byThomasH。Huxley
　　NATURALHISTORYisthenamefamiliarlyappliedtothestudyofthepropertiesofsuchnaturalbodiesasminerals，plants，andanimals；thescienceswhichembodytheknowledgemanhasacquireduponthesesubjectsarecommonlytermedNaturalSciences，incontradistinctiontootherso—called"physical"sciences；andthosewhodevotethemselvesespeciallytothepursuitofsuchscienceshavebeenandarecommonlytermed"Naturalists。"
　　Linnaeuswasanaturalistinthiswidesense，andhis’SystemaNaturae’
　　wasaworkuponnaturalhistory，inthebroadestacceptationoftheterm；init，thatgreatmethodisingspiritembodiedallthatwasknowninhistimeofthedistinctivecharactersofminerals，animals，andplants。ButtheenormousstimuluswhichLinnaeusgavetotheinvestigationofnaturesoonrendereditimpossiblethatanyonemanshouldwriteanother’SystemaNaturae，’andextremelydifficultforanyonetobecomeevenanaturalistsuchasLinnaeuswas。
　　Greatashavebeentheadvancesmadebyallthethreebranchesofscience，ofoldincludedunderthetitleofnaturalhistory，therecanbenodoubtthatzoologyandbotanyhavegrowninanenormouslygreaterratiothanmineralogy；andhence，asIsuppose，thenameof"naturalhistory"hasgraduallybecomemoreandmoredefinitelyattachedtotheseprominentdivisionsofthesubject，andby"naturalist"peoplehavemeantmoreandmoredistinctlytoimplyastudentofthestructureandfunctionoflivingbeings。
　　Howeverthismaybe，itiscertainthattheadvanceofknowledgehasgraduallywidenedthedistancebetweenmineralogyanditsoldassociates，whileithasdrawnzoologyandbotanyclosertogether；sothatoflateyearsithasbeenfoundconvenient（andindeednecessary）
　　toassociatethescienceswhichdealwithvitalityandallitsphenomenaunderthecommonheadof"biology"；andthebiologistshavecometorepudiateanyblood—relationshipwiththeirfoster—brothers，themineralogists。
　　Certainbroadlawshaveageneralapplicationthroughoutboththeanimalandthevegetableworlds，butthegroundcommontothesekingdomsofnatureisnotofverywideextent，andthemultiplicityofdetailsissogreat，thatthestudentoflivingbeingsfindshimselfobligedtodevotehisattentionexclusivelyeithertotheoneortheother。Ifheelectstostudyplants，underanyaspect，weknowatoncewhattocallhim。Heisabotanist，andhisscienceisbotany。Butiftheinvestigationofanimallifebehischoice，thenamegenerallyappliedtohimwillvaryaccordingtothekindofanimalshestudies，ortheparticularphenomenaofanimallifetowhichheconfineshisattention。Ifthestudyofmanishisobject，heiscalledananatomist，oraphysiologist，oranethnologist；butifhedissectsanimals，orexaminesintothemodeinwhichtheirfunctionsareperformed，heisacomparativeanatomistorcomparativephysiologist。
　　Ifheturnshisattentiontofossilanimals，heisapalaeontologist。
　　Ifhismindismoreparticularlydirectedtothespecificdescription，discrimination，classification，anddistributionofanimals，heistermedazoologist。
　　Forthepurposeofthepresentdiscourse，however，Ishallrecognisenoneofthesetitlessavethelast，whichIshallemployastheequivalentofbotanist，andIshallusethetermzoologyasdenotingthewholedoctrineofanimallife，incontradistinctiontobotany，whichsignifiesthewholedoctrineofvegetablelife。
　　Employedinthissense，zoology，likebotany，isdivisibleintothreegreatbutsubordinatesciences，morphology，physiology，anddistribution，eachofwhichmay，toaverygreatextent，bestudiedindependentlyoftheother。
　　Zoologicalmorphologyisthedoctrineofanimalformorstructure。
　　Anatomyisoneofitsbranches；developmentisanother；whileclassificationistheexpressionoftherelationswhichdifferentanimalsbeartooneanother，inrespectoftheiranatomyandtheirdevelopment。
　　Zoologicaldistributionisthestudyofanimalsinrelationtotheterrestrialconditionswhichobtainnow，orhaveobtainedatanypreviousepochoftheearth’shistory。
　　Zoologicalphysiology，lastly，isthedoctrineofthefunctionsoractionsofanimals。Itregardsanimalbodiesasmachinesimpelledbycertainforces，andperforminganamountofworkwhichcanbeexpressedintermsoftheordinaryforcesofnature。Thefinalobjectofphysiologyistodeducethefactsofmorphology，ontheonehand，andthoseofdistributionontheother，fromthelawsofthemolecularforcesofmatter。
　　Suchisthescopeofzoology。ButifIweretocontentmyselfwiththeenunciationofthesedrydefinitions，Ishouldillexemplifythatmethodofteachingthisbranchofphysicalscience，whichitismychiefbusinessto—nighttorecommend。Letusturnawaythenfromabstractdefinitions。Letustakesomeconcretelivingthing，someanimal，thecommonerthebetter，andletusseehowtheapplicationofcommonsenseandcommonlogictotheobviousfactsitpresents，inevitablyleadsusintoallthesebranchesofzoologicalscience。
　　Ihavebeforemealobster。WhenIexamineit，whatappearstobethemoststrikingcharacteritpresents？Why，Iobservethatthispartwhichwecallthetailofthelobster，ismadeupofsixdistincthardringsandaseventhterminalpiece。IfIseparateoneofthemiddlerings，saythethird，Ifinditcarriesuponitsundersurfaceapairoflimbsorappendages，eachofwhichconsistsofastalkandtwoterminalpieces。SothatIcanrepresentatransversesectionoftheringanditsappendagesuponthediagramboardinthisway。
