andwouldsorenderittothatextentheterogeneous。Takeapieceofred—hot
　　matter，andhoweverevenlyheateditmayatfirstbe，itwillquicklycease
　　tobeso:theexterior，coolingfasterthantheinteriorwillbecomedifferent
　　fromitintemperature。Andthelapseintoheterogeneityoftemperature，
　　soobvious。inthisextremecase，takesplacemoreorlessinthecasesof
　　allsurroundingobjects，whichareeverbeingwarmedorcooled。Theaction
　　ofchemicalforcessuppliesotherillustrations。Exposeafragmentofmetal
　　toairorwater，andincourseoftimeitwillbecoatedwithafilmofoxide，
　　carbonate，orothercompound:itsouterpartswillbecomeunlikeitsinner
　　parts。Oftentheheterogeneityproducedbytheactionsofchemicalforces
　　onthesurfacesofmasses，isnotstriking，becausethechangedportions
　　aresoonwashedaway，orotherwiseremoved。Butifthisbepreventedcomparatively
　　complexstructuresresult。Insomequarriesoftrap—rocktherearestriking
　　examples。Notunfrequentlyapieceoftrapmaybefoundreduced，bytheaction
　　oftheweather，toanumberofloosely—adherentcoats，likethoseofanonion。
　　Wheretheblockhasbeenundisturbed，wemaytracethewholeseriesofthese，
　　fromtheangular，irregularouterone，throughsuccessivelyincludedones
　　inwhichtheshapebecomesgraduallyrounded，endingatlengthinaspherical
　　nucleus。Oncomparingtheoriginalmassofstonewiththisgroupofconcentric
　　coats，eachdifferingfromtherestinform，andprobablyinthestateof
　　decompositionithasarrivedat，wegetamarkedillustrationofthemultiformity
　　towhich，inlapseoftime，auniformbodymaybebroughtbyexternalchemical
　　action。Theinstabilityofthehomogeneousisequallyseeninthechanges
　　setupthroughouttheinteriorofamass，whenitconsistsofunitsthat
　　arenotrigidlyboundtogether。Themoleculesofaslowly—settlingprecipitate
　　donotremainseparate，andequablydistributedthroughthefluidinwhich
　　theymaketheirappearance。Theyaggregateeitherintocrystallinegrains
　　orintoflocculi;andwherethemassoffluidisgreatandtheprocessprolonged，
　　theseflocculidonotcontinueequi—distant，butasSembleintogroups。That
　　istosay，thereisadestructionofthebalanceatfirstsubsistingamong
　　thediffusedparticles，andalsoofthebalanceatfirstsubsistingamongthegroupsintowhichtheseparticlesunite。Theinstabilitythusvariouslyillustratedisconsequentonthefactthat
　　theseveralpartsofanyhomogeneousaggregateareexposedtodifferentforces
　　——forceswhichdiffereitherinkindoramount;andareofnecessitydifferently
　　modified。Therelationsofoutsideandinside，andofcomparativenearness
　　ofthepartstoneighbouringsourcesofinfluence，implythereceptionof
　　influencesthatareunlikeinquantityorquality，orboth:unlikechanges，nowtemporarynowpermanent，beingcaused。Forlikereasonstheprocessmustrepeatitselfineachofthecomponent
　　massesofunitsthataredifferentiatedbythemodifyingforces。Eachof
　　theseminorgroups，likethemajorgroup，mustgradually，inobedienceto
　　theunlikeinfluencesactingonit，loseitsbalanceofparts，andpassfrom
　　auniformintoamultiformstate。Andsooncontinuously。Whence，indeed，
　　itfollowsthatnotonlymustthehomogeneouslapseintonon—homogeneous，
　　butthemorehomogeneousmusttendevertobecomelesshomogeneous。Ifany
　　givenwhole，insteadofbeingabsolutelyuniformthroughout，consistofparts
　　distinguishablefromoneanother——ifeachoftheseparts，whilesomewhat
