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。