第35章

类别:其他 作者:Charles Darwin字数:5563更新时间:18/12/21 17:23:57
Ihaveseen,intheCordilleraoftheAndes,theevidentmarkswherestupendousmountainshavebeenbrokenintopieceslikesomuchthincrust,andthestratathrownontheirverticaledges;butneverdidanyscene,likethese“streamsofstones。”soforciblyconveytomymindtheideaofaconvulsion,ofwhichinhistoricalrecordswemightinvainseekforanycounterpart: yettheprogressofknowledgewillprobablysomedaygiveasimpleexplanationofthisphenomenon,asitalreadyhasofthesolong-thoughtinexplicabletransportaloftheerraticboulders,whicharestrewedovertheplainsofEurope。 Ihavelittletoremarkonthezoologyoftheseislands。Ihavebeforedescribedthecarrion-vultureofPolyborus。Therearesomeotherhawks,owls,andafewsmallland-birds。Thewater-fowlareparticularlynumerous,andtheymustformerly,fromtheaccountsoftheoldnavigators,havebeenmuchmoreso。OnedayIobservedacormorantplayingwithafishwhichithadcaught。Eighttimessuccessivelythebirdletitspreygo,thendivedafterit,andalthoughindeepwater,broughtiteachtimetothesurface。IntheZoologicalGardensIhaveseentheottertreatafishinthesamemanner,muchasacatdoesamouse:IdonotknowofanyotherinstancewheredameNatureappearssowilfullycruel。Anotherday,havingplacedmyselfbetweenapenguin(Aptenodytesdemersa)andthewater,I wasmuchamusedbywatchingitshabits。Itwasabravebird;andtillreachingthesea,itregularlyfoughtanddrovemebackwards。Nothinglessthanheavyblowswouldhavestoppedhim;everyinchhegainedhefirmlykept,standingclosebeforemeerectanddetermined。Whenthusopposedhecontinuallyrolledhisheadfromsidetoside,inaveryoddmanner,asifthepowerofdistinctvisionlayonlyintheanteriorandbasalpartofeacheye。 Thisbirdiscommonlycalledthejackasspenguin,fromitshabit,whileonshore,ofthrowingitsheadbackwards,andmakingaloudstrangenoise,verylikethebrayingofanass;butwhileatsea,andundisturbed,itsnoteisverydeepandsolemn,andisoftenheardinthenight-time。Indiving,itslittlewingsareusedasfins;butontheland,asfrontlegs。 Whencrawling,itmaybesaidonfourlegs,throughthetussocksoronthesideofagrassycliff,itmovessoveryquicklythatitmighteasilybemistakenforaquadruped。Whenatseaandfishing,itcomestothesurfaceforthepurposeofbreathingwithsuchaspring,anddivesagainsoinstantaneously,thatIdefyanyoneatfirstsighttobesurethatitwasnotafishleapingforsport。 TwokindsofgeesefrequenttheFalklands。Theuplandspecies(AnasMagellanica)iscommon,inpairsandinsmallflocks,throughouttheisland。 Theydonotmigrate,butbuildonthesmalloutlyingislets。Thisissupposedtobefromfearofthefoxes:anditisperhapsfromthesamecausethatthesebirds,thoughverytamebyday,areshyandwildintheduskoftheevening。Theyliveentirelyonvegetablematter。 Therock-goose,socalledfromlivingexclusivelyonthesea-beach(Anasantarctica),iscommonbothhereandonthewestcoastofAmerica,asfarnorthasChile。InthedeepandretiredchannelsofTierradelFuego,thesnow-whitegander,invariablyaccompaniedbyhisdarkerconsort,andstandingclosebyeachotheronsomedistantrockypoint,isacommonfeatureinthelandscape。 Intheseislandsagreatloggerheadedduckorgoose(Anasbrachyptera),whichsometimesweighstwenty-twopounds,isveryabundant。Thesebirdswereinformerdayscalled,fromtheirextraordinarymannerofpaddlingandsplashinguponthewater,race-horses;butnowtheyarenamed,muchmoreappropriately,steamers。Theirwingsaretoosmallandweaktoallowofflight,butbytheiraid,partlyswimmingandpartlyflappingthesurfaceofthewater,theymoveveryquickly。Themannerissomethinglikethatbywhichthecommonhouse-duckescapeswhenpursuedbyadog;butIamnearlysurethatthesteamermovesitswingsalternately,insteadofbothtogether,asinotherbirds。Theseclumsy,loggerheadedducksmakesuchanoiseandsplashing,thattheeffectisexceedinglycurious。 