　　unlikeotherparts，isuniformwithinitself;then，eachofthembeingin
　　unstableequilibrium，itfollowsthatwhilethechangessetupwithinit
　　mustrenderitmultiform，theymustatthesametimerenderthewholemore
　　multiformthanbefore。Thegeneralprinciple，nowtobefollowedoutinits
　　applications，isthussomewhatmorecomprehensivethanthetitleofthechapterimplies。Nodemurrertotheconclusionsdrawn，canbebasedonthetruththatperfect
　　homogeneitynowhereexists;since，whetherthatstatewithwhichwecommence
　　beorbenotoneofperfecthomogeneity，theprocessmustequallybetowardsarelativeheterogeneity。§150。Thestarsaredistributedwithathreefoldirregularity。There
　　isfirstthemarkedcontrastbetweentheMilkyWayandotherpartsofthe
　　heavens，inrespectofthequantitiesofstarswithingivenvisualareas。
　　TherearesecondarycontrastsoflikekindintheMilkyWayitself，which
　　hasitsthickandthinplaces;aswellasthroughoutthecelestialspaces
　　ingeneral，whicharemorecloselystrewninsomeregionsthaninothers。
　　Andthereisathirdorderofcontrastsproducedbytheaggregationofstars
　　intosmallclusters。Besidesthisheterogeneityinthedistributionofstars，
　　consideredwithoutdistinctionsofkind，afurtherheterogeneityisdisclosed
　　whentheyareclassifiedbytheirdifferencesofcolour，whichanswerto
　　differencesofphysicalconstitution。Whileyellowstarsarefoundinall
　　partsoftheheavens，redandbluestarsarenotso:therearewideregions
　　inwhichbothredandbluestarsarerare;thereareregionsinwhichthe
　　blueoccurinconsiderablenumbers，andthereareotherregionsinwhich
　　theredarecomparativelyabundant。Yetonemoreirregularityoflikesignificance
　　ispresentedbythenebulae。Thesearenotdispersedwithanythinglikeuniformity，
　　butarefarmorenumerousaroundthepolesofthegalacticcirclethanintheneighbourhoodofitsplane。Noonewillexpectthatanythinglikeadefiniteinterpretationofthis
　　structurecanbegivenonthehypothesisofEvolution，oranyotherhypothesis。
　　Suchaninterpretationwouldimplysomereasonableassumptionrespecting
　　thepre—existingdistributionofthestellarmatterandofthematterforming
　　nebulae，andwehavenowarrantforanyassumption。Ifweallowimagination
　　torangebackthroughantecedentPossibilitiesandprobabilities，wesee
　　ittobeunlikelythathomogeneousmatterfilledthespacewhichourSidereal
　　Systemnowfills，atatimeimmediatelyprecedingitsinitiation。Rather
　　theevidencewhichtheheavenspresentimpliesthatthedistributionout
　　ofwhichthepresentdistributionarose，wasirregularinallrespects。Though
　　certaintraitsofourgalaxysuggestthatithasavagueindividuality，and
　　that，alongwiththeirspecialmotions，itsstarshavesomegeneralmotion;
　　yettheevidenceforcesonustheconclusionthatmanyvarietiesofchanges
　　havebeensimultaneouslygoingoninitsdifferentparts。Wefindnebulae
　　inallstagesofconcentration，star—clustersvariouslycondensed，groups
　　oflargerstarsapproximatingindifferentdegrees，aswellasregionslike
　　thosewhichthenubeculaeoccupy，presentingcomplexstructuresandapparently
　　activechanges。Themostwhichcanbesaidrespectingthistotaldistribution
　　isthat，subjectasallpartsofourSiderealSystemaretothelawofgravitation，
　　theheterogeneitiesitexhibits，everywhereimplyingaprogressingconcentration，
