第6章

类别:其他 作者:Charles Darwin字数:5244更新时间:18/12/21 17:23:57
butitisnotpossibletogiveanadequateideaofthehigherfeelingsofwonder,astonishment,anddevotion,whichfillandelevatethemind。 April19th——LeavingSocego,duringthetwofirstdays,weretracedoursteps。Itwasverywearisomework,astheroadgenerallyranacrossaglaringhotsandyplain,notfarfromthecoast。Inoticedthateachtimethehorseputitsfootonthefinesiliceoussand,agentlechirpingnoisewasproduced。Onthethirddaywetookadifferentline,andpassedthroughthegaylittlevillageofMadredeDeos。ThisisoneoftheprincipallinesofroadinBrazil;yetitwasinsobadastatethatnowheeledvehicle,exceptingtheclumsybullock-wagon,couldpassalong。Inourwholejourneywedidnotcrossasinglebridgebuiltofstone;andthosemadeoflogsofwoodwerefrequentlysomuchoutofrepair,thatitwasnecessarytogoononesidetoavoidthem。Alldistancesareinaccuratelyknown。Theroadisoftenmarkedbycrosses,intheplaceofmilestones,tosignifywherehumanbloodhasbeenspilled。Ontheeveningofthe23rdwearrivedatRio,havingfinishedourpleasantlittleexcursion。 DuringtheremainderofmystayatRio,IresidedinacottageatBotofogoBay。Itwasimpossibletowishforanythingmoredelightfulthanthustospendsomeweeksinsomagnificentacountry。InEnglandanypersonfondofnaturalhistoryenjoysinhiswalksagreatadvantage,byalwayshavingsomethingtoattracthisattention;butinthesefertileclimates,teemingwithlife,theattractionsaresonumerous,thatheisscarcelyabletowalkatall。 ThefewobservationswhichIwasenabledtomakewerealmostexclusivelyconfinedtotheinvertebrateanimals。TheexistenceofadivisionofthegenusPlanaria,whichinhabitsthedryland,interestedmemuch。Theseanimalsareofsosimpleastructure,thatCuvierhasarrangedthemwiththeintestinalworms,thoughneverfoundwithinthebodiesofotheranimals。 Numerousspeciesinhabitbothsaltandfreshwater;butthosetowhichIalludewerefound,eveninthedrierpartsoftheforest,beneathlogsofrottenwood,onwhichIbelievetheyfeed。Ingeneralformtheyresemblelittleslugs,butareverymuchnarrowerinproportion,andseveralofthespeciesarebeautifullycolouredwithlongitudinalstripes。Theirstructureisverysimple:nearthemiddleoftheunderorcrawlingsurfacetherearetwosmalltransverseslits,fromtheanterioroneofwhichafunnel- shapedandhighlyirritablemouthcanbeprotruded。Forsometimeaftertherestoftheanimalwascompletelydeadfromtheeffectsofsaltwateroranyothercause,thisorganstillretaineditsvitality。 IfoundnolessthantwelvedifferentspeciesofterrestrialPlanariaeindifferentpartsofthesouthernhemisphere。[3]SomespecimenswhichIobtainedatVanDieman’sLand,Ikeptalivefornearlytwomonths,feedingthemonrottenwood。Havingcutoneofthemtransverselyintotwonearlyequalparts,inthecourseofafortnightbothhadtheshapeofperfectanimals。Ihad,however,sodividedthebody,thatoneofthehalvescontainedboththeinferiororifices,andtheother,inconsequence,none。Inthecourseoftwenty-fivedaysfromtheoperation,themoreperfecthalfcouldnothavebeendistinguishedfromanyotherspecimen。Theotherhadincreasedmuchinsize;andtowardsitsposteriorend,aclearspacewasformedintheparenchymatousmass,inwhicharudimentarycup-shapedmouthcouldclearlybedistinguished;ontheundersurface,however,nocorrespondingslitwasyetopen。Iftheincreasedheatoftheweather,asweapproachedtheequator,hadnotdestroyedalltheindividuals,therecanbenodoubtthatthislaststepwouldhavecompleteditsstructure。 Althoughsowell-knownanexperiment,itwasinterestingtowatchthegradualproductionofeveryessentialorgan,outofthesimpleextremityofanotheranimal。ItisextremelydifficulttopreservethesePlanariae;assoonasthecessationoflifeallowstheordinarylawsofchangetoact,theirentirebodiesbecomesoftandfluid,witharapiditywhichIhaveneverseenequalled。 