　　IfInowtakethefourthring，Ifindithasthesamestructure，andsohavethefifthandthesecond；sothat，ineachofthesedivisionsofthetail，Ifindpartswhichcorrespondwithoneanother，aringandtwoappendages；andineachappendageastalkandtwoendpieces。
　　Thesecorrespondingpartsarecalled，inthetechnicallanguageofanatomy，"homologousparts。"Theringofthethirddivisionisthe"homologue"oftheringofthefifth，theappendageoftheformeristhehomologueoftheappendageofthelatter。And，aseachdivisionexhibitscorrespondingpartsincorrespondingplaces，wesaythatallthedivisionsareconstructeduponthesameplan。Butnowletusconsiderthesixthdivision。Itissimilarto，andyetdifferentfrom，theothers。Theringisessentiallythesameasintheotherdivisions；
　　buttheappendageslookatfirstasiftheywereverydifferent；andyetwhenweregardthemclosely，whatdowefind？Astalkandtwoterminaldivisions，exactlyasintheothers，butthestalkisveryshortandverythick，theterminaldivisionsareverybroadandflat，andoneofthemisdividedintotwopieces。
　　Imaysay，therefore，thatthesixthsegmentisliketheothersinplan，butthatitismodifiedinitsdetails。
　　Thefirstsegmentisliketheothers，sofarasitsringisconcerned，andthoughitsappendagesdifferfromanyofthoseyetexaminedinthesimplicityoftheirstructure，partscorrespondingwiththestemandoneofthedivisionsoftheappendagesoftheothersegmentscanbereadilydiscernedinthem。
　　Thusitappearsthatthelobster’stailiscomposedofaseriesofsegmentswhicharefundamentallysimilar，thougheachpresentspeculiarmodificationsoftheplancommontoall。ButwhenIturntotheforepartofthebodyIsee，atfirst，nothingbutagreatshield—likeshell，calledtechnicallythe"carapace，"endinginfrontinasharpspine，oneithersideofwhicharethecuriouscompoundeyes，setupontheendsofstoutmovablestalks。Behindthese，ontheundersideofthebody，aretwopairsoflongfeelers，orantennae，followedbysixpairsofjawsfoldedagainstoneanotheroverthemouth，andfivepairsoflegs，theforemostofthesebeingthegreatpinchers，orclaws，ofthelobster。
　　Itlooks，atfirst，alittlehopelesstoattempttofindinthiscomplexmassaseriesofrings，eachwithitspairofappendages，suchasI
　　haveshownyouintheabdomen，andyetitisnotdifficulttodemonstratetheirexistence。Stripoffthelegs，andyouwillfindthateachpairisattachedtoaverydefinitesegmentoftheunderwallofthebody；butthesesegments，insteadofbeingthelowerpartsoffreerings，asinthetail，aresuchpartsofringswhichareallsolidlyunitedandboundtogether；andthelikeistrueofthejaws，thefeelers，andtheeye—stalks，everypairofwhichisborneuponitsownspecialsegment。Thustheconclusionisgraduallyforceduponus，thatthebodyofthelobsteriscomposedofasmanyringsastherearepairsofappendages，namely，twentyinall，butthatthesixhindmostringsremainfreeandmovable，whilethefourteenfrontringsbecomefirmlysolderedtogether，theirbacksformingonecontinuousshield——thecarapace。
　　Unityofplan，diversityinexecution，isthelessontaughtbythestudyoftheringsofthebody，andthesameinstructionisgivenstillmoreemphaticallybytheappendages。IfIexaminetheoutermostjawIfinditconsistsofthreedistinctportions，aninner，amiddle，andanouter，mounteduponacommonstem；andifIcomparethisjawwiththelegsbehindit，orthejawsinfrontofit，Ifinditquiteeasytosee，that，inthelegs，itisthepartoftheappendagewhichcorrespondswiththeinnerdivision，whichbecomesmodifiedintowhatweknowfamiliarlyasthe"leg，"whilethemiddledivisiondisappears，andtheouterdivisionishiddenunderthecarapace。Norisitmoredifficulttodiscernthat，intheappendagesofthetail，themiddledivisionappearsagainandtheoutervanishes；while，ontheotherhand，intheforemostjaw，theso—calledmandible，theinnerdivisiononlyisleft；and，inthesameway，thepartsofthefeelersandoftheeye—stalkscanbeidentifiedwiththoseofthelegsandjaws。
　　Butwhitherdoesallthistend？Totheveryremarkableconclusionthataunityofplan，ofthesamekindasthatdiscoverableinthetailorabdomenofthelobster，pervadesthewholeorganizationofitsskeleton，sothatIcanreturntothediagramrepresentinganyoneoftheringsofthetail，whichIdrewupontheboard，andbyaddingathirddivisiontoeachappendage，Icanuseitasasortofschemeorplanofanyringofthebody。Icangivenamestoallthepartsofthatfigure，andthenifItakeanysegmentofthebodyofthelobster，Icanpointouttoyouexactly，whatmodificationthegeneralplanhasundergoneinthatparticularsegment；whatparthasremainedmovable，andwhathasbecomefixedtoanother；whathasbeenexcessivelydevelopedandmetamorphosedandwhathasbeensuppressed。
　　ButIimagineIhearthequestion，Howisallthistobetested？Nodoubtitisaprettyandingeniouswayoflookingatthestructureofanyanimal；butisitanythingmore？DoesNatureacknowledge，inanydeeperway，thisunityofplanweseemtotrace？
　　Theobjectionsuggestedbythesequestionsisaveryvalidandimportantone，andmorphologywasinanunsoundstatesolongasitresteduponthemereperceptionoftheanalogieswhichobtainbetweenfullyformedparts。Theuncheckedingenuityofspeculativeanatomistsproveditselffullycompetenttospinanynumberofcontradictoryhypothesesoutofthesamefacts，andendlessmorphologicaldreamsthreatenedtosupplantscientifictheory。