　　thatis，integration，pointbackwardtoalessheterogeneousstateandpoint
　　forwardtoamoreheterogeneousstate。But，leavingasidethistootranscendent
　　question，wemaywithoutunduerashnessconsiderfromtheevolutionpoint
　　ofviewthechangestobeanticipatedinoneofthosecollectionsofmatter
　　describedasadiffusednebulosity，oroneofthosemoredistinctonesof
　　whichtheoutlyingpartsarecomparedtowispsofcloudblownaboutbythe
　　wind。Theonlyevolutionalprocesswhichcanatfirstbedisplayedisthe
　　primaryoneofintegration——thegatheringtogetherthroughmutualattraction
　　oftheparts;forinthisearlystageinwhichindefinitenessandincoherence
　　aresofullyexemplified，theredoesnotyetexistsuchanaggregateasis
　　capableofexhibitingsecondaryre—distributions:wehaveonlythedispersed
　　componentsofsuchanaggregate。Contemplating，then，onlytheprocessof
　　integration，wemay，withoutaskinganythingabouttheprevioushistoryof
　　anirregularnebula，safelyassumethatitspartshavetheirrespectiveproper
　　motions;forthechancesareinfinitytooneagainstastateofrestrelatively
　　tooneanother。Further，thechancesareinfinitytooneagainsttheirproper
　　motionsbeingsuchthatduringconcentrationtheywillcanceloneanother:
　　themotionofsomepart，ortheresultantofthemotionsofseveralparts，
　　willconstituteapropermotiondistinctfromthatwhichmutualgravitation
　　generates——amotionwhich，unlessjustcounterbalancedbyanoppositeone
　　（againaninfiniteimprobability）willgeneraterotation。Itmay，indeed，
　　bearguedthat，apartfromanypre—existingpropermotionsofitsparts，
　　anebulousmass，ifirregular，willacquirerotationwhileintegrating;since
　　eachoutlyingfragment，arrivingaftertheresthavebeengatheredtogether，
　　isinfinitelyunlikelytofallintothemassinsuchamannerthatitsmotion
　　willbeentirelycancelledbyresistance;but，fallingintoitsoastobe
　　deflectedlaterally，willhaveitsmotionofapproachsochangedindirection
　　astobecomeinpartamotionofrevolution:aresultantofallsuchmotions，
　　largelyconflicting，beinganeventualrotationofthemass。Itmustnot，
　　however，beassumedthatthiswillnecessarilybetherotationofasolitary
　　aggregate。ThegreatnebulainAndromedadoesnotappearonthewaytoform
　　asinglebody;andisanadvancedspiralofwhichthethatinCanesVenatici
　　outerpartshaveatangentialmotiontoogreattopermitoftheirbeingdrawn
　　intothecentre。Rathertheapparentimplicationofthestructureisthat
　　therewillbeformedaclusterofmassesrevolvingroundacommoncentre
　　ofgravity。Suchcases，joinedwiththoseoftheannularnebula，suggest
　　thatoftentheprocessesofintegrationresultincompoundstructures，various
　　intheirkinds，whileinothercases，andperhapsmostfrequently，singlemassesofrotatingnebulousmatterareformed。Ignoringallsuchpossibilitiesandprobabilities，however，andlimiting
　　ourattentiontothatformofthenebularhypothesiswhichregardsthesolar
　　systemashavingresultedfromarotatingspheroidofdiffusedsubstance;
　　letusconsiderwhatconsequencetheinstabilityofthehomogeneousnecessitates。
　　Beingoblateinfigure，unlikeinthedensitiesofitscentreandsurface，
　　unlikeintheirtemperatures，andprobablyunlikeintheangularvelocities
　　ofitsparts，suchamasscannotbecalledhomogeneous;andanyfurtherchanges
　　exhibitedbyitcanillustratethegenerallaw，onlyasbeingchangesfrom
