Andasinthemulticellularplantssointhemulticellularanimals，alike
　　primarycontrastisforthwithrepeatedintheinitialclustersofcells。
　　Producedbytherepeatedfissionsoftheprimitivegerm—cell，eachsuchcluster
　　presentlyformsitselfintoahollowsphere:the"cleavagecavity"
　　beingmanifestlyhomologouswiththecavityoftheVilvox—sphere。*InsimpletypesofMetazoa，asthehydroidpolyps，theblastula，
　　beingthusestablishedinconformitywiththeprimarycontrastofconditions，
　　therepresentlybeginsasecondarydifferentiationwhich，likethatwehave
　　seenintheVolvoxbutinamorepronouncedmanner，answerstothesecondary
　　contrastofconditions;forthissphericalassemblageofcellsbecomesovoid，
　　andbytheaidofitsciliamovesthroughthewaterbroadendforemost:the
　　lapsefromhomogeneityofformbeinginsomecasesmademorepronouncedby
　　theassumptionofasausage—shape。Simultaneouslythecomponentcellsof
　　thetwoendsbecomeunlikeincharacter。Afarmoremarkeddifferentiation，
　　orlapseintogreaterheterogeneity，isseenwhenthissingle—layeredspheroid
　　ofciliatedcellsischangedintoadouble—layeredspheroidbyintroversion
　　ofoneside:asackwiththemouthsewnupandthebottomthrustinasfar
　　asitwillgo，servingtoillustratetherelationsofparts。Henceresults
　　thegastrulawithitsectodermandendoderm;severallyplayingcontrasted
　　partsinsubsequentdevelopment。Sothatatsuccessivestagesthereisrepeated
　　thisriseofacontrastofstructuresansweringtoacontrastofconditions
　　——thatwhichoccursinthesimplecell，thatwhichoccursinthehollowsphereofsuchcells，andthatwhichoccursinthedouble—walledsphere。Illustrationspresentingthelawunderanotheraspect——onefromeach
　　organickingdom——areinstructive。TheciliatedgermorplanulaofaZoophyte
　　which，duringitslocomotivestage，isdistinguishableonlyintoouterand
　　innertissues，nosoonerbecomesfixedthanitsupperendbeginstoassume
　　adifferentstructurefromitslower。Thedisc—shapedgemmaeoftheMarchantia，
　　originallyalikeonbothsurfaces，andfallingatrandomwitheitherside
　　uppermost，immediatelybegintodeveloprootletsontheirundersidesand
　　stomataontheiruppersides:afactprovingbeyondquestion，thatthisprimarydifferentiationisdeterminedbythisfundamentalcontrastofconditions。Ofcourseinthegermsofhigherorganisms，themetamorphosesimmediately
　　duetotheinstabilityofthehomogeneous，aresoonmaskedbythosedueto
　　theassumptionofthehereditarytype。Evenintheearlystagesabovedescribed
　　therearetobetracedmodificationsthusoriginating。Evenbeforetheprimary
　　cell—multiplicationbegins，thereissaidtobeanobservabledistinction
　　betweenthetwopolesoftheegg—cell，foreshadowingthedifferentgerm—layers。
　　Ofcourseasdevelopmentprogressesassumptionofthetransmittedtypeof
　　structurequicklyobscurestheseprimarylapsesfromhomogeneity;though
　　forsometimethefundamentalrelationsofinnerandouterarerecognizable
　　inthedifferentiations。Butwhathasbeensaidsufficestoestablishthe
　　allegedgeneraltruth。Itisenoughthatincipientorganisms，settingout
　　fromrelativelyhomogeneousarrangements，forthwithbegintofallintorelatively
　　heterogeneousones。Itisenoughthatthemostconspicuousdifferentiations
　　whichtheydisplay，correspondtothemostmarkeddifferencesofconditions
　　towhichtheirpartsaresubject。Itisenoughthatthehabitualcontrast
　　betweenoutsideandinside，whichweknowisproducedininorganicmasses
　　byunlikenessofexposuretoincidentforces，isparalleledbythefirstcontrastwhichmakesitsappearanceinallorganicmasses。Itremainstopointoutthatintheassemblageoforganismsconstituting
