Ofterrestrialmammals，thereisonlyonewhichmustbeconsideredasindigenous，namely，amouseMusGalapagoensis，andthisisconfined，asfarasIcouldascertain，toChathamIsland，themosteasterlyislandofthegroup。Itbelongs，asIaminformedbyMr。Waterhouse，toadivisionofthefamilyofmicecharacteristicofAmerica。AtJamesIsland，thereisaratsufficientlydistinctfromthecommonkindtohavebeennamedanddescribedbyMr。Waterhouse；butasitbelongstotheold-worlddivisionofthefamily，andasthisislandhasbeenfrequentedbyshipsforthelasthundredandfiftyyears，Icanhardlydoubtthatthisratismerelyavarietyproducedbythenewandpeculiarclimate，food，andsoil，towhichithasbeensubjected。Althoughnoonehasarighttospeculatewithoutdistinctfacts，yetevenwithrespecttotheChathamIslandmouse，itshouldbeborneinmind，thatitmaypossiblybeanAmericanspeciesimportedhere；forIhaveseen，inamostunfrequentedpartofthePampas，anativemouselivingintheroofofanewlybuilthovel，andthereforeitstransportationinavesselisnotimprobable：analogousfactshavebeenobservedbyDr。
　　RichardsoninNorthAmerica。
　　Ofland-birdsIobtainedtwenty-sixkinds，allpeculiartothegroupandfoundnowhereelse，withtheexceptionofonelark-likefinchfromNorthAmericaDolichonyxoryzivorus，whichrangesonthatcontinentasfarnorthas54degs。，andgenerallyfrequentsmarshes。Theothertwenty-fivebirdsconsist，firstly，ofahawk，curiouslyintermediateinstructurebetweenabuzzardandtheAmericangroupofcarrion-feedingPolybori；andwiththeselatterbirdsitagreesmostcloselyineveryhabitandeventoneofvoice。Secondly，therearetwoowls，representingtheshort-earedandwhitebarn-owlsofEurope。Thirdly，awren，threetyrant-flycatcherstwoofthemspeciesofPyrocephalus，oneorbothofwhichwouldberankedbysomeornithologistsasonlyvarieties，andadove——allanalogousto，butdistinctfrom，Americanspecies。Fourthly，aswallow，whichthoughdifferingfromthePrognepurpureaofbothAmericas，onlyinbeingratherdullercolored，smaller，andslenderer，isconsideredbyMr。Gouldasspecificallydistinct。Fifthly，therearethreespeciesofmockingthrush——aformhighlycharacteristicofAmerica。Theremainingland-birdsformamostsingulargroupoffinches，relatedtoeachotherinthestructureoftheirbeaks，shorttails，formofbodyandplumage：therearethirteenspecies，whichMr。Gouldhasdividedintofoursubgroups。Allthesespeciesarepeculiartothisarchipelago；andsoisthewholegroup，withtheexceptionofonespeciesofthesub-groupCactornis，latelybroughtfromBowIsland，intheLowArchipelago。OfCactornis，thetwospeciesmaybeoftenseenclimbingabouttheflowersofthegreatcactus-trees；butalltheotherspeciesofthisgroupoffinches，mingledtogetherinflocks，feedonthedryandsterilegroundofthelowerdistricts。Themalesofall，orcertainlyofthegreaternumber，arejetblack；andthefemaleswithperhapsoneortwoexceptionsarebrown。ThemostcuriousfactistheperfectgradationinthesizeofthebeaksinthedifferentspeciesofGeospiza，fromoneaslargeasthatofahawfinchtothatofachaffinch，andifMr。Gouldisrightinincludinghissub-group，Certhidea，inthemaingroupeventothatofawarbler。ThelargestbeakinthegenusGeospizaisshowninFig。1，andthesmallestinFig。3；butinsteadoftherebeingonlyoneintermediatespecies，withabeakofthesizeshowninFig。2，therearenolessthansixspecieswithinsensiblygraduatedbeaks。Thebeakofthesub-groupCerthidea，isshowninFig。4。ThebeakofCactornisis[picture]
　　1。Geospizamagnirostris。2。Geospizafortis。3。Geospizaparvula。4。
　　Certhideaolivasea。
　　somewhatlikethatofastarling，andthatofthefourthsubgroup，Camarhynchus，isslightlyparrot-shaped。Seeingthisgradationanddiversityofstructureinonesmall，intimatelyrelatedgroupofbirds，onemightreallyfancythatfromanoriginalpaucityofbirdsinthisarchipelago，onespecieshadbeentakenandmodifiedfordifferentends。Inalikemanneritmightbefanciedthatabirdoriginallyabuzzard，hadbeeninducedheretoundertaketheofficeofthecarrion-feedingPolyborioftheAmericancontinent。