　　amorehomogeneoustoalesshomogeneousstate。Justnotingthatoneofthese
　　changesistheincreasingoblatenessofform，letusgoontoobservethose
　　whicharetobefoundinthetransformationsofsuchofitspartsasare
　　atfirsthomogeneouswithinthemselves。Ifweaccepttheconclusionthat
　　theequatorialportionofthisrotatingandcontractingspheroidwill，at
　　successivestages，haveacentrifugalforcegreatenoughtopreventnearer
　　approachtothecentreofrotation，andwillsobeleftbehind;weshall
　　find，inthefateofthedetachedring，anexemplificationoftheprinciple
　　wearefollowingout。Consistingofgaseousmattersucharing，evenifuniform
　　atthetimeofitsdetachment，couldnotcontinueso。Intheabsenceofequality
　　amongtheforces，internalandexternal，actingonit，theremustbeapoint
　　orpointsatwhichthecohesionofitspartswouldbelessthanelsewhere
　　——apointorpointsatwhichrupturewouldthereforetakeplace。Theoriginal
　　assumptionwasthattheringwouldruptureatoneplaceonly，andwouldthen
　　collapseonitself。Butthiswasamorethanquestionableassumption:such，
　　atleast，IknowtohavebeentheopinionofthelateSirJohnHerschel。
　　Sovastaring，consistingofmatterhavingsuchfeeblecohesion，mustbreak
　　upintomanyparts。Nevertheless，appealtoanotherhighauthority——the
　　lateSirG。B。Airy——yieldedverificationforthebeliefthattheultimate
　　resultwhichLaplacepredictedwouldtakeplace。Andhereisfurnisheda
　　furtherillustrationoftheinstabilityofthehomogeneous。Forevensupposing
　　themassesofnebulousmatterintowhichsucharingseparated，weresomuch
　　alikeintheirsizesanddistancesastoattractoneanotherwithexactly
　　equalforces（whichisinfinitelyimprobable）;yettheunequalactionsof
　　externaldisturbingforceswouldinevitablydestroytheirequilibrium——
　　therewouldbeoneormorepointsatwhichadjacentmasseswouldbeginto
　　partcompany。Separation，oncecommenced，wouldwithacceleratingspeedlead
　　toagroupingofthemasses。Alikeresultwouldeventuallytakeplacewiththegroupsthusformed;untiltheyatlengthaggregatedintoasinglemass。§151。Alreadysomanyreferenceshavebeenmadetotheformation
　　ofacrustovertheoriginallyincandescentEarth，thatitmaybethought
　　superfluousagaintonameit。Ithasnot，however，beenthusfarconsidered
　　inconnexionwiththegeneralprincipleunderdiscussion。Hereitmustbe
　　notedasanecessaryconsequenceoftheinstabilityofthehomogeneous。In
　　thiscoolingandsoldificationoftheEarth'ssurface，wehaveoneofthe
　　simplest，aswellasoneofthemostimportant，instancesofthatchange
　　fromauniformtoamultiformstatewhichoccursinanymassthroughexposure
　　ofitscomponentpartstounlikeconditions。Tothedifferentiationofthe
　　Earth'sexteriorfromitsinterior，thusbroughtabout，wemustaddoneof
　　themostconspicuousdifferentiationswhichtheexterioritselfafterwards
　　undergoes，asbeingsimilarlybroughtabout。Weretheforcestowhichthe
　　surfaceoftheEarthissubject，alikeinalldirections，therewouldbe
　　noreasonwhycertainofitspartsshouldbecomepermanentlyunliketherest。
　　Butbeingunequallyexposedtothechiefexternalcentreofforce——the
　　Sun——itsmaindivisionsbecomeunequallymodified。Whilethecrustthickens
　　andcools，therearisesthatcontrast，nowsodecided，betweenthepolarandequatorialregions。AlongwiththesemostmarkedphysicaldifferentiationsoftheEarth，there
