第2章

[footnote]*\"leplusgrandservicequ’onpuisserendrealascienceestd’yfaireplacenetteavantd’yrienconstruire。\"——CUVIER

Theevidenceonwhichsuchconclusionsarebasedisoftwokinds，negativeandpositive。Thevalueofnegativeevidence，inconnectionwiththisinquiry，hasbeensofullyandclearlydiscussedinanaddressfromthechairofthisSociety*，whichnoneofushaveforgotten，thatnothingneedatpresentbesaidaboutit；themore，astheconsiderationswhichhavebeenlaidbeforeyouhavecertainlynottendedtoincreaseyourestimationofsuchevidence。Itwillbepreferabletoturntothepositivefactsofpaleontology，andtoinquirewhattheytellus。

[footnote]*AnniversaryAddressfor1851，’Quart。Journ。

Geol。Soc。’vol。vii。

Weareallaccustomedtospeakofthenumberandtheextentofthechangesinthelivingpopulationoftheglobeduringgeologicaltimeassomethingenormous：andindeedtheyareso，ifweregardonlythenegativedifferenceswhichseparatetheolderrocksfromthemoremodern，andifwelookuponspecificandgenericchangesasgreatchanges，whichfromonepointofview，theytrulyare。Butleavingthenegativedifferencesoutofconsideration，andlookingonlyatthepositivedatafurnishedbythefossilworldfromabroaderpointofview——fromthatofthecomparativeanatomistwhohasmadethestudyofthegreatermodificationsofanimalformhischiefbusiness——asurpriseofanotherkinddawnsuponthemind；andunder’this’aspectthesmallnessofthetotalchangebecomesasastonishingaswasitsgreatnessundertheother。

Therearetwohundredknownordersofplants；ofthesenotoneiscertainlyknowntoexistexclusivelyinthefossilstate。Thewholelapseofgeologicaltimehasasyetyieldednotasinglenewordinaltypeofvegetablestructure。*

[footnote]*SeeHooker’s’IntroductoryEssaytotheFloraofTasmania’，p。xxiii。

Thepositivechangeinpassingfromtherecenttotheancientanimalworldisgreater，butstillsingularlysmall。Nofossilanimalissodistinctfromthosenowlivingastorequiretobearrangedeveninaseparateclassfromthosewhichcontainexistingforms。Itisonlywhenwecometotheorders，whichmayberoughlyestimatedataboutahundredandthirty，thatwemeetwithfossilanimalssodistinctfromthosenowlivingastorequireordersforthemselves；andthesedonotamount，onthemostliberalestimate，tomorethanabout10percent。ofthewhole。

ThereisnocertainlyknownextinctorderofProtozoa；thereisbutoneamongtheCoelenterata——thatoftherugosecorals；thereisnoneamongtheMollusca；therearethree，theCystidea，Blastoidea，andEdrioasterida，amongtheEchinoderms；andtwo，theTrilobitaandEurypterida，amongtheCrustacea；makingaltogetherfiveforthegreatsub—kingdomofAnnulosa。AmongVertebratesthereisnoordinallydistinctfossilfish：thereisonlyoneextinctorderofAmphibia——theLabyrinthodonts；butthereareatleastfourdistinctordersofReptilia，viz。theIchthyosauria，Plesiosauria，Pterosauria，Dinosauria，andperhapsanotherortwo。ThereisnoknownextinctorderofBirds，andnocertainlyknownextinctorderofMammals，theordinaldistinctnessofthe\"Toxodontia\"beingdoubtful。

Theobjectionthatbroadstatementsofthiskind，afterall，restlargelyonnegativeevidenceisobvious，butithaslessforcethanmayatfirstbesupposed；for，asmightbeexpectedfromthecircumstancesofthecase，wepossessmoreabundantpositiveevidenceregardingFishesandmarineMollusksthanrespectinganyotherformsofanimallife；andyettheseofferus，throughthewholerangeofgeologicaltime，nospeciesordinallydistinctfromthosenowliving；whilethefarlessnumerousclassofEchinodermspresentsthree；andtheCrustaceatwo，suchorders，thoughnoneofthesecomedownlaterthanthePaleozoicage。Lastly，theReptiliapresenttheextraordinaryandexceptionalphenomenonofasmanyextinctasexistingorders，ifnotmore；thefourmentionedmaintainingtheirexistencefromtheLiastotheChalkinclusive。