　　Happily，however，thereisacriterionofmorphologicaltruth，andasuretestofallhomologies。Ourlobsterhasnotalwaysbeenwhatweseeit；itwasonceanegg，asemifluidmassofyolk，notsobigasapin’shead，containedinatransparentmembrane，andexhibitingnottheleasttraceofanyoneofthoseorgans，whosemultiplicityandcomplexity，intheadult，aresosurprising。Afteratimeadelicatepatchofcellularmembraneappearedupononefaceofthisyolk，andthatpatchwasthefoundationofthewholecreature，theclayoutofwhichitwouldbemoulded。Graduallyinvestingtheyolk，itbecamesubdividedbytransverseconstrictionsintosegments，theforerunnersoftheringsofthebody。Upontheventralsurfaceofeachoftheringsthussketchedout，apairofbud—likeprominencesmadetheirappearance——therudimentsoftheappendagesofthering。Atfirst，alltheappendageswerealike，but，astheygrew，mostofthembecamedistinguishedintoastemandtwoterminaldivisions，towhichinthemiddlepartofthebody，wasaddedathirdouterdivision；anditwasonlyatalaterperiod，thatbythemodification，orabsorption，ofcertainoftheseprimitiveconstituents，thelimbsacquiredtheirperfectform。
　　Thusthestudyofdevelopmentprovesthatthedoctrineofunityofplanisnotmerelyafancy，thatitisnotmerelyonewayoflookingatthematter，butthatitistheexpressionofdeep—seatednaturalfacts。Thelegsandjawsofthelobstermaynotmerelyberegardedasmodificationsofacommontype，——infactandinnaturetheyareso，——thelegandthejawoftheyounganimalbeing，atfirst，indistinguishable。
　　Thesearewonderfultruths，themoresobecausethezoologistfindsthemtobeofuniversalapplication。Theinvestigationofapolype，ofasnail，ofafish，ofahorse，orofaman，wouldhaveledus，thoughbyalesseasypath，perhaps，toexactlythesamepoint。Unityofplaneverywherelieshiddenunderthemaskofdiversityofstructure——thecomplexiseverywhereevolvedoutofthesimple。Everyanimalhasatfirsttheformofanegg，andeveryanimalandeveryorganicpart，inreachingitsadultstate，passesthroughconditionscommontootheranimalsandotheradultparts；andthisleadsmetoanotherpoint。I
　　havehithertospokenasifthelobsterwerealoneintheworld，but，asIneedhardlyremindyou，therearemyriadsofotheranimalorganisms。
　　Ofthese，some，suchasmen，horses，birds，fishes，snails，slugs，oysters，corals，andsponges，arenotintheleastlikethelobster。
　　Butotheranimals，thoughtheymaydifferagooddealfromthelobster，areyeteitherverylikeit，orarelikesomethingthatislikeit。Thecrayfish，therocklobster，andtheprawn，andtheshrimp，forexample，howeverdifferent，areyetsolikelobsters，thatachildwouldgroupthemasofthelobsterkind，incontradistinctiontosnailsandslugs；andtheselastagainwouldformakindbythemselves，incontradistinctiontocows，horses，andsheep，thecattlekind。
　　Butthisspontaneousgroupinginto"kinds"isthefirstessayofthehumanmindatclassification，orthecallingbyacommonnameofthosethingsthatarealike，andthearrangingtheminsuchamannerasbesttosuggestthesumoftheirlikenessesandunlikenessestootherthings。
　　Thosekindswhichincludenoothersubdivisionsthanthesexes，orvariousbreeds，arecalled，intechnicallanguage，species。TheEnglishlobsterisaspecies，ourcrayfishisanother，ourprawnisanother。Inothercountries，however，therearelobsters，crayfish，andprawns，verylikeours，andyetpresentingsufficientdifferencestodeservedistinction。Naturalists，therefore，expressthisresemblanceandthisdiversitybygroupingthemasdistinctspeciesofthesame"genus。"Butthelobsterandthecrayfish，thoughbelongingtodistinctgenera，havemanyfeaturesincommon，andhencearegroupedtogetherinanassemblagewhichiscalledafamily。Moredistantresemblancesconnectthelobsterwiththeprawnandthecrab，whichareexpressedbyputtingalltheseintothesameorder。Again，moreremote，butstillverydefinite，resemblancesunitethelobsterwiththewoodlouse，thekingcrab，thewaterflea，andthebarnacle，andseparatethemfromallotheranimals；whencetheycollectivelyconstitutethelargergroup，orclass，’Crustacea’。Butthe’Crustacea’exhibitmanypeculiarfeaturesincommonwithinsects，spiders，andcentipedes，sothatthesearegroupedintothestilllargerassemblageor"province"’Articulata’；and，finally，therelationswhichthesehavetowormsandotherloweranimals，areexpressedbycombiningthewholevastaggregateintothesub—kingdomof’Annulosa’。
　　IfIhadworkedmywayfromaspongeinsteadofalobster，Ishouldhavefounditassociated，byliketies，withagreatnumberofotheranimalsintothesub—kingdom’Protozoa’；ifIhadselectedafresh—waterpolypeoracoral，themembersofwhatnaturaliststermthesub—kingdom’Coelenterata’，wouldhavegroupedthemselvesaroundmytype；hadasnailbeenchosen，theinhabitantsofallunivalveandbivalve，landandwater，shells，thelampshells，thesquids，andthesea—matwouldhavegraduallylinkedthemselvesontoitasmembersofthesamesub—kingdomof’Mollusca’；andfinally，startingfromman，Ishouldhavebeencompelledtoadmitfirst，theape，therat，thehorse，thedog，intothesameclass；andthenthebird，thecrocodile，theturtle，thefrog，andthefish，intothesamesub—kingdomof’Vertebrata’。