　　havebeengoingonnumerouschemicaldifferentiations，admittingofsimilar
　　interpretation。Leavingasideallspeculationsconcerningtheoriginofthe
　　so—calledsimplesubstances，itwillsufficetoshowhowinplaceofthat
　　comparativehomogeneityoftheEarth'scrust，chemicallyconsidered，which
　　musthaveexistedwhenitstemperaturewashigh，therehasarisen，during
　　itscooling，anincreasingchemicalheterogeneity。Letuscontemplatethis
　　changesomewhatindetail。Atanextremeheatthebodieswecallelements
　　cannotcombine。Evenundersuchheatascanbegeneratedartificially，some
　　verystrongaffinitiesyield;andthegreatmajorityofchemicalcompounds
　　aredecomposedatmuchlowertemperatures。Probably，therefore，whenthe
　　Earthwasinitsfirststateofincandescence，therewerenochemicalcombinations。
　　Butwithoutdrawingthisinference，letussetoutwiththeunquestionable
　　factthatthecompoundswhichcanexistatthehighesttemperatures，and
　　whichmustthereforehavebeenthefirstformedastheEarthcooled，are
　　thoseofthesimplestconstitutions。Theprotoxides（includingunderthat
　　headthealkalies，earths，etc。）are，asaclass，themoststablecompounds
　　known——theleastchangeablebyheat。These，consistingseverallyofone
　　atomofeachcomponentelement，arebutonedegreelesshomogeneousthan
　　theelementsthemselves。Moreheterogeneousthanthese，moredecomposable
　　byheat，andthereforelaterintheEarth'shistory，arethedeutoxides，
　　tritoxides，peroxides，etc。;inwhichtwo，three，four，ormoreatomsof
　　oxygenareunitedwithoneatomofmetalorotherbase。Stilllessableto
　　resistheatarethesalts，whichpresentuswithcompoundatomseachmade
　　upoffive，six，seven，eight，ten，twelve，ormoreatoms，ofthreeormore
　　kinds。Thentherearethehydratedsaltsofayetgreaterheterogeneity，
　　whichundergopartialdecompositionatmuchlowertemperatures。Afterthem
　　comethefurther—complicatedsupersaltsanddoublesalts，havingastability
　　againdecreased;andsothroughout。Aftermakingafewunimportantqualifications
　　demandedbypeculiaraffinities，itmaybeassertedasagenerallawofthese
　　inorganiccombinationsthat，otherthingsequal，thestabilitydecreases
　　asthecomplexityincreases。Whenwepasstothecompoundswhichmakeup
　　organicbodes，wefindthisgenerallawfurtherexemplified;wefindmuch
　　greatercomplexityandmuchlessstability。Amoleculeofalbumen，forinstance，
　　consistsofmorethantwohundredultimateunitsoffivedifferentkinds。
　　Accordingtothelatestanalysesitcontainsineachmolecule，72ofcarbon，
　　18ofnitrogen，1ofsulphur，112ofhydrogen，and22ofoxygen——inall，
　　225atoms;or，morestrictlyspeaking，equivalents。Andthissubstanceis
　　sounstableastodecomposeatquitemoderatetemperatures;asthattowhich
　　theoutsideofajointofroastingmeatisexposed。Possiblyitwillbeobjected
　　thatsomeinorganiccompounds，asphosphurettedhydrogen，chlorideofnitrogen，
　　andthenitrogen—explosivesingeneral，aremoredecomposablethanmostorganic
　　compounds。Thisistrue。Buttheadmissionmaybemadewithoutdamageto
　　theargument。Thepropositionisnotthatallsimplecombinationsaremore
　　stablethanallcomplexones。Toestablishourinferenceitisnecessary
　　onlytoshowthat，asanaveragefact，thesimplecombinationscanexist
　　atahighertemperaturethanthecomplexones。Andthisisbeyondquestion。
　　ThusitismanifestthatthepresentchemicalheterogeneityoftheEarth's