ThuswefindinSouthAmericathreebirdswhichusetheirwingsforotherpurposesbesidesflight;thepenguinsasfins,thesteameraspaddles,andtheostrichassails:andtheApteryzofNewZealand,aswellasitsgiganticextinctprototypetheDeinornis,possessonlyrudimentaryrepresentativesofwings。Thesteamerisabletodiveonlytoaveryshortdistance。Itfeedsentirelyonshell-fishfromthekelpandtidalrocks:hencethebeakandhead,forthepurposeofbreakingthem,aresurprisinglyheavyandstrong:theheadissostrongthatIhavescarcelybeenabletofractureitwithmygeologicalhammer;andalloursportsmensoondiscoveredhowtenaciousthesebirdswereoflife。Whenintheeveningplumingthemselvesinaflock,theymakethesameoddmixtureofsoundswhichbull-frogsdowithinthetropics。 InTierradelFuego,aswellasintheFalklandIslands,Imademanyobservationsonthelowermarineanimals,[11]buttheyareoflittlegeneralinterest。Iwillmentiononlyoneclassoffacts,relatingtocertainzoophytesinthemorehighlyorganizeddivisionofthatclass。Severalgenera(Flustra,Eschara,Cellaria,Crisia,andothers) agreeinhavingsingularmoveableorgans(likethoseofFlustraavicularia,foundintheEuropeanseas)attachedtotheircells。Theorgan,inthegreaternumberofcases,verycloselyresemblestheheadofavulture; butthelowermandiblecanbeopenedmuchwiderthaninarealbird’sbeak。 Theheaditselfpossessesconsiderablepowersofmovement,bymeansofashortneck。Inonezoophytetheheaditselfwasfixed,butthelowerjawfree:inanotheritwasreplacedbyatriangularhood,withabeautifully-fittedtrap-door,whichevidentlyansweredtothelowermandible。Inthegreaternumberofspecies,eachcellwasprovidedwithonehead,butinotherseachcellhadtwo。 Theyoungcellsattheendofthebranchesofthesecorallinescontainquiteimmaturepolypi,yetthevulture-headsattachedtothem,thoughsmall,areineveryrespectperfect。Whenthepolypuswasremovedbyaneedlefromanyofthecells,theseorgansdidnotappearintheleastaffected。 Whenoneofthevulture-likeheadswascutofffromthecell,thelowermandibleretaineditspowerofopeningandclosing。Perhapsthemostsingularpartoftheirstructureis,thatwhenthereweremorethantworowsofcellsonabranch,thecentralcellswerefurnishedwiththeseappendages,ofonlyone-fourththesizeoftheoutsideones。Theirmovementsvariedaccordingtothespecies;butinsomeIneversawtheleastmotion;whileothers,withthelowermandiblegenerallywideopen,oscillatedbackwardsandforwardsattherateofaboutfivesecondseachturn,othersmovedrapidlyandbystarts。Whentouchedwithaneedle,thebeakgenerallyseizedthepointsofirmly,thatthewholebranchmightbeshaken。 Thesebodieshavenorelationwhateverwiththeproductionoftheeggsorgemmules,astheyareformedbeforetheyoungpolypiappearinthecellsattheendofthegrowingbranches;astheymoveindependentlyofthepolypi,anddonotappeartobeinanywayconnectedwiththem;andastheydifferinsizeontheouterandinnerrowsofcells,Ihavelittledoubt,thatintheirfunctions,theyarerelatedrathertothehornyaxisofthebranchesthantothepolypiinthecells。Thefleshyappendageatthelowerextremityofthesea-pen(describedatBahiaBlanca)alsoformspartofthezoophyte,asawhole,inthesamemannerastherootsofatreeformpartofthewholetree,andnotoftheindividualleaforflower-buds。 Inanotherelegantlittlecoralline(Crisia?),eachcellwasfurnishedwithalong-toothedbristle,whichhadthepowerofmovingquickly。Eachofthesebristlesandeachofthevulture-likeheadsgenerallymovedquiteindependentlyoftheothers,butsometimesallonbothsidesofabranch,sometimesonlythoseononeside,movedtogethercoinstantaneously,sometimeseachmovedinregularorderoneafteranother。Intheseactionsweapparentlybeholdasperfectatransmissionofwillinthezoophyte,thoughcomposedofthousandsofdistinctpolypi,asinanysingleanimal。Thecase,indeed,isnotdifferentfromthatofthesea-pens,which,whentouched,drewthemselvesintothesandonthecoastofBahiaBlanca。Iwillstateoneotherinstanceofuniformaction,thoughofaverydifferentnature,inazoophytecloselyalliedtoClytia,andthereforeverysimplyorganized。