　　AndifIhadfollowedoutallthesevariouslinesofclassificationfully，Ishoulddiscoverintheendthattherewasnoanimal，eitherrecentorfossil，whichdidnotatoncefallintooneorotherofthesesub—kingdoms。Inotherwords，everyanimalisorganizedupononeorotherofthefive，ormore，plans，whoseexistencerendersourclassificationpossible。Andsodefinitelyandpreciselymarkedisthestructureofeachanimal，that，inthepresentstateofourknowledge，thereisnottheleastevidencetoprovethataform，intheslightestdegreetransitionalbetweenanyofthetwogroups’Vertebrata’，’Annulosa’，’Mollusca’，and’Coelenterata’，eitherexists，orhasexisted，duringthatperiodoftheearth’shistorywhichisrecordedbythegeologist。Nevertheless，youmustnotforamomentsuppose，becausenosuchtransitionalformsareknown，thatthemembersofthesub—kingdomsaredisconnectedfrom，orindependentof，oneanother。Onthecontrary，intheirearliestconditiontheyareallalike，andtheprimordialgermsofaman，adog，abird，afish，abeetle，asnail，andapolypeare，innoessentialstructuralrespects，distinguishable。
　　Inthisbroadsense，itmaywithtruthbesaid，thatalllivinganimals，andallthosedeadcreationswhichgeologyreveals，areboundtogetherbyanall—pervadingunityoforganization，ofthesamecharacter，thoughnotequalindegree，tothatwhichenablesustodiscernoneandthesameplanamidstthetwentydifferentsegmentsofalobster’sbody。
　　Trulyithasbeensaid，thattoacleareyethesmallestfactisawindowthroughwhichtheInfinitemaybeseen。
　　Turningfromthesepurelymorphologicalconsiderations，letusnowexamineintothemannerinwhichtheattentivestudyofthelobsterimpelsusintootherlinesofresearch。
　　LobstersarefoundinalltheEuropeanseas；butontheoppositeshoresoftheAtlanticandintheseasofthesouthernhemispheretheydonotexist。Theyare，however，representedintheseregionsbyverycloselyallied，butdistinctforms——the’HomarusAmericanus’andthe’HomarusCapensis’:sothatwemaysaythattheEuropeanhasonespeciesof’Homarus’；theAmerican，another；theAfrican，another；andthustheremarkablefactsofgeographicaldistributionbegintodawnuponus。
　　Again，ifweexaminethecontentsoftheearth’scrust，weshallfindinthelatterofthosedeposits，whichhaveservedasthegreatburyinggroundsofpastages，numberlesslobster—likeanimals，butnonesosimilartoourlivinglobsterastomakezoologistssurethattheybelongedeventothesamegenus。Ifwegostillfurtherbackintime，wediscover，intheoldestrocksofall，theremainsofanimals，constructedonthesamegeneralplanasthelobster，andbelongingtothesamegreatgroupof’Crustacea’；butforthemostparttotallydifferentfromthelobster，andindeedfromanyotherlivingformofcrustacean；andthuswegainanotionofthatsuccessivechangeoftheanimalpopulationoftheglobe，inpastages，whichisthemoststrikingfactrevealedbygeology。
　　Consider，now，whereourinquirieshaveledus。Westudiedourtypemorphologically，whenwedetermineditsanatomyanditsdevelopment，andwhencomparingit，intheserespects，withotheranimals，wemadeoutitsplaceinasystemofclassification。Ifweweretoexamineeveryanimalinasimilarmanner，weshouldestablishacompletebodyofzoologicalmorphology。
　　Again，weinvestigatedthedistributionofourtypeinspaceandintime，and，ifthelikehadbeendonewitheveryanimal，thesciencesofgeographicalandgeologicaldistributionwouldhaveattainedtheirlimit。
　　Butyouwillobserveoneremarkablecircumstance，that，uptothispoint，thequestionofthelifeoftheseorganismshasnotcomeunderconsideration。Morphologyanddistributionmightbestudiedalmostaswell，ifanimalsandplantswereapeculiarkindofcrystals，andpossessednoneofthosefunctionswhichdistinguishlivingbeingssoremarkably。Butthefactsofmorphologyanddistributionhavetobeaccountedfor，andthescience，whoseaimitistoaccountforthem，isPhysiology。
　　Letusreturntoourlobsteroncemore。Ifwewatchedthecreatureinitsnativeelement，weshouldseeitclimbingactivelythesubmergedrocks，amongwhichitdelightstolive，bymeansofitsstronglegs；orswimmingbypowerfulstrokesofitsgreattail，theappendagesofwhosesixthjointarespreadoutintoabroadfan—likepropeller:seizeit，anditwillshowyouthatitsgreatclawsarenomeanweaponsofoffence；suspendapieceofcarrionamongitshaunts，anditwillgreedilydevourit，tearingandcrushingthefleshbymeansofitsmultitudinousjaws。
　　Supposethatwehadknownnothingofthelobsterbutasaninertmass，anorganiccrystal，ifImayusethephrase，andthatwecouldsuddenlyseeitexertingallthesepowers，whatwonderfulnewideasandnewquestionswouldariseinourminds！Thegreatnewquestionwouldbe，"Howdoesallthistakeplace？"thechiefnewideawouldbe，theideaofadaptationtopurpose，——thenotion，thattheconstituentsofanimalbodiesarenotmereunconnectedparts，butorgansworkingtogethertoanend。Letusconsiderthetailofthelobsteragainfromthispointofview。Morphologyhastaughtusthatitisaseriesofsegmentscomposedofhomologousparts，whichundergovariousmodifications——beneathandthroughwhichacommonplanofformationisdiscernible。ButifIlookatthesamepartphysiologically，Iseethatitisamostbeautifullyconstructedorganoflocomotion，bymeansofwhichtheanimalcanswiftlypropelitselfeitherbackwardsorforwards。
　　Buthowisthisremarkablepropulsivemachinemadetoperformitsfunctions？IfIweresuddenlytokilloneoftheseanimalsandtotakeoutallthesoftparts，Ishouldfindtheshelltobeperfectlyinert，tohavenomorepowerofmovingitselfthanispossessedbythemachineryofamillwhendisconnectedfromitssteam—engineorwater—wheel。ButifIweretoopenit，andtakeoutthevisceraonly，leavingthewhiteflesh，Ishouldperceivethatthelobstercouldbendandextenditstailaswellasbefore。IfIweretocutoffthetail，I