　　surface，andofthebodiesuponit，hasarisenbydegreesasthedecrease
　　ofheathaspermitted;andthatithasshownitselfinthreeforms:——first，
　　inthemultiplicationofchemicalcompounds;second，inthegreaternumber
　　ofdifferentelementscontainedinthemoremodernofthesecompounds;and
　　third，inthehigherandmorevariedmultiplesinwhichthesemorenumerouselementscombine。Withoutspecifyingthem，itwillsufficejusttonamethemeteorologic
　　processeseventuallysetupintheEarth'satmosphere，asfurtherillustrating
　　theallegedlaw。Theyequallydisplaythatdestructionofahomogeneousstatewhichresultsfromunequalexposuretoincidentforces。§152。Takeamassofunorganizedbutorganizablematter——either
　　thebodyofoneofthelowestlivingforms，orthegermofoneofthehigher:
　　bothcomparativelyhomogeneous。Consideritscircumstances。Eitheritis
　　immersedinwaterorairoriscontainedwithinaparentorganism。Wherever
　　placed，however，itsouterandinnerpartsstanddifferentlyrelatedtosurrounding
　　agencies——nutriment，oxygen，andthevariousstimuli。Butthisisnotall。
　　Whetheritliesquiescentatthebottomofapoolorontheleafofaplant;
　　whetheritmovesthroughthewaterpreservingsomedefiniteattitude;or
　　whetheritisintheinsideofanadult;itequallyhappensthatcertain
　　partsofitssurfacearemoreexposedtosurroundingagenciesthanother
　　parts——insomecasesmoreexposedtolight，heat，oroxygen，andinother
　　casestothematernaltissuesandtheircontents。Hencemustfollowtheloss
　　ofitsoriginalequilibrium。Thismaytakeplaceinoneoftwoways。Either
　　thedisturbingforcesmaybesuchastoover—balancetheaffinitiesofthe
　　organicelements，andthereresultsdecomposition;or，asordinarilyoccurs，
　　suchchangesareinducedasdonotdestroytheorganiccompoundsbutonly
　　modifythem:thepartsmostexposedtothemodifyingforcesbeingmostmodified。Toelucidatethisafewcasesarerequired。Observefirstwhatappeartobeexceptions。Certainminuteanimalforms
　　presenteithernoappreciabledifferentiationsordifferentiationssoobscure
　　astobemadeoutwithgreatdifficulty。Concerningtheseforms，however，
　　notethefactthatinallcases（somesayinnearlyall）thepresenceof
　　anucleusshowsconformitytothegenerallaw，sinceitimpliesacontrast
　　betweentheinnermostprotoplasmandtheprotoplasmsurroundingit。Butlet
　　uspassontotheseeminglyexceptionalfactthatthesurroundingprotoplasm
　　doesnotexhibitthekindofdifferentiationbetweeninnerandouterabove
　　alleged。Tothisobjection，thereimmediatelypresentsitselftheanswer
　　thatthishomogeneousbody—substancedoesnotbecomeheterogeneousbecause
　　itspartsarenotsubjecttoanypermanentheterogeneityofconditions:it
　　hasnofixedsurface。Inallmembersofthelowestgroup，Proteomyxa，the
　　protoplasmcontinuallyprotrudesitself，nowinthickernowinthinnerprocesses
　　——pseudopodia;provedtohavenolimitingmembranesbyoftencoalescing。
　　These，whentheytouchfragmentsofnutriment，contractanddrawtheminto
　　themassofthebody;sothatwhatwasjustbeforeexternalnowbecomesinternal。
　　Thustherearenofixedrelationsofpartsandthereforenodifferentiations。
　　AnditisnoteworthythatincertainoftheAmoebae，lessexcursivethan
　　othersofthetypeinthemovementsoftheirsubstance，weseeanincipient
　　differentiation:sometimesthereisaninvestingfilm，"delicateand