　　aspecies，theprincipleenunciatedisnolesstraceable。Wehaveabundant
　　materialsfortheinductionthateachspecieswillnotremainuniform——
　　iseverbecomingtosomeextentmultiform;andthereisgroundforthededuction
　　thatthislapsefromhomogeneitytoheterogeneityiscausedbythesubjection
　　ofitsmemberstounlikecircumstances。Tendingevertospreadfromitsoriginal
　　habitatintoadjacenthabitats，eachspeciesmusthaveitsperipheralparts
　　subjecttosetsofforcesunlikethosetowhichitscentralpartsaresubject，
　　andsomusttendtohaveitsperipheralmembersmadedifferentfromitscentralmembers。§153。Amongmentalphenomenafullestablishmentoftheallegedlaw
　　wouldinvolveananalysistooextensivefortheoccasion。Toshowsatisfactorily
　　howstatesofconsciousness，relativelyhomogeneous，becomeheterogeneous
　　throughdifferencesinthechangeswroughtbydifferentexternalforces，
　　wouldrequireustotraceouttheorganizationofearlyexperiences。Withouthereattemptingthisitmustsufficetosetdowntheconclusionstobedrawn。Thedevelopmentofintelligenceis，underoneofitschiefaspects，a
　　classifyingoftheunlikethingspreviouslyconfoundedtogether——aformation
　　ofsub—classesandsub—sub—classes，untiltheonceconfusedaggregateof
　　objectsknown，isresolvedintoanaggregatewhichunitesgreatheterogeneity
　　amongitsmultipliedgroups，withcompletehomogeneityamongthemembers
　　ofeachgroup。Onfollowingthroughascendinggradesofcreatures，thegenesis
　　ofthatvaststructureofknowledgeacquiredbysight，weseethatinthe
　　firststage，whereeye—speckssufficeonlyfordiscriminatinglightfrom
　　darkness，therecanbenoclassificationsofobjectsseen，savethosebased
　　onthemannerinwhichlightisobstructed，andthedegreeinwhichitis
　　obstructed。Bysuchundevelopedvisualorgans，theshadowsperceivedwould
　　bemerelydistinguishedintothoseofthestationaryobjectswhichthecreature
　　passedduringitsownmovements，andthoseofthemovingobjectswhichcame
　　nearwhileitwasatrest;sothattheextremelygeneralclassificationof
　　visiblethingsintostationaryandmoving，wouldbetheearliestformed。
　　Akindredstepfollows。Whilethesimplesteyescannotdistinguishbetween
　　anobstructionoflightcausedbyasmallobjectcloseto，andanobstruction
　　causedbyalargeobjectatsomedistance，eyesalittlemoredevelopedcan
　　distinguishthem;whencemustresultavaguedifferentiationoftheclass
　　ofmovingobjectsintothenearerandthemoreremote。Furtherdevelopments
　　whichmakepossibleabetterestimationofdistancesbyadjustmentofthe
　　opticaxes，andthosewhich，throughenlargementandsubdivisionoftheretina，
　　makepossiblethediscriminationofshapes，mustgivegreaterdefiniteness
　　totheclassesalreadyformed，andsubdividetheseintosmallerclasses，
　　consistingofobjectslessunlike。Ineveryinfantmaybetracedtheanalogous
　　transformationofaconfusedaggregateofimpressionsofsurroundingthings，
　　notrecognizedasdifferingintheirdistances，sizes，andshapes，intoseparate
　　classesofthingsunlikeoneanotherintheseandvariousotherrespects。
　　Andinbothcasesthechangefromthisfirstindefinite，incoherent，and
　　comparativelyhomogeneousconsciousness，toadefinite，coherent，andheterogeneous
　　one，isduetodifferencesintheactionsofincidentforcesontheorganism。
　　Thesebriefindicationsmustsuffice。Probablytheywillgiveadequateclue
　　toanargumentbywhicheachreadermaysatisfyhimselfthatthecourseof
　　mentalevolutionoffersnoexceptiontothegenerallaw。Infurtheraidof