IfirstvisitedtheforestinwhichthesePlanariaewerefound,incompanywithanoldPortuguesepriestwhotookmeouttohuntwithhim。Thesportconsistedinturningintothecoverafewdogs,andthenpatientlywaitingtofireatanyanimalwhichmightappear。Wewereaccompaniedbythesonofaneighbouringfarmer——agoodspecimenofawildBrazilianyouth。 Hewasdressedinatatteredoldshirtandtrousers,andhadhisheaduncovered: hecarriedanold-fashionedgunandalargeknife。Thehabitofcarryingtheknifeisuniversal;andintraversingathickwooditisalmostnecessary,onaccountofthecreepingplants。Thefrequentoccurrenceofmurdermaybepartlyattributedtothishabit。TheBraziliansaresodexterouswiththeknife,thattheycanthrowittosomedistancewithprecision,andwithsufficientforcetocauseafatalwound。Ihaveseenanumberoflittleboyspractisingthisartasagameofplayandfromtheirskillinhittinganuprightstick,theypromisedwellformoreearnestattempts。Mycompanion,thedaybefore,hadshottwolargebeardedmonkeys。Theseanimalshaveprehensiletails,theextremityofwhich,evenafterdeath,cansupportthewholeweightofthebody。Oneofthemthusremainedfasttoabranch,anditwasnecessarytocutdownalargetreetoprocureit。Thiswassooneffected,anddowncametreeandmonkeywithanawfulcrash。Ourday’ssport,besidesthemonkey,wasconfinedtosundrysmallgreenparrotsandafewtoucans。Iprofited,however,bymyacquaintancewiththePortuguesepadre,foronanotheroccasionhegavemeafinespecimenoftheYagouaroundicat。 EveryonehasheardofthebeautyofthescenerynearBotofogo。ThehouseinwhichIlivedwasseatedclosebeneaththewell-knownmountainoftheCorcovado。Ithasbeenremarked,withmuchtruth,thatabruptlyconicalhillsarecharacteristicoftheformationwhichHumboldtdesignatesasgneiss-granite。Nothingcanbemorestrikingthantheeffectofthesehugeroundedmassesofnakedrockrisingoutofthemostluxuriantvegetation。 Iwasofteninterestedbywatchingtheclouds,which,rollinginfromseaward,formedabankjustbeneaththehighestpointoftheCorcovado。 Thismountain,likemostothers,whenthuspartlyveiled,appearedtorisetoafarprouderelevationthanitsrealheightof2300feet。Mr。Daniellhasobserved,inhismeteorologicalessays,thatacloudsometimesappearsfixedonamountainsummit,whilethewindcontinuestoblowoverit。Thesamephenomenonherepresentedaslightlydifferentappearance。Inthiscasethecloudwasclearlyseentocurlover,andrapidlypassbythesummit,andyetwasneitherdiminishednorincreasedinsize。Thesunwassetting,andagentlesoutherlybreeze,strikingagainstthesouthernsideoftherock,mingleditscurrentwiththecolderairabove;andthevapourwasthuscondensed;butasthelightwreathsofcloudpassedovertheridge,andcamewithintheinfluenceofthewarmeratmosphereofthenorthernslopingbank,theywereimmediatelyre-dissolved。 Theclimate,duringthemonthsofMayandJune,orthebeginningofwinter,wasdelightful。Themeantemperature,fromobservationstakenatnineo’clock,bothmorningandevening,wasonly72degs。Itoftenrainedheavily,butthedryingsoutherlywindssoonagainrenderedthewalkspleasant。 Onemorning,inthecourseofsixhours,1。6inchesofrainfell。AsthisstormpassedovertheforestswhichsurroundtheCorcovado,thesoundproducedbythedropspatteringonthecountlessmultitudeofleaveswasveryremarkable,itcouldbeheardatthedistanceofaquarterofamile,andwasliketherushingofagreatbodyofwater。Afterthehotterdays,itwasdelicioustositquietlyinthegardenandwatchtheeveningpassintonight。Nature,intheseclimes,chooseshervocalistsfrommorehumbleperformersthaninEurope。Asmallfrog,ofthegenusHyla,sitsonabladeofgrassaboutaninchabovethesurfaceofthewater,andsendsforthapleasingchirp: whenseveralaretogethertheysinginharmonyondifferentnotes。