　　Ofwadersandwater-birdsIwasabletogetonlyelevenkinds，andoftheseonlythreeincludingarailconfinedtothedampsummitsoftheislandsarenewspecies。Consideringthewanderinghabitsofthegulls，Iwassurprisedtofindthatthespeciesinhabitingtheseislandsispeculiar，butalliedtoonefromthesouthernpartsofSouthAmerica。Thefargreaterpeculiarityoftheland-birds，namely，twenty-fiveoutoftwenty-six，beingnewspecies，oratleastnewraces，comparedwiththewadersandweb-footedbirds，isinaccordancewiththegreaterrangewhichtheselatterordershaveinallpartsoftheworld。Weshallhereafterseethislawofaquaticforms，whethermarineorfreshwater，beinglesspeculiaratanygivenpointoftheearth’ssurfacethantheterrestrialformsofthesameclasses，strikinglyillustratedintheshells，andinalesserdegreeintheinsectsofthisarchipelago。
　　Twoofthewadersarerathersmallerthanthesamespeciesbroughtfromotherplaces：theswallowisalsosmaller，thoughitisdoubtfulwhetherornotitisdistinctfromitsanalogue。Thetwoowls，thetwotyrant-catchersPyrocephalusandthedove，arealsosmallerthantheanalogousbutdistinctspecies，towhichtheyaremostnearlyrelated；ontheotherhand，thegullisratherlarger。Thetwoowls，theswallow，allthreespeciesofmocking-thrush，thedoveinitsseparatecoloursthoughnotinitswholeplumage，theTotanus，andthegull，arelikewiseduskiercolouredthantheiranalogousspecies；andinthecaseofthemocking-thrushandTotanus，thananyotherspeciesofthetwogenera。Withtheexceptionofawrenwithafineyellowbreast，andofatyrant-flycatcherwithascarlettuftandbreast，noneofthebirdsarebrilliantlycoloured，asmighthavebeenexpectedinanequatorialdistrict。Henceitwouldappearprobable，thatthesamecauseswhichheremaketheimmigrantsofsomepeculiarspeciessmaller，makemostofthepeculiarGalapageianspeciesalsosmaller，aswellasverygenerallymoreduskycoloured。Alltheplantshaveawretched，weedyappearance，andIdidnotseeonebeautifulflower。Theinsects，again，aresmall-sizedanddull-coloured，and，asMr。Waterhouseinformsme，thereisnothingintheirgeneralappearancewhichwouldhaveledhimtoimaginethattheyhadcomefromundertheequator。[1]Thebirds，plants，andinsectshaveadesertcharacter，andarenotmorebrilliantlycolouredthanthosefromsouthernPatagonia；wemay，therefore，concludethattheusualgaudycolouringoftheinter-tropicalproductions，isnotrelatedeithertotheheatorlightofthosezones，buttosomeothercause，perhapstotheconditionsofexistencebeinggenerallyfavourabletolife。
　　Wewillnowturntotheorderofreptiles，whichgivesthemoststrikingcharactertothezoologyoftheseislands。Thespeciesarenotnumerous，butthenumbersofindividualsofeachspeciesareextraordinarilygreat。
　　ThereisonesmalllizardbelongingtoaSouthAmericangenus，andtwospeciesandprobablymoreoftheAmblyrhynchus——agenusconfinedtotheGalapagosIslands。Thereisonesnakewhichisnumerous；itisidentical，asIaminformedbyM。Bibron，withthePsammophisTemminckiifromChile。[2]Ofsea-turtleIbelievetherearemorethanonespecies，andoftortoisesthereare，asweshallpresentlyshow，twoorthreespeciesorraces。Oftoadsandfrogstherearenone：Iwassurprisedatthis，consideringhowwellsuitedforthemthetemperateanddampupperwoodsappearedtobe。ItrecalledtomymindtheremarkmadebyBorySt。
　　Vincent，[3]namely，thatnoneofthisfamilyarefoundonanyofthevolcanicislandsinthegreatoceans。AsfarasIcanascertainfromvariousworks，thisseemstoholdgoodthroughoutthePacific，andeveninthelargeislandsoftheSandwicharchipelago。Mauritiusoffersanapparentexception，whereIsawtheRanaMascariensisinabundance：
　　thisfrogissaidnowtoinhabittheSeychelles，Madagascar，andBourbon；
　　butontheotherhand，DuBois，inhisvoyagein1669，statesthattherewerenoreptilesinBourbonexcepttortoises；andtheOfficierduRoiassertsthatbefore1768ithadbeenattempted，withoutsuccess，tointroducefrogsintoMauritius——Ipresumeforthepurposeofeating：henceitmaybewelldoubtedwhetherthisfrogisanaboriginaloftheseislands。Theabsenceofthefrogfamilyintheoceanicislandsisthemoreremarkable，whencontrastedwiththecaseoflizards，whichswarmonmostofthesmallestislands。Maythisdifferencenotbecaused，bythegreaterfacilitywithwhichtheeggsoflizards，protectedbycalcareousshellsmightbetransportedthroughsalt-water，thancouldtheslimyspawnoffrogs？
　　IwillfirstdescribethehabitsofthetortoiseTestudonigra，formerlycalledIndica，whichhasbeensofrequentlyalludedto。Theseanimalsarefound，Ibelieve，onalltheislandsofthearchipelago；certainlyonthegreaternumber。Theyfrequentinpreferencethehighdampparts，buttheylikewiseliveinthelowerandariddistricts。Ihavealreadyshown，fromthenumberswhichhavebeencaughtinasingleday，howverynumeroustheymustbe。Somegrowtoanimmensesize：Mr。Lawson，anEnglishman，andvice-governorofthecolony，toldusthathehadseenseveralsolarge，thatitrequiredsixoreightmentoliftthemfromtheground；andthatsomehadaffordedasmuchastwohundredpoundsofmeat。Theoldmalesarethelargest，thefemalesrarelygrowingtosogreatasize：themalecanreadilybedistinguishedfromthefemalebythegreaterlengthofitstail。Thetortoiseswhichliveonthoseislandswherethereisnowater，orinthelowerandaridpartsoftheothers，feedchieflyonthesucculentcactus。Thosewhichfrequentthehigheranddampregions，eattheleavesofvarioustrees，akindofberrycalledguayavitawhichisacidandaustere，andlikewiseapalegreenfilamentouslichenUsneraplicata，thathangsfromtheboughsofthetrees。
　　Thetortoiseisveryfondofwater，drinkinglargequantities，andwallowinginthemud。Thelargerislandsalonepossesssprings，andthesearealwayssituatedtowardsthecentralparts，andataconsiderableheight。Thetortoises，therefore，whichfrequentthelowerdistricts，whenthirsty，areobligedtotravelfromalongdistance。Hencebroadandwell-beatenpathsbranchoffineverydirectionfromthewellsdowntothesea-coast；andtheSpaniardsbyfollowingthemup，firstdiscoveredthewatering-places。WhenIlandedatChathamIsland，Icouldnotimaginewhatanimaltravelledsomethodicallyalongwell-chosentracks。Nearthespringsitwasacuriousspectacletobeholdmanyofthesehugecreatures，oneseteagerlytravellingonwardswithoutstretchednecks，andanothersetreturning，afterhavingdrunktheirfill。Whenthetortoisearrivesatthespring，quiteregardlessofanyspectator，heburieshisheadinthewaterabovehiseyes，andgreedilyswallowsgreatmouthfuls，attherateofaboutteninaminute。Theinhabitantssayeachanimalstaysthreeorfourdaysintheneighbourhoodofthewater，andthenreturnstothelowercountry；buttheydifferedrespectingthefrequencyofthesevisits。Theanimalprobablyregulatesthemaccordingtothenatureofthefoodonwhichithaslived。Itis，however，certain，thattortoisescansubsistevenontheseislandswherethereisnootherwaterthanwhatfallsduringafewrainydaysintheyear。
　　Ibelieveitiswellascertained，thatthebladderofthefrogactsasareservoirforthemoisturenecessarytoitsexistence：suchseemstobethecasewiththetortoise。Forsometimeafteravisittothesprings，theirurinarybladdersaredistendedwithfluid，whichissaidgraduallytodecreaseinvolume，andtobecomelesspure。Theinhabitants，whenwalkinginthelowerdistrict，andovercomewiththirst，oftentakeadvantageofthiscircumstance，anddrinkthecontentsofthebladderiffull：inoneIsawkilled，thefluidwasquitelimpid，andhadonlyaveryslightlybittertaste。Theinhabitants，however，alwaysfirstdrinkthewaterinthepericardium，whichisdescribedasbeingbest。
　　Thetortoises，whenpurposelymovingtowardsanypoint，travelbynightandday，andarriveattheirjourney’sendmuchsoonerthanwouldbeexpected。
　　Theinhabitants，fromobservingmarkedindividuals，considerthattheytraveladistanceofabouteightmilesintwoorthreedays。Onelargetortoise，whichIwatched，walkedattherateofsixtyyardsintenminutes，thatis360yardsinthehour，orfourmilesaday，——allowingalittletimeforittoeatontheroad。Duringthebreedingseason，whenthemaleandfemalearetogether，themaleuttersahoarseroarorbellowing，which，itissaid，canbeheardatthedistanceofmorethanahundredyards。
　　Thefemaleneveruseshervoice，andthemaleonlyatthesetimes；sothatwhenthepeoplehearthisnoise，theyknowthatthetwoaretogether。TheywereatthistimeOctoberlayingtheireggs。Thefemale，wherethesoilissandy，depositsthemtogether，andcoversthemupwithsand；butwherethegroundisrockyshedropsthemindiscriminatelyinanyhole：Mr。Bynoefoundsevenplacedinafissure。Theeggiswhiteandspherical；onewhichImeasuredwasseveninchesandthree-eighthsincircumference，andthereforelargerthanahen’segg。Theyoungtortoises，assoonastheyarehatched，fallapreyingreatnumberstothecarrion-feedingbuzzard。Theoldonesseemgenerallytodiefromaccidents，asfromfallingdownprecipices：
　　atleast，severaloftheinhabitantstoldme，thattheyneverfoundonedeadwithoutsomeevidentcause。