SomeyearsagooneofyourSecretariespointedoutanotherkindofpositivepaleontologicevidencetendingtowardsthesameconclusion——affordedbytheexistenceofwhathetermed\"persistenttypes\"ofvegetableandofanimallife。*Hestated，ontheauthorityofDr。Hooker，thatthereareCarboniferousplantswhichappeartobegenericallyidenticalwithsomenowliving；thattheconeoftheOolitic’Araucaria’ishardlydistinguishablefromthatofanexistingspecies；thatatrue’Pinus’appearsinthePurbecks，anda’Juglans’intheChalk；while，fromtheBagshotSands，a’Banksia’，thewoodofwhichisnotdistinguishablefromthatofspeciesnowlivinginAustralia，hadbeenobtained。

[footnote]*SeetheabstractofaLecture\"OnthePersistentTypesofAnimalLife，\"inthe’NoticesoftheMeetingsoftheRoyalInstitutionofGreatBritain’。——June3，1859，vol。iii。p。151。

Turningtotheanimalkingdom，heaffirmedthetabulatecoralsoftheSilurianrockstobewonderfullylikethosewhichnowexist；whileeventhefamiliesoftheAporosawereallrepresentedintheolderMesozoicrocks。

AmongtheMolluskasimilarfactswereadduced。Letitbeborneinmindthat’Avicula’，’Mytails’，’Chiton’，’Natica’，’Patella’，’Trochus’，’Discina’，’Orbicula’，’Lingula’，’Rhynchonella’，and’Nautilus’，allofwhichareexisting’genera’，aregivenwithoutadoubtasSilurianinthelasteditionof’Siluria’；whilethehighestformsofthehighestCephalopodsarerepresentedintheLiasbyagenus，’Belemnoteuthis’，whichpresentstheclosestrelationtotheexisting’Loligo’。

ThetwohighestgroupsoftheAnnulosa，theInsectaandtheArachnida，arerepresentedintheCoal，eitherbyexistinggenera，orbyformsdifferingfromexistinggenerainquiteminorpeculiarities。

TurningtotheVertebrata，theonlyPaleozoicElasmobranchFishofwhichwehaveanycompleteknowledgeistheDevonianandCarboniferous’Pleuracanthus’，whichdiffersnomorefromexistingSharksthanthesedofromoneanother。

Again，vastasisthenumberofundoubtedlyGanoidfossilFishes，andgreatasistheirrangeintime，alargemassofevidencehasrecentlybeenadducedtoshowthatalmostallthoserespectingwhichwepossesssufficientinformation，arereferabletothesamesub—ordinalgroupsastheexisting’Lepidosteus’，’Polypterus’，andSturgeon；andthatasingularrelationobtainsbetweentheolderandtheyoungerFishes；theformer，theDevonianGanoids，beingalmostallmembersofthesamesub—orderas’Polypterus’，whiletheMesozoicGanoidsarealmostallsimilarlyalliedto’Lepidosteus’。*

[footnote]*\"MemoirsoftheGeologicalSurveyoftheUnitedKingdom。——Decadex。PreliminaryEssayupontheSystematicArrangementoftheFishesoftheDevonianEpoch。\"

Again，whatcanbemoreremarkablethanthesingularconstancyofstructurepreservedthroughoutavastperiodoftimebythefamilyofthePycnodontsandbythatofthetrueCoelacanths；theformerpersisting，withbutinsignificantmodifications，fromtheCarboniferoustotheTertiaryrocks，inclusive；thelatterexisting，withstilllesschange，fromtheCarboniferousrockstotheChalk，inclusive？

AmongReptiles，thehighestlivinggroup，thatoftheCrocodilia，isrepresented，attheearlypartoftheMesozoicepoch，byspeciesidenticalintheessentialcharactersoftheirorganizationwiththosenowliving，anddifferingfromthelatteronlyinsuchmattersastheformofthearticularfacetsofthevertebralcentra，intheextenttowhichthenasalpassagesareseparatedfromthecavityofthemouthbybone，andintheproportionsofthelimbs。

AndevenasregardstheMammalia，thescantyremainsofTriassicandOoliticspeciesaffordnofoundationforthesuppositionthattheorganizationoftheoldestformsdifferednearlysomuchfromsomeofthosewhichnowliveasthesedifferfromoneanother。

Itisneedlesstomultiplytheseinstances；enoughhasbeensaidtojustifythestatementthat，inviewoftheimmensediversityofknownanimalandvegetableforms，andtheenormouslapseoftimeindicatedbytheaccumulationoffossiliferousstrata，theonlycircumstancetobewonderedatis，notthatthechangesoflife，asexhibitedbypositiveevidence，havebeensogreat，butthattheyhavebeensosmall。