Ihadsomedifficultyincatchingaspecimenofthisfrog。ThegenusHylahasitstoesterminatedbysmallsuckers;andIfoundthisanimalcouldcrawlupapaneofglass,whenplacedabsolutelyperpendicular。Variouscicidaeandcrickets,atthesametime,keepupaceaselessshrillcry,butwhich,softenedbythedistance,isnotunpleasant。Everyeveningafterdarkthisgreatconcertcommenced;andoftenhaveIsatlisteningtoit,untilmyattentionhasbeendrawnawaybysomecuriouspassinginsect。 Atthesetimesthefirefliesareseenflittingaboutfromhedgetohedge。 Onadarknightthelightcanbeseenatabouttwohundredpacesdistant。 Itisremarkablethatinallthedifferentkindsofglowworms,shiningelaters,andvariousmarineanimals(suchasthecrustacea,medusae,nereidae,acorallineofthegenusClytia,andPyrosma),whichIhaveobserved,thelighthasbeenofawell-markedgreencolour。Allthefireflies,whichIcaughthere,belongedtotheLampyridae(inwhichfamilytheEnglishglowwormisincluded),andthegreaternumberofspecimenswereofLampyrisoccidentalis。[4]Ifoundthatthisinsectemittedthemostbrilliantflasheswhenirritated:intheintervals,theabdominalringswereobscured。Theflashwasalmostco-instantaneousinthetworings,butitwasjustperceptiblefirstintheanteriorone。Theshiningmatterwasfluidandveryadhesive:littlespots,wheretheskinhadbeentorn,continuedbrightwithaslightscintillation,whilsttheuninjuredpartswereobscured。Whentheinsectwasdecapitatedtheringsremaineduninterruptedlybright,butnotsobrilliantasbefore:localirritationwithaneedlealwaysincreasedthevividnessofthelight。Theringsinoneinstanceretainedtheirluminouspropertynearlytwenty-fourhoursafterthedeathoftheinsect。Fromthesefactsitwouldappearprobable,thattheanimalhasonlythepowerofconcealingorextinguishingthelightforshortintervals,andthatatothertimesthedisplayisinvoluntary。Onthemuddyandwetgravel-walksIfoundthelarvaeofthislampyrisingreatnumbers:theyresembledingeneralformthefemaleoftheEnglishglowworm。Theselarvaepossessedbutfeebleluminouspowers;verydifferentlyfromtheirparents,ontheslightesttouchtheyfeigneddeathandceasedtoshine;nordidirritationexciteanyfreshdisplay。Ikeptseveralofthemaliveforsometime:theirtailsareverysingularorgans,fortheyact,byawell-fittedcontrivance,assuckersororgansofattachment,andlikewiseasreservoirsforsaliva,orsomesuchfluid。Irepeatedlyfedthemonrawmeat;andIinvariablyobserved,thateverynowandthentheextremityofthetailwasappliedtothemouth,andadropoffluidexudedonthemeat,whichwasthenintheactofbeingconsumed。Thetail,notwithstandingsomuchpractice,doesnotseemtobeabletofinditswaytothemouth;atleasttheneckwasalwaystouchedfirst,andapparentlyasaguide。 WhenwewereatBahia,anelaterorbeetle(Pyrophorusluminosus,Illig。) seemedthemostcommonluminousinsect。Thelightinthiscasewasalsorenderedmorebrilliantbyirritation。Iamusedmyselfonedaybyobservingthespringingpowersofthisinsect,whichhavenot,asitappearstome,beenproperlydescribed。[5]Theelater,whenplacedonitsbackandpreparingtospring,moveditsheadandthoraxbackwards,sothatthepectoralspinewasdrawnout,andrestedontheedgeofitssheath。Thesamebackwardmovementbeingcontinued,thespine,bythefullactionofthemuscles,wasbentlikeaspring;andtheinsectatthismomentrestedontheextremityofitsheadandwing-cases。Theeffortbeingsuddenlyrelaxed,theheadandthoraxflewup,andinconsequence,thebaseofthewing-casesstruckthesupportingsurfacewithsuchforce,thattheinsectbythereactionwasjerkedupwardstotheheightofoneortwoinches。 Theprojectingpointsofthethorax,andthesheathofthespine,servedtosteadythewholebodyduringthespring。InthedescriptionswhichI