　　suchanargument，Iwillhereaddanillustrationwhichiscomprehensibleapartfromtheprocessofmentalevolutionasawhole。Ithasbeenremarked（IamtoldbyColeridge）thatwiththeadvanceof
　　language，wordswhichwereoriginallyalikeintheirmeaningsacquireunlike
　　meanings——achangeheexpressedbytheformidableword"de—synonymization。"
　　Amongindigenouswordsthislossofequivalencecannotbeclearlyshown;
　　becauseinthemthedivergencesofmeaningbeganbeforethedawnofliterature。
　　Butamongwordsthathavebeencoined，oradoptedfromotherlanguages，since
　　thewritingofbookscommenced，itisdemonstrable。Bytheolddivines，miscreant
　　wasusedinitsetymologicalsenseofunbeliever;butinmodernspeechit
　　hasentirelylostthissense。Similarlywithevil—doerandmalefactor。Exactly
　　synonymousasthesearebyderivation，theyarenolongersynonymousbyusage。
　　Byamalefactorwenowunderstandaconvictedcriminal，whichisfarfrom
　　beingtheacceptationofevil—doer。TheverbproducebearsinEuclidits
　　primarymeaning——toprolongordrawout;butthenowlargely—developed
　　meaningsofproduce，havelittleincommonwiththemeaningsofprolong，
　　ordrawout。IntheChurchofEnglandliturgyanoddeffectnowresultsfrom
　　theoccurrenceofpreventinitsoriginalsense——tocomebefore，instead
　　ofitsmodernspecializedsense——tocomebeforewiththeeffectofarresting。
　　Butthemostconclusivecasesarethoseinwhichthecontrastedwordsconsist
　　ofthesamepartsdifferentlycombined，asingounderandundergo。Wego
　　underatree，andweundergoapain。Butthough，ifanalyticallyconsidered，
　　themeaningswouldbethesamewerethewordstransposed，habithassofar
　　modifiedtheirmeaningsthatwecouldnotwithoutabsurdityspeakofundergoing
　　atreeandgoingunderapain。Manysuchinstancesshowthatbetweentwo
　　wordswhichareoriginallyoflikeforce，anequilibriumcannotbemaintained。
　　Unlesstheyaredailyusedinexactlyequaldegrees，inexactlysimilarrelations
　　（whichisinfinitelyimprobable），therenecessarilyariesahabitofassociating
　　oneratherthantheotherwithparticularacts，orobjects。Suchahabit
　　oncecommenced，becomesconfirmed;andgraduallytheirhomogeneityofmeaningdisappears。Shouldanydifficultybefeltinunderstandinghowthesementalchanges
　　exemplifyalawofphysicaltransformationsthatarewroughtbyphysical
　　forces，itwilldisappearoncontemplatingactsofmindasnervousfunctions。
　　Itwillbeseenthateachlossofequilibriumaboveinstanced，isaloss
　　offunctionalequalitybetweensometwoelementsofthenervoussystem。And
　　itwillbeseenthat，asinothercases，thislossoffunctionalequalityisduetodifferencesintheincidenceofforces。§154。Massesofmen，incommonwithallothermasses，showalike
　　proclivitysimilarlycaused。Smallcombinationsandlargesocietiesequally
　　manifestit;andintheone，asintheother，bothgovernmentalandindustrial
　　differentiationsareinitiatedbyit。Letusglanceatthefactsundertheseheads。Abusiness—partnership，balancedastheauthoritiesofitsmembersmay
　　theoreticallybe，presentlybecomesaunioninwhichtheauthorityofone
　　partneristacitlyrecognizedasgreaterthanthatoftheotherorothers。
　　Thoughtheshareholdershavegivenequalpowerstothedirectorsoftheir
　　company，inequalitiesofpowersoonariseamongthem;andoftenthesupremacy
　　ofsomeonedirectorgrowssomarked，thathisdecisionsdeterminethecourse
　　whichtheboardtakes。Norinassociationsforpolitical，charitable，literary，
　　orotherpurposes，dowefailtofindalikeprocessofdivisionintodominant
　　andsubordinateparties;eachhavingitsleader，itsmembersoflessinfluence，