Betheygreatorsmall，however，itisdesirabletoattempttoestimatethem。Letus，therefore，takeeachgreatdivisionoftheanimalworldinsuccession，and，wheneveranorderorafamilycanbeshowntohavehadaprolongedexistence，letusendeavourtoascertainhowfarthelatermembersofthegroupdifferfromtheearlierones。Iftheselatermembers，inallorinmanycases，exhibitacertainamountofmodification，thefactis，sofar，evidenceinfavourofagenerallawofchange；and，inaroughway，therapidityofthatchangewillbemeasuredbythedemonstrableamountofmodification。Ontheotherhand，itmustberecollectedthattheabsenceofanymodification，whileitmayleavethedoctrineoftheexistenceofalawofchangewithoutpositivesupport，cannotpossiblydisproveallformsofthatdoctrine，thoughitmayaffordasufficientrefutationofanyofthem。

ThePROTOZOA。——TheProtozoaarerepresentedthroughoutthewholerangeofgeologicalseries，fromtheLowerSilurianformationtothepresentday。ThemostancientformsrecentlymadeknownbyEhrenbergareexceedinglylikethosewhichnowexist：noonehaseverpretendedthatthedifferencebetweenanyancientandanymodernForaminiferaisofmorethangenericvalue，noraretheoldestForaminiferaeithersimpler，moreembryonic，orlessdifferentiated，thantheexistingforms。

TheCOELENTERATA。——TheTabulateCoralshaveexistedfromtheSilurianepochtothepresentday，butIamnotawarethattheancient’Heliolites’possessesasinglemarkofamoreembryonicorlessdifferentiatedcharacter，orlesshighorganization，thantheexisting’Heliopora’。AsfortheAporoseCorals，inwhatrespectistheSilurian’Paleocyclus’lesshighlyorganizedormoreembryonicthanthemodern’Fungia’，ortheLiassicAporosathantheexistingmembersofthesamefamilies？

The’Mollusca’。——Inwhatsenseistheliving’Waldheimia’lessembryonic，ormorespecialized；thanthepaleozoic’Spirifer’；ortheexisting’Rhynchonellae’，’Craniae’，’Discinae’，’Lingulae’，thantheSilurianspeciesofthesamegenera？Inwhatsensecan’Loligo’or’Spirula’besaidtobemorespecialized，orlessembryonic，than’Belemnites’；orthemodernspeciesofLamellibranchandGasteropodgenera，thantheSilurianspeciesofthesamegenera？

TheANNULOSA。——TheCarboniferousInsectaandArachnidaareneitherlessspecialized，normoreembryonic，thanthesethatnowlive，noraretheLiassicCirripediaandMacrura；whileseveraloftheBrachyura，whichappearintheChalk，belongtoexistinggenera；andnoneexhibiteitheranintermediate，oranembryonic，character。

TheVERTEBRARA。——AmongfishesIhavereferredtotheCoelacanthini（comprisingthegenera’Coelacanthus’，’Holophagus’，’Undina’，and’Macropoma’）asaffordinganexampleofapersistenttype；anditismostremarkabletonotethesmallnessofthedifferencesbetweenanyofthesefishes（affectingatmosttheproportionsofthebodyandfins，andthecharacterandsculptureofthescales），notwithstandingtheirenormousrangeintime。Inalltheessentialsofitsverypeculiarstructure，the’Macropoma’oftheChalkisidenticalwiththe’Coelacanthus’oftheCoal。Lookatthegenus’Lepidotus’，again，persistingwithoutamodificationofimportancefromtheLiassictotheEoceneformationsinclusive。

OramongtheTeleostei——inwhatrespectisthe’Beryx’oftheChalkmoreembryonic，orlessdifferentiated，than’Beryxlineatus’ofKingGeorge’sSound？

OrtoturntothehigherVertebrata——inwhatsensearetheLiassicCheloniainferiortothosewhichnowexist？HowaretheCretaceousIchthyosauria，Plesiosauria，orPterosaurialessembryonic，ormoredifferentiated，speciesthanthoseoftheLias？

Orlastly，inwhatcircumstanceisthe’Phascolotherium’moreembryonic，orofamoregeneralizedtype，thanthemodernOpossum；ora’Lophiodon’，ora’Paleotherium’，thanamodern’Tapirus’or’Hyrax’？

Theseexamplesmightbealmostindefinitelymultiplied，butsurelytheyaresufficienttoprovethattheonlysafeandunquestionabletestimonywecanprocure——positiveevidence——failstodemonstrateanysortofprogressivemodificationtowardsalessembryonic，orlessgeneralised，typeinagreatmanygroupsofanimalsoflong—continuedgeologicalexistence。Inthesegroupsthereisabundantevidenceofvariation——noneofwhatisordinarilyunderstoodasprogression；and，iftheknowngeologicalrecordistoberegardedasevenanyconsiderablefragmentofthewhole，itisinconceivablethatanytheoryofanecessarilyprogressivedevelopmentcanstand，forthenumerousordersandfamiliescitedaffordnotraceofsuchaprocess。

Butitisamostremarkablefact，that，whilethegroupswhichhavebeenmentioned，andmanybesides，exhibitnosignofprogressivemodification，thereareothers，co—existingwiththem，underthesameconditions，inwhichmoreorlessdistinctindicationsofsuchaprocessseemstobetraceable。AmongsuchindicationsImayremindyouofthepredominanceofHolostomeGasteropodaintheolderrocksascomparedwiththatofSiphonostomeGasteropodainthelater。Acaselessopentotheobjectionofnegativeevidence，however，isthataffordedbytheTetrabranchiateCephalopoda，theformsoftheshellsandoftheseptalsuturesexhibitingacertainincreaseofcomplexityinthenewergenera。Here，however，oneismetatoncewiththeoccurrenceof’Orthoceras’and’Baculites’atthetwoendsoftheseries，andofthefactthatoneofthesimplestGenera，’Nautilus’，isthatwhichnowexists。

TheCrinoidea，intheabundanceofstalkedformsintheancientformationsascomparedwiththeirpresentrarity，seemtopresentuswithafaircaseofmodificationfromamoreembryonictowardsalessembryoniccondition。Butthen，oncarefulconsiderationofthefacts，theobjectionarisesthatthestalk，calyx，andarmsofthepaleozoicCrinoidareexceedinglydifferentfromthecorrespondingorgansofalarval’Comatula’；anditmightwithperfectjusticebearguedthat’Actinocrinus’and’Eucalyptocrinus’，forexample，departtothefullaswidely，inonedirection，fromthestalkedembryoof’Comatula’，as’Comatula’itselfdoesintheother。

TheEchinidea，again，arefrequentlyquotedasexhibitingagradualpassagefromamoregeneralizedtoamorespecializedtype，seeingthattheelongated，oroval，SpatangoidsappearafterthespheroidalEchinoids。Buthereitmightbeargued，ontheotherhand，thatthespheroidalEchinoids，inreality，departfurtherfromthegeneralplanandfromtheembryonicformthantheelongatedSpatangoidsdo；andthatthepeculiardentalapparatusandthepedicellariaeoftheformeraremarksofatleastasgreatdifferentiationasthepetaloidambulacraandsemitaeofthelatter。

Oncemore，theprevalenceofMacrurousbeforeBrachyurousPodophthalmiais，apparently，afairpieceofevidenceinfavourofprogressivemodificationinthesameorderofCrustacea；andyetthecasewillnotstandmuchsifting，seeingthattheMacrurousPodophthalmiadepartasfarinonedirectionfromthecommontypeofPodophthalmia，orfromanyembryonicconditionoftheBrachyura，astheBrachyuradointheother；

andthatthemiddletermsbetweenMacruraandBrachyura——theAnomura——arelittlebetterrepresentedintheolderMesozoicrocksthantheBrachyuraare。

NoneofthecasesofprogressivemodificationwhicharecitedfromamongtheInvertebrataappeartometohaveafoundationlessopentocriticismthanthese；andifthisbeso，nocarefulreasonerwould，I

think，beinclinedtolayverygreatstressuponthem。AmongtheVertebrata，however，thereareafewexampleswhichappeartobefarlessopentoobjection。

Itis，infact，trueofseveralgroupsofVertebratawhichhavelivedthroughaconsiderablerangeoftime，thattheendoskeleton（moreparticularlythespinalcolumn）oftheoldergenerapresentsalessossified，and，sofar，lessdifferentiated，conditionthanthatoftheyoungergenera。ThustheDevonianGanoids，thoughalmostallmembersofthesamesub—orderas’Polypterus’，andpresentingnumerousimportantresemblancestotheexistinggenus，whichpossessesbiconcavevertebrae，are，forthemostpart，whollydevoidofossifiedvertebralcentra。TheMesozoicLepidosteidae，again，have，atmost，biconcavevertebrae，whiletheexisting’Lepidosteus’hasSalamandroid，opisthocoelous，vertebrae。So，noneofthePaleozoicSharkshaveshownthemselvestobepossessedofossifiedvertebrae，whilethemajorityofmodernSharkspossesssuchvertebrae。Again，themoreancientCrocodiliaandLacertiliahavevertebraewiththearticularfacetsoftheircentraflattenedorbiconcave，whilethemodernmembersofthesamegrouphavethemprocoelous。Butthemostremarkableexamplesofprogressivemodificationofthevertebralcolumn，incorrespondencewithgeologicalage，arethoseaffordedbythePycnodontsamongfish，andtheLabyrinthodontsamongAmphibia。

ThelateableichthyologistHeckelpointedoutthefact，that，whilethePycnodontsneverpossesstruevertebralcentra，theydifferinthedegreeofexpansionandextensionoftheendsofthebonyarchesofthevertebraeuponthesheathofthenotochord；theCarboniferousformsexhibitinghardlyanysuchexpansion，whiletheMesozoicgenerapresentagreaterandgreaterdevelopment，until，intheTertiaryforms，theexpandedendsbecomesuturallyunitedsoastoformasortoffalsevertebra。HermannvonMeyer，again，towhoseluminousresearchesweareindebtedforourpresentlargeknowledgeoftheorganizationoftheolderLabyrinthodonts，hasprovedthattheCarboniferous’Archegosaurus’hadveryimperfectlydevelopedvertebralcentra，whiletheTriassic’Mastodonsaurus’hadthesamepartscompletelyossified。*

[footnote]*AstheAddressispassingthroughthepress（March7，1862），evidenceliesbeforemeoftheexistenceofanewLabyrinthodont（’Pholidogaster’），fromtheEdinburghcoal—field，withwell—ossifiedvertebralcentra。

Theregularityandevennessofthedentitionofthe’Anoplotherium’，ascontrastedwiththatofexistingArtiodactyles，andtheassumednearerapproachofthedentitionofcertainancientCarnivorestothetypicalarrangement，havealsobeencitedasexemplificationsofalawofprogressivedevelopment，butIknowofnoothercasesbasedonpositiveevidencewhichareworthyofparticularnotice。

What，then，doesanimpartialsurveyofthepositivelyascertainedtruthsofpaleontologytestifyinrelationtothecommondoctrinesofprogressivemodification，whichsupposethatmodificationtohavetakenplacebyanecessaryprogressfrommoretolessembryonicforms，orfrommoretolessgeneralizedtypes，withinthelimitsoftheperiodrepresentedbythefossiliferousrocks？

Itnegativesthosedoctrines；foriteithershowsusnoevidenceofanysuchmodification，ordemonstratesittohavebeenveryslight；andastothenatureofthatmodification，ityieldsnoevidencewhatsoeverthattheearliermembersofanylong—continuedgroupweremoregeneralizedinstructurethanthelaterones。Toacertainextent，indeed，itmaybesaidthatimperfectossificationofthevertebralcolumnisanembryoniccharacter；but，ontheotherhand，itwouldbeextremelyincorrecttosupposethatthevertebralcolumnsoftheolderVertebrataareinanysenseembryonicintheirwholestructure。

Obviously，iftheearliestfossiliferousrocksnowknownarecoevalwiththecommencementoflife，andiftheircontentsgiveusanyjustconceptionofthenatureandtheextentoftheearliestfaunaandflora，theinsignificantamountofmodificationwhichcanbedemonstratedtohavetakenplaceinanyonegroupofanimals，orplants，isquiteincompatiblewiththehypothesisthatalllivingformsaretheresultsofanecessaryprocessofprogressivedevelopment，entirelycomprisedwithinthetimerepresentedbythefossiliferousrocks。

Contrariwise，anyadmissiblehypothesisofprogressivemodificationmustbecompatiblewithpersistencewithoutprogression，throughindefiniteperiods。Andshouldsuchanhypothesiseventuallybeprovedtobetrue，intheonlywayinwhichitcanbedemonstrated，viz。byobservationandexperimentupontheexistingformsoflife，theconclusionwillinevitablypresentitself，thatthePaleozoic，Mesozoic，andCainozoicfaunaeandflorae，takentogether，bearsomewhatthesameproportiontothewholeseriesoflivingbeingswhichhaveoccupiedthisglobe，astheexistingfaunaandfloradotothem。

Sucharetheresultsofpaleontologyastheyappear，andhaveforsomeyearsappeared，tothemindofaninquirerwhoregardsthatstudysimplyasoneoftheapplicationsofthegreatbiologicalsciences，andwhodesirestoseeitplaceduponthesamesoundbasisasotherbranchesofphysicalinquiry。Iftheargumentswhichhavebeenbroughtforwardarevalid，probablynoone，inviewofthepresentstateofopinion，willbeinclinedtothinkthetimewastedwhichhasbeenspentupontheirelaboration。