Ofterrestrialmammals，thereisonlyonewhichmustbeconsideredasindigenous，namely，amouse(