　　shouldceasetofindanyspontaneousmotioninit；butonpinchinganyportionoftheflesh，Ishouldobservethatitunderwentaverycuriouschange——eachfibrebecomingshorterandthicker。Bythisactofcontraction，asitistermed，thepartstowhichtheendsofthefibreareattachedare，ofcourse，approximated；andaccordingtotherelationsoftheirpointsofattachmenttothecentresofmotionsofthedifferentrings，thebendingortheextensionofthetailresults。
　　Closeobservationofthenewly—openedlobsterwouldsoonshowthatallitsmovementsareduetothesamecause——theshorteningandthickeningofthesefleshyfibres，whicharetechnicallycalledmuscles。
　　Here，then，isacapitalfact。Themovementsofthelobsterareduetomuscularcontractility。Butwhydoesamusclecontractatonetimeandnotatanother？Whydoesonewholegroupofmusclescontractwhenthelobsterwishestoextendhistail，andanothergroupwhenhedesirestobendit？Whatisitoriginates，directs，andcontrolsthemotivepower？
　　Experiment，thegreatinstrumentfortheascertainmentoftruthinphysicalscience，answersthisquestionforus。Intheheadofthelobsterthereliesasmallmassofthatpeculiartissuewhichisknownasnervoussubstance。Cordsofsimilarmatterconnectthisbrainofthelobster，directlyorindirectly，withthemuscles。Now，ifthesecommunicatingcordsarecut，thebrainremainingentire，thepowerofexertingwhatwecallvoluntarymotioninthepartsbelowthesectionisdestroyed；andontheotherhand，if，thecordsremainingentire，thebrainmassbedestroyed，thesamevoluntarymobilityisequallylost。
　　Whencetheinevitableconclusionis，thatthepoweroforiginatingthesemotionsresidesinthebrain，andispropagatedalongthenervouscords。
　　Inthehigheranimalsthephenomenawhichattendthistransmissionhavebeeninvestigated，andtheexertionofthepeculiarenergywhichresidesinthenerveshasbeenfoundtobeaccompaniedbyadisturbanceoftheelectricalstateoftheirmolecules。
　　Ifwecouldexactlyestimatethesignificationofthisdisturbance；ifwecouldobtainthevalueofagivenexertionofnerveforcebydeterminingthequantityofelectricity，orofheat，ofwhichitistheequivalent；ifwecouldascertainuponwhatarrangement，orotherconditionofthemoleculesofmatter，themanifestationofthenervousandmuscularenergiesdepends（anddoubtlesssciencewillsomedayorotherascertainthesepoints），physiologistswouldhaveattainedtheirultimategoalinthisdirection；theywouldhavedeterminedtherelationofthemotiveforceofanimalstotheotherformsofforcefoundinnature；andifthesameprocesshadbeensuccessfullyperformedforalltheoperationswhicharecarriedonin，andby，theanimalframe，physiologywouldbeperfect，andthefactsofmorphologyanddistributionwouldbededuciblefromthelawswhichphysiologistshadestablished，combinedwiththosedeterminingtheconditionofthesurroundinguniverse。
　　ThereisnotafragmentoftheorganismofthishumbleanimalwhosestudywouldnotleadusintoregionsofthoughtaslargeasthosewhichIhavebrieflyopeneduptoyou；butwhatIhavebeensaying，Itrust，hasnotonlyenabledyoutoformaconceptionofthescopeandpurportofzoology，buthasgivenyouanimperfectexampleofthemannerinwhich，inmyopinion，thatscience，orindeedanyphysicalscience，maybebesttaught。Thegreatmatteris，tomaketeachingrealandpractical，byfixingtheattentionofthestudentonparticularfacts；
　　butatthesametimeitshouldberenderedbroadandcomprehensive，byconstantreferencetothegeneralizationsofwhichallparticularfactsareillustrations。Thelobsterhasservedasatypeofthewholeanimalkingdom，anditsanatomyandphysiologyhaveillustratedforussomeofthegreatesttruthsofbiology。ThestudentwhohasonceseenforhimselfthefactswhichIhavedescribed，hashadtheirrelationsexplainedtohim，andhasclearlycomprehendedthem，has，sofar，aknowledgeofzoology，whichisrealandgenuine，howeverlimiteditmaybe，andwhichisworthmorethanallthemerereadingknowledgeofthesciencehecouldeveracquire。Hiszoologicalinformationis，sofar，knowledgeandnotmerehear—say。
　　Andifitweremybusinesstofityouforthecertificateinzoologicalsciencegrantedbythisdepartment，IshouldpursueacoursepreciselysimilarinprincipletothatwhichIhavetakento—night。Ishouldselectafresh—watersponge，afresh—waterpolypeora’Cyanaea’，afresh—watermussel，alobster，afowl，astypesofthefiveprimarydivisionsoftheanimalkingdom。Ishouldexplaintheirstructureveryfully，andshowhoweachillustratedthegreatprinciplesofzoology。
　　Havinggoneverycarefullyandfullyoverthisground，Ishouldfeelthatyouhadasafefoundation，andIshouldthentakeyouinthesameway，butlessminutely，oversimilarlyselectedillustrativetypesoftheclasses；andthenIshoulddirectyourattentiontothespecialformsenumeratedundertheheadoftypes，inthissyllabus，andtotheotherfactstherementioned。
　　Thatwould，speakinggenerally，bemyplan。ButIhaveundertakentoexplaintoyouthebestmodeofacquiringandcommunicatingaknowledgeofzoology，andyoumaythereforefairlyaskmeforamoredetailedandpreciseaccountofthemannerinwhichIshouldproposetofurnishyouwiththeinformationIreferto。
　　Myownimpressionis，thatthebestmodelforallkindsoftraininginphysicalscienceisthataffordedbythemethodofteachinganatomy，inuseinthemedicalschools。Thismethodconsistsofthreeelements——lectures，demonstrations，andexaminations。
　　Theobjectoflecturesis，inthefirstplace，toawakentheattentionandexcitetheenthusiasmofthestudent；andthis，Iamsure，maybeeffectedtoafargreaterextentbytheoraldiscourseandbythepersonalinfluenceofarespectedteacherthaninanyotherway。
　　Secondly，lectureshavethedoubleuseofguidingthestudenttothesalientpointsofasubject，andatthesametimeforcinghimtoattendtothewholeofit，andnotmerelytothatpartwhichtakeshisfancy。
　　Andlastly，lecturesaffordthestudenttheopportunityofseekingexplanationsofthosedifficultieswhichwill，andindeedoughtto，ariseinthecourseofhisstudies。
　　Butforastudenttoderivetheutmostpossiblevaluefromlectures，severalprecautionsareneedful。
　　Ihaveastrongimpressionthatthebetteradiscourseis，asanoration，theworseitisasalecture。Theflowofthediscoursecarriesyouonwithoutproperattentiontoitssense；youdropawordoraphrase，youlosetheexactmeaningforamoment，andwhileyoustrivetorecoveryourself，thespeakerhaspassedontosomethingelse。
　　ThepracticeIhaveadoptedoflateyears，inlecturingtostudents，istocondensethesubstanceofthehour’sdiscourseintoafewdrypropositions，whicharereadslowlyandtakendownfromdictation；thereadingofeachbeingfollowedbyafreecommentaryexpandingandillustratingtheproposition，explainingterms，andremovinganydifficultiesthatmaybeattackableinthatway，bydiagramsmaderoughly，andseentogrowunderthelecturer’shand。Inthismanneryou，atanyrate，insuretheco—operationofthestudenttoacertainextent。Hecannotleavethelecture—roomentirelyemptyifthetakingofnotesisenforced；andastudentmustbepreternaturallydullandmechanical，ifhecantakenotesandhearthemproperlyexplained，andyetlearnnothing。
　　WhatbooksshallIread？isaquestionconstantlyputbythestudenttotheteacher。Myreplyusuallyis，"None:writeyournotesoutcarefullyandfully；strivetounderstandthemthoroughly；cometomefortheexplanationofanythingyoucannotunderstand；andIwouldratheryoudidnotdistractyourmindbyreading。"Aproperlycomposedcourseoflecturesoughttocontainfullyasmuchmatterasastudentcanassimilateinthetimeoccupiedbyitsdelivery；andtheteachershouldalwaysrecollectthathisbusinessistofeed，andnottocramtheintellect。Indeed，Ibelievethatastudentwhogainsfromacourseoflecturesthesimplehabitofconcentratinghisattentionuponadefinitelylimitedseriesoffacts，untiltheyarethoroughlymastered，hasmadeastepofimmeasurableimportance。
　　But，howevergoodlecturesmaybe，andhoweverextensivethecourseofreadingbywhichtheyarefollowedup，theyarebutaccessoriestothegreatinstrumentofscientificteaching——demonstration。IfIinsistunweariedly，nayfanatically，upontheimportanceofphysicalscienceasaneducationalagent，itisbecausethestudyofanybranchofscience，ifproperlyconducted，appearstometofillupavoidleftbyallothermeansofeducation。Ihavethegreatestrespectandloveforliterature；nothingwouldgrievememorethantoseeliterarytrainingotherthanaveryprominentbranchofeducation:indeed，Iwishthatrealliterarydisciplinewerefarmoreattendedtothanitis；butI
　　cannotshutmyeyestothefact，thatthereisavastdifferencebetweenmenwhohavehadapurelyliterary，andthosewhohavehadasoundscientific，training。
　　Seekingforthecauseofthisdifference，IimagineIcanfinditinthefactthat，intheworldofletters，learningandknowledgeareone，andbooksarethesourceofboth；whereasinscience，asinlife，learningandknowledgearedistinct，andthestudyofthings，andnotofbooks，isthesourceofthelatter。
　　Allthatliteraturehastobestowmaybeobtainedbyreadingandbypracticalexerciseinwritingandinspeaking；butIdonotexaggeratewhenIsay，thatnoneofthebestgiftsofsciencearetobewonbythesemeans。Onthecontrary，thegreatbenefitwhichascientificeducationbestows，whetherastrainingorasknowledge，isdependentupontheextenttowhichthemindofthestudentisbroughtintoimmediatecontactwithfacts——uponthedegreetowhichhelearnsthehabitofappealingdirectlytoNature，andofacquiringthroughhissensesconcreteimagesofthosepropertiesofthings，whichare，andalwayswillbe，butapproximativelyexpressedinhumanlanguage。OurwayoflookingatNature，andofspeakingabouther，variesfromyeartoyear；butafactonceseen，arelationofcauseandeffect，oncedemonstrativelyapprehended，arepossessionswhichneitherchangenorpassaway，but，onthecontrary，formfixedcentres，aboutwhichothertruthsaggregatebynaturalaffinity。
　　Therefore，thegreatbusinessofthescientificteacheris，toimprintthefundamental，irrefragablefactsofhisscience，notonlybywordsuponthemind，butbysensibleimpressionsupontheeye，andear，andtouchofthestudent，insocompleteamanner，thateverytermused，orlawenunciated，shouldafterwardscallupvividimagesoftheparticularstructural，orother，factswhichfurnishedthedemonstrationofthelaw，ortheillustrationoftheterm。
　　Nowthisimportantoperationcanonlybeachievedbyconstantdemonstration，whichmaytakeplacetoacertainimperfectextentduringalecture，butwhichoughtalsotobecarriedonindependently，andwhichshouldbeaddressedtoeachindividualstudent，theteacherendeavouring，notsomuchtoshowathingtothelearner，astomakehimseeitforhimself。