　　anditsmassofuninfluentialmembers。Theseminorinstancesinwhichunorganized
　　groupsofmen，standinginhomogeneousrelations，maybewatchedgradually
　　passingintoorganizedgroupsofmenstandinginheterogeneousrelations，
　　giveuskeytosocialinequalities。Barbarousandcivilizedcommunitiesare
　　alikecharacterizedbyseparationintoclasses，aswellasbyseparation
　　ofeachclassintomoreimportantandlessimportantunits;andthisstructure
　　isthegradually—consolidatedresultofaprocesslikethatdailyexemplified
　　intradingandothercombinations。Solongasmenareconstitutedtoact
　　ononeanother，eitherbyphysicalforceorbyforceofcharacterthestruggles
　　forsupremacymustfinallybedecidedinfavourofsomeclassorsomeone;
　　andthedifferenceoncecommencedmusttendtobecomeevermoremarked。Its
　　unstableequilibriumbeingdestroyed，theuniformmustgravitatewithincreasing
　　rapidityintothemultiform。Andsosupremacyandsubordinationmustestablish
　　themselves，asweseetheydo，throughoutthewholestructureofasociety，
　　fromthegreatclass—divisionspervadingitsentirebody，downtovillage
　　cliques，andevendowntoeveryposseofschoolboys。Probablyitwillbe
　　objectedthatsuchchangesresult，notfromthehomogeneityoftheoriginal
　　aggregations，butfromtheirnon—homogeneity——fromcertainslightdifferences
　　existingamongtheirunitsattheoutset。Thisisdoubtlesstheproximate
　　cause。Instrictness，suchchangesmustberegardedastransformationsof
　　therelativelyhomogeneousintotherelativelyheterogeneous。Butanaggregation
　　ofmenabsolutelyalikeintheirendowments，wouldeventuallyundergoasimilar
　　transformation。Forintheabsenceofuniformityinthelivesseverallyled
　　bythem——intheiroccupations，physicalconditions，domesticrelations，
　　andtrainsofthoughtandfeeling——theremustarisedifferencesamongthem;
　　andthesemusteventuallyinitiatesocialdifferentiations。Eveninequalities
　　ofhealthcausedbyaccidentswill，byentailinginequalitiesofphysical
　　andmentalpower，disturbtheexactbalanceofmutualinfluencesamongtheunits;andthebalanceoncedisturbed，willinevitablybelost。Turningtotheindustrialorganization，andnotingthatitsdivisioninto
　　regulativeandoperativeisprimarilydetermined，likethepreceeding，by
　　differencesofpower（womenandslavesbeingthefirstworkingclasses）;
　　admitting，too，thatevenamongsavagessomesmallspecializationsarise
　　fromindividualaptitudes;wegoontoobservethatthelargeindustrial
　　divisionsintowhichsocietiesgravitate，areduetounlikenessesofexternal
　　circumstances。Suchdivisionsareabsentuntilsuchunlikenessesareestablished。
　　Nomadictribesdonotpermanentlyexposeanygroupsoftheirmemberstospecial
　　localconditions;nordoesastationarytribe，whenoccupyingonlyasmall
　　area，maintainfromgenerationtogenerationmarkedcontrastsinthelocal
　　conditionsofitsmembers;andinsuchtribestherearenodecidedeconomic
　　differentiations。Butacommunitywhich，byconquest，orotherwise，hasoverspread
　　alargetract，andhasbecomesofarsettledthatitsmembersliveanddie
　　intheirrespectivedistricts，keepsitsseveralsectionsindifferentcircumstances;
　　andthentheynolongerremainalikeintheiroccupations。Thosewholive
　　dispersedcontinuetohuntorcultivatetheearth;thosewhospreadtothe
　　sea—shorefallintomaritimeoccupations;whiletheinhabitantsofsomespot
　　chosen，perhapsforitscentrality，asoneofperiodicassemblage，become
　　traders，andatownspringsup。Intheadaptationsofthesesocialunits
　　totheirrespectivefunctions，weseeaprogressfromuniformitytomultiformity
　　causedbyunlikeincidenceofforces。Laterintheprocessofsocialevolution
　　theselocaladaptationsaregreatlymultiplied。Differencesinsoilandclimate，
　　causetheruralinhabitantsindifferentpartsofthekingdomtohavetheir
　　occupationspartiallyspecialized，andtobecomeknownaschieflyproducing
　　cattle，orsheep，orwheat，oroats，orhops，orfruit。Peoplelivingwhere
　　coal—fieldsarediscoveredaretransformedintocolliers;Cornishmentake
　　tominingbecauseCornwallismetalliferous;andiron—manufactureisthe
　　dominantindustrywhereiron—stoneisplentiful。Liverpoolhastakentoimporting
　　cotton，becauseofitsproximitytothedistrictwherecotton—goodsaremade;
　　andforanalogousreasonsHullhasbecomethechiefportatwhichforeign
　　woolsarebroughtin。Thusingeneralandindetail，industrialheterogeneities
　　ofthesocialorganismprimarydependonlocalinfluences。Thosedivisions
　　oflabourwhich，underanotheraspect，wereinterpretedasduetothesetting
　　upofmotioninthedirectionsofleastresistance（§80），arehereinterpreted
　　asduetodifferencesintheincidentforces;andthetwointerpretations
　　arequiteconsistentwitheachother。Forthatwhichineachdeterminesthe
　　directionofleastresistance，isthedistributionoftheforcestobeovercome;
　　andhenceunlikenessesofdistributioninseparatelocalities，entailsunlikenessesinthelinesofhumanactionsinthoselocalities——entailsindustrialdifferentiations。§155。Ithasstilltobeshownthatthisgeneraltruthisdemonstrable
　　apriori——thattheinstabilityofthehomogeneousisacorollaryfromthe
　　persistenceofforce。Alreadythishasbeentacitlyimplied，buthereitwillbepropertoexpandthetacitimplicationintodefiniteproof。Onstrikingamassofmatterwithsuchforceaseithertoindentitor
　　makeitflytopieces，weseeboththattheblowaffectsdifferentlyits
　　differentparts，andthatthedifferencesareconsequentontheunlikerelations
　　ofitspartstotheforceimpressed。Thepartstruckisdrivenintowards
　　thecentreofthemass。Itthuscompresses，andtendstodisplace，themore
　　centrallysituatedportions。These，however，cannotbecompressedorthrust
　　outoftheirplaceswithoutpressingonsurroundingportions。Andwhenthe
　　blowisviolentenoughtofracturethemass，wesee，intheradialdispersion
　　ofthefragments，thattheoriginalmomentumhasbeendividedintonumerous
　　minormomenta，unlikeintheirdirections。Weseethatthepartsaredifferently
　　affectedbythedisruptiveforce，becausetheyaredifferentlyrelatedto
　　itintheirdirectionsandattachments——thattheeffectsbeingthejoint
　　productsoftheforceandtheconditionscannotbealikeinpartswhichare
　　differentlyconditioned。Abodyonwhichradiantheatisfalling，exemplifies
　　thistruthstillmoreclearly。Takethesimplestcase——thatofasphere。
　　Whilethepartnearesttotheradiatingcentrereceivestheraysatright
　　angles，theraysstriketheotherpartsoftheexposedsideatallangles
　　from90°downto0°。Themolecularvibrationspropagatedthrough
　　themassfromthesurfacewhichreceivestheheat，proceedinwardsatangles
　　differingforeachpoint。Further，theinteriorpartsreachedbythevibrations
　　proceedingfromallpointsoftheheatedside，mustbedissimilarlyaffected
　　inproportionastheirpositionsaredissimilar。Sothatwhethertheybe
　　ontherecipientarea，inthemiddle，orattheremoteside，theconstituentmoleculesarethrownintostatesofvibrationmoreorlessunlikeoneanother。Butnow，whatistheultimatemeaningoftheconclusionthataforceproduces
　　differentchangesthroughoutauniformmass，becausethepartsofthemass
　　standindifferentrelationstotheforce？Fullytounderstandthis，wemust
　　contemplateeachpartassimultaneouslysubjecttootherforces——those
　　ofgravitation，ofcohesion，molecularmotion，etc。Theeffectwroughtby
　　anadditionalforce，mustbearesultantofitandtheforcesalreadyin
　　action。Iftheforcesalreadyinactionontwopartsofanyaggregate，are
　　differentintheirresultantdirections，theeffectsproducedonthesetwo
　　partsbyequaladditionalforcesmustbedifferentintheirdirections。Why
　　musttheybedifferent？Becausesuchunlikenessasexistsbetweenthetwo
　　setsoffactors，ismadebythepresenceintheoneofsomespecially—directed
　　forcethatisnotpresentintheother;andthatthisforcewillproduce
　　aneffect，renderingthetotalresultintheonecaseunlikethatinthe
　　other，isanecessarycorollaryfromthepersistenceofforce。Stillmore
　　manifestdoesitbecomethatthedissimilarly—placedpartsofanyaggregate
　　mustbedissimilarlymodifiedbyanincidentforce，whenwerememberthat
　　thequantitiesoftheincidentforcetowhichtheyareseverallysubject，
　　arenotequal，asabovesupposed，butarenearlyalwaysunequal。Lookagain
　　attheaboveexamples。Theamountsofanyexternalradiantforcewhichthe
　　differentpartsofanaggregatereceive，arewidelycontrasted:wehavethe
　　contrastbetweenthequantityfallingonthesidenexttheradiatingcentre，
　　andthequantity，orrathernoquantity，fallingontheoppositeside;we
　　havecontrastsinthequantitiesreceivedbydifferently—placedareason
　　theexposedside;andwehaveendlesscontrastsbetweenthequantitiesreceived
　　bythevariouspartsoftheinterior。Similarlywhenmechanicalforceis
　　expendedonanyaggregate，eitherbycollision，continuedpressure，ortension，
　　theamountsofstraindistributedthroughoutthemassaremanifestlyunlike
　　forunlikepositions。Anditisobviousthatordinarychemicalactionaffects
　　surfacemorethancentre，andoftenonepartofthesurfacemorethananother。
　　Buttosaythedifferentpartsofanaggregatereceivedifferentquantities
　　ofanyforcecapableofchangingthem，istosaythatiftheywerebefore
　　homogeneoustheymustberenderedtoaproportionateextentheterogeneous;
　　since，forcebeingpersistent，thedifferentquantitiesofitfallingon
　　thedifferentparts，mustworkinthemdifferentquantitiesofeffect—different
　　changes。Yetonemorekindreddeductionisrequiredtocompletetheargument。
　　Evenapartfromtheactionofanyexternalforce，theequilibriumofahomogeneous
　　aggregatemustbedestroyedbytheunequalactionsofitspartsononeanother。
　　Thatmutualinfluencewhichproducesaggregation（nottomentionothermutual
　　influences）mustworkdifferenteffectsonthedifferentparts;sincethey
　　areseverallyexposedtoitinunlikeamountsanddirections。Thiswillbe
　　clearlyseenonrememberingthattheportionsofwhichthewholeismade
　　up，maybeseverallyregardedasminorwholes;thatoneachoftheseminor
　　wholes，theactionoftheentireaggregatethenbecomesanexternalincident
　　force;thatsuchexternalincidentforcemust，asaboveshown，workunlike
　　changesinthepartsofanysuchminorwhole;andthatiftheminorwholes
　　areseverallythusrenderedheterogeneous，theentireaggregateisrenderedheterogeneous。Theinstabilityofthehomogeneousisthusdeduciblefromthatprimordial
　　truthwhichunderliesourintelligence。Onestablehomogeneityonly，ishypothetically
　　possible。Ifcentresofforce，absolutelyuniformintheirpowers，werediffused
　　withabsoluteuniformitythroughunlimitedspace，theywouldremaininequilibrium。