassimultaneouslyledtoaparallel
　　transformationoftheLifeuponitssurface。（*）