　　Iamwellawarethattherearegreatpracticaldifficultiesinthewayofeffectualzoologicaldemonstrations。Thedissectionofanimalsisnotaltogetherpleasant，andrequiresmuchtime；norisiteasytosecureanadequatesupplyoftheneedfulspecimens。Thebotanisthashereagreatadvantage；hisspecimensareeasilyobtained，arecleanandwholesome，andcanbedissectedinaprivatehouseaswellasanywhereelse；andhence，Ibelieve，thefact，thatbotanyissomuchmorereadilyandbettertaughtthanitssisterscience。But，beitdifficultorbeiteasy，ifzoologicalscienceistobeproperlystudied，demonstration，and，consequently，dissection，mustbehad。
　　Withoutit，nomancanhaveareallysoundknowledgeofanimalorganization。
　　Agooddealmaybedone，however，withoutactualdissectiononthestudent’spart，bydemonstrationuponspecimensandpreparations；andinallprobabilityitwouldnotbeverydifficult，werethedemandsufficient，toorganizecollectionsofsuchobjects，sufficientforallthepurposesofelementaryteaching，atacomparativelycheaprate。
　　Evenwithoutthese，muchmightbeeffected，ifthezoologicalcollections，whichareopentothepublic，werearrangedaccordingtowhathasbeentermedthe"typicalprinciple"；thatistosay，ifthespecimensexposedtopublicviewweresoselectedthatthepubliccouldlearnsomethingfromthem，insteadofbeing，asatpresent，merelyconfusedbytheirmultiplicity。Forexample，thegrandornithologicalgalleryattheBritishMuseumcontainsbetweentwoandthreethousandspeciesofbirds，andsometimesfiveorsixspecimensofaspecies。
　　Theyareveryprettytolookat，andsomeofthecasesare，indeed，splendid；butIwillundertaketosay，thatnomanbutaprofessedornithologisthasevergatheredmuchinformationfromthecollection。
　　Certainly，nooneofthetensofthousandsofthegeneralpublicwhohavewalkedthroughthatgalleryeverknewmoreabouttheessentialpeculiaritiesofbirdswhenheleftthegallerythanwhenheenteredit。Butif，somewhereinthatvasthall，therewereafewpreparations，exemplifyingtheleadingstructuralpeculiaritiesandthemodeofdevelopmentofacommonfowl；ifthetypesofthegenera，theleadingmodificationsintheskeleton，intheplumageatvariousages，inthemodeofnidification，andthelike，amongbirds，weredisplayed；andiftheotherspecimenswereputawayinaplacewherethemenofscience，towhomtheyarealoneuseful，couldhavefreeaccesstothem，Icanconceivethatthiscollectionmightbecomeagreatinstrumentofscientificeducation。
　　ThelastimplementoftheteachertowhichIhaveadvertedisexamination——ameansofeducationnowsothoroughlyunderstoodthatI
　　needhardlyenlargeuponit。Iholdthatbothwrittenandoralexaminationsareindispensable，and，byrequiringthedescriptionofspecimens，theymaybemadetosupplementdemonstration。
　　Suchisthefullestreplythetimeatmydisposalwillallowmetogivetothequestion——howmayaknowledgeofzoologybebestacquiredandcommunicated？
　　Butthereisapreviousquestionwhichmaybemoved，andwhich，infact，Iknowmanyareinclinedtomove。Itisthequestion，whyshouldtrainingmastersbeencouragedtoacquireaknowledgeofthis，oranyotherbranchofphysicalscience？Whatistheuse，itissaid，ofattemptingtomakephysicalscienceabranchofprimaryeducation？Isitnotprobablethatteachers，inpursuingsuchstudies，willbeledastrayfromtheacquirementofmoreimportantbutlessattractiveknowledge？And，eveniftheycanlearnsomethingofsciencewithoutprejudicetotheirusefulness，whatisthegoodoftheirattemptingtoinstilthatknowledgeintoboyswhoserealbusinessistheacquisitionofreading，writing，andarithmetic？
　　Thesequestionsare，andwillbe，verycommonlyasked，fortheyarisefromthatprofoundignoranceofthevalueandtruepositionofphysicalscience，whichinfeststhemindsofthemosthighlyeducatedandintelligentclassesofthecommunity。ButifIdidnotfeelwellassuredthattheyarecapableofbeingeasilyandsatisfactorilyanswered；thattheyhavebeenansweredoverandoveragain；andthatthetimewillcomewhenmenofliberaleducationwillblushtoraisesuchquestions，——Ishouldbeashamedofmypositionhereto—night。
　　Withoutdoubt，itisyourgreatandveryimportantfunctiontocarryoutelementaryeducation；withoutquestion，anythingthatshouldinterferewiththefaithfulfulfilmentofthatdutyonyourpartwouldbeagreatevil；andifIthoughtthatyouracquirementoftheelementsofphysicalscience，andyourcommunicationofthoseelementstoyourpupils，involvedanysortofinterferencewithyourproperduties，I
　　shouldbethefirstpersontoprotestagainstyourbeingencouragedtodoanythingofthekind。
　　Butisittruethattheacquisitionofsuchaknowledgeofscienceasisproposed，andthecommunicationofthatknowledge，arecalculatedtoweakenyourusefulness？OrmayInotratherask，isitpossibleforyoutodischargeyourfunctionsproperlywithouttheseaids？
　　Whatisthepurposeofprimaryintellectualeducation？Iapprehendthatitsfirstobjectistotraintheyoungintheuseofthosetoolswherewithmenextractknowledgefromtheever—shiftingsuccessionofphenomenawhichpassbeforetheireyes；andthatitssecondobjectistoinformthemofthefundamentallawswhichhavebeenfoundbyexperiencetogovernthecourseofthings，sothattheymaynotbeturnedoutintotheworldnaked，defenceless，andapreytotheeventstheymightcontrol。
　　Aboyistaughttoreadhisownandotherlanguages，inorderthathemayhaveaccesstoinfinitelywiderstoresofknowledgethancouldeverbeopenedtohimbyoralintercoursewithhisfellowmen；helearnstowrite，thathismeansofcommunicationwiththerestofmankindmaybeindefinitelyenlarged，andthathemayrecordandstoreuptheknowledgeheacquires。Heistaughtelementarymathematics，thathemayunderstandallthoserelationsofnumberandform，uponwhichthetransactionsofmen，associatedincomplicatedsocieties，arebuilt，andthathemayhavesomepracticeindeductivereasoning。
　　Alltheseoperationsofreading，writing，andciphering，areintellectualtools，whoseuseshould，beforeallthings，belearned，andlearnedthoroughly；sothattheyouthmaybeenabledtomakehislifethatwhichitoughttobe，acontinualprogressinlearningandinwisdom。
　　But，inaddition，primaryeducationendeavourstofitaboyoutwithacertainequipmentofpositiveknowledge。Heistaughtthegreatlawsofmorality；thereligionofhissect；somuchhistoryandgeographyaswilltellhimwherethegreatcountriesoftheworldare，whattheyare，andhowtheyhavebecomewhattheyare。
　　Withoutdoubtallthesearemostfittingandexcellentthingstoteachaboy；Ishouldbeverysorrytoomitanyofthemfromanyschemeofprimaryintellectualeducation。Thesystemisexcellent，sofarasitgoes。
　　ButifIregarditclosely，acuriousreflectionarises。Isupposethat，fifteenhundredyearsago，thechildofanywell—to—doRomancitizenwastaughtjustthesesamethings；readingandwritinginhisown，and，perhaps，theGreektongue；theelementsofmathematics；andthereligion，morality，history，andgeographycurrentinhistime。
　　Furthermore，IdonotthinkIerrinaffirming，that，ifsuchaChristianRomanboy，whohadfinishedhiseducation，couldbetransplantedintooneofourpublicschools，andpassthroughitscourseofinstruction，hewouldnotmeetwithasingleunfamiliarlineofthought；amidstallthenewfactshewouldhavetolearn，notonewouldsuggestadifferentmodeofregardingtheuniversefromthatcurrentinhisowntime。
　　Andyetsurelythereissomegreatdifferencebetweenthecivilizationofthefourthcenturyandthatofthenineteenth，andstillmorebetweentheintellectualhabitsandtoneofthoughtofthatdayandthis？
　　Andwhathasmadethisdifference？Ianswerfearlessly——Theprodigiousdevelopmentofphysicalsciencewithinthelasttwocenturies。
　　Moderncivilizationrestsuponphysicalscience；takeawayhergiftstoourowncountry，andourpositionamongtheleadingnationsoftheworldisgoneto—morrow；foritisphysicalscienceonly，thatmakesintelligenceandmoralenergystrongerthanbruteforce。
　　Thewholeofmodernthoughtissteepedinscience；ithasmadeitswayintotheworksofourbestpoets，andeventhemeremanofletters，whoaffectstoignoreanddespisescience，isunconsciouslyimpregnatedwithherspirit，andindebtedforhisbestproductstohermethods。I
　　believethatthegreatestintellectualrevolutionmankindhasyetseenisnowslowlytakingplacebyheragency。Sheisteachingtheworldthattheultimatecourtofappealisobservationandexperiment，andnotauthority；sheisteachingittoestimatethevalueofevidence；sheiscreatingafirmandlivingfaithintheexistenceofimmutablemoralandphysicallaws，perfectobediencetowhichisthehighestpossibleaimofanintelligentbeing。
　　Butofallthisyouroldstereotypedsystemofeducationtakesnonote。
　　Physicalscience，itsmethods，itsproblems，anditsdifficulties，willmeetthepoorestboyateveryturn，andyetweeducatehiminsuchamannerthatheshallentertheworldasignorantoftheexistenceofthemethodsandfactsofscienceasthedayhewasborn。Themodernworldisfullofartillery；andweturnoutourchildrentodobattleinit，equippedwiththeshieldandswordofanancientgladiator。
　　Posteritywillcryshameonusifwedonotremedythisdeplorablestateofthings。Nay，ifwelivetwentyyearslonger，ourownconscienceswillcryshameonus。
　　Itismyfirmconvictionthattheonlywaytoremedyitis，tomaketheelementsofphysicalscienceanintegralpartofprimaryeducation。I
　　haveendeavouredtoshowyouhowthatmaybedoneforthatbranchofsciencewhichitismybusinesstopursue；andIcanbutadd，thatI
　　shouldlookuponthedaywheneveryschoolmasterthroughoutthislandwasacentreofgenuine，howeverrudimentary，scientificknowledge，asanepochinthehistoryofthecountry。
　　Butletmeentreatyoutoremembermylastwords。Addressingmyselftoyou，asteachers，Iwouldsay，merebooklearninginphysicalscienceisashamandadelusion——whatyouteach，unlessyouwishtobeimpostors，thatyoumustfirstknow；andrealknowledgeinsciencemeanspersonalacquaintancewiththefacts，betheyfewormany。*
　　[footnote]*Ithasbeensuggestedtomethatthesewordsmaybetakentoimplyadiscouragementonmypartofanysortofscientificinstructionwhichdoesnotgiveanacquaintancewiththefactsatfirsthand。Butthisisnotmymeaning。Theidealofscientificteachingis，nodoubt，asystembywhichthescholarseeseveryfactforhimself，andtheteachersuppliesonlytheexplanations。
　　Circumstances，however，donotoftenallowoftheattainmentofthatideal，andwemustputupwiththenextbestsystem——oneinwhichthescholartakesagooddealontrustfromateacher，who，knowingthefactsbyhisownknowledge，candescribethemwithsomuchvividnessastoenablehisaudiencetoformcompetentideasconcerningthem。ThesystemwhichIrepudiateisthatwhichallowsteacherswhohavenotcomeintodirectcontactwiththeleadingfactsofasciencetopasstheirsecond—handinformationon。Thescientificvirus，likevaccinelymph，ifpassedthroughtoolongasuccessionoforganisms，willloseallitseffectinprotectingtheyoungagainsttheintellectualepidemicstowhichtheyareexposed。