　　evanescent，"implyingthatanouterpartwhichisforashorttimestationary，
　　beginstobedifferentiated。Perceiving，then，thatthisapparentexception
　　isinfactaverification，wegoontoobservethatpermanentrelationsof
　　innerandouterarefollowedbypermanentdifferentiations。Elsewhere（Essays，
　　i，439）IhavequotedfromSachsvariousproofsthataportionofprotoplasm，
　　whethernormallydetached，asinaspore，orabnormallydetached，asbya
　　rupture，forthwithbecomingglobular，atonceacquiresasurfacedenserthan
　　theinterior;andKernersimilarlydescribestheprotoplasmofazoospore
　　as"fixingitselfandputtingonadelicatecell—wall。"Thesecases，
　　joinedwiththoseofvariousProtozoawhich，ceasingtheiractivechanges
　　ofform，passintoarestingstageandbecomeenclosedinacyst，andjoined
　　withthecasesofProtophyta，likeSphaerellanivalisor"RedSnow，"
　　which，initsyoungstageovoid，flagellate，locomotive，andsecretinga
　　skin，presentlypassesintoarestingstageandbecomessphericalandcovered
　　byasubstantialcell—membrane，yieldclearevidencethatintheselowest
　　typesthereisalapsefromamorehomogeneousstateintoalesshomogeneous
　　state。AndthroughoutthehigherProtozoaandProtophyta，theprimarycontrast
　　isbetweencell—membraneandcell—contents——betweenthepartexposedtoenvironingforcesandthepartshelteredfromthem。Thetransition——themostimportanttransitionwhichtheorganicworld
　　presents——betweenthesimpleformsaboveexemplifiedandthosecompound
　　formsinwhichanumberofsuchareunitedintoacolony，iswellseenin
　　certainminutealgae，PandorinaandEudorina:eachbeingaspherically—arranged
　　colonyofsixteenorthirty—twomembers。Inthisfirstadvancefromunicellular
　　typestomulticellulartypeswefindconformitytothegenerallawinso
　　farthatthehollowsphereconspicuouslydisplaystheprimarycontrastbetween
　　outerandinner;aprimitiveamorphousclusterhasundergoneamarkeddifferentiation
　　ofpartscorrespondingtothedifferenceofconditions。Stillmoreinstructive
　　istheevidencefurnishedbytypesslightlyinadvanceofthese——Pleodorina
　　andVolvox;thefirstconsistingofsome128cellsandthesecondof10，000
　　ormore。Hollowspheresliketheforegoing，theypresentincommonthesignificant
　　traitthat，revolving，astheydo，onaconstantaxisandmovingforward
　　approximatelyinthelineofthataxis，theirtwoendsareexposedtoslightly
　　differentconditions，andtheprimitivehomogeneityofthemembersofthe
　　colonyhas，inconsequence，lapsedintoappropriateheterogeneity。These
　　ciliatedalga—cells，whetherlivingsinglyorjoinedintogroups，severally
　　haveaminuteredspeckwhichisprovedtobesensitivetolight，andcauses
　　motiontowardsit。Nowinthesecompoundformsjustnamed，theeye—spots
　　aremoredevelopedinthosecellsformingtheanteriorpartofthespherical
　　colony—cellswhichalsocarryonmoreactivelythenutritivefunction;while
　　thosecellswhichformtheposteriorpartofthesphere，andcarryonthe
　　reproductivefunction，havesmallereye—spots。Onpassingtotheanimalkingdom
　　（whichatitsrootissolittledifferentiatedfromthevegetalkingdomthat
　　thereareunsettleddisputesrespectingtheinclusionofthelowestforms
　　intheoneortheother）wemeetwithparallelillustrations。Thenucleated
　　cell，whichisthecommonstartingpointforallorganisms，animalandvegetal，
　　presentsusasbeforewiththeprimarycontrastbetweeninnerandouter。