Havingkeptalargetuftofitinabasinofsalt-water,whenitwasdarkIfoundthatasoftenasIrubbedanypartofabranch,thewholebecamestronglyphosphorescentwithagreenlight:IdonotthinkIeversawanyobjectmorebeautifullyso。Buttheremarkablecircumstancewas,thattheflashesoflightalwaysproceededupthebranches,fromthebasetowardstheextremities。 Theexaminationofthesecompoundanimalswasalwaysveryinterestingtome。Whatcanbemoreremarkablethantoseeaplant-likebodyproducinganegg,capableofswimmingaboutandofchoosingaproperplacetoadhereto,whichthensproutsintobranches,eachcrowdedwithinnumerabledistinctanimals,oftenofcomplicatedorganizations?Thebranches,moreover,aswehavejustseen,sometimespossessorganscapableofmovementandindependentofthepolypi。Surprisingasthisunionofseparateindividualsinacommonstockmustalwaysappear,everytreedisplaysthesamefact,forbudsmustbeconsideredasindividualplants。Itis,however,naturaltoconsiderapolypus,furnishedwithamouth,intestines,andotherorgans,asadistinctindividual,whereastheindividualityofaleaf-budisnoteasilyrealised; sothattheunionofseparateindividualsinacommonbodyismorestrikinginacorallinethaninatree。Ourconceptionofacompoundanimal,whereinsomerespectstheindividualityofeachisnotcompleted,maybeaided,byreflectingontheproductionoftwodistinctcreaturesbybisectingasingleonewithaknife,orwhereNatureherselfperformsthetaskofbisection。Wemayconsiderthepolypiinazoophyte,orthebudsinatree,ascaseswherethedivisionoftheindividualhasnotbeencompletelyeffected。 Certainlyinthecaseoftrees,andjudgingfromanalogyinthatofcorallines,theindividualspropagatedbybudsseemmoreintimatelyrelatedtoeachother,thaneggsorseedsaretotheirparents。Itseemsnowprettywellestablishedthatplantspropagatedbybudsallpartakeofacommondurationoflife;anditisfamiliartoeveryone,whatsingularandnumerouspeculiaritiesaretransmittedwithcertainty,bybuds,layers,andgrafts,whichbyseminalpropagationneveroronlycasuallyreappear。 [1]ThedessertsofSyriaarecharacterized,accordingtoVolney(tom。i。p。351),bywoodybushes,numerousrats,gazellesandhares。InthelandscapeofPatagonia,theguanacoreplacesthegazelle,andtheagoutithehare。 [2]Inoticedthatseveralhoursbeforeanyoneofthecondorsdied,allthelice,withwhichitwasinfested,crawledtotheoutsidefeathers。Iwasassuredthatthisalwayshappens。 [3]London’sMagazineofNat。Hist。,vol。vii。 [4]Fromaccountspublishedsinceourvoyage,andmoreespeciallyfromseveralinterestinglettersfromCapt。Sulivan,R。 N。,employedonthesurvey,itappearsthatwetookanexaggeratedviewofthebadnessoftheclimateontheseislands。ButwhenIreflectonthealmostuniversalcoveringofpeat,andonthefactofwheatseldomripeninghere,Icanhardlybelievethattheclimateinsummerissofineanddryasithaslatelybeenrepresented。 [5]Lesson’sZoologyoftheVoyageoftheCoquille,tom。i。p。168。Alltheearlyvoyagers,andespeciallyBougainville,distinctlystatethatthewolf-likefoxwastheonlynativeanimalontheisland。 Thedistinctionoftherabbitasaspecies,istakenfrompeculiaritiesinthefur,fromtheshapeofthehead,andfromtheshortnessoftheears。 ImayhereobservethatthedifferencebetweentheIrishandEnglishharerestsuponnearlysimilarcharacters,onlymorestronglymarked[6]Ihavereason,however,tosuspectthatthereisafield-mouse。ThecommonEuropeanratandmousehaveroamedfarfromthehabitationsofthesettlers。Thecommonhoghasalsorunwildononeislet;allareofablackcolour:theboarsareveryfierce,andhavegreattrunks。 [7]The“culpeu“istheCanisMagellanicusbroughthomebyCaptainKingfromtheStraitofMagellan。ItiscommoninChile。 [8]Pernety,VoyageauxIslesMalouines,p。526。 [9]“Nousn’avonspasetemoinssaisisd’etonnementalavuedel’innombrablequantitedepierresdetoutsgrandeurs,bouleverseeslesunessurlesautres,etcependentrangees,commesiellesavoienteteamonceleesnegligemmentpourremplirdesravins。Onneselassoitpasd’admirerleseffetsprodigieuxdelanature。”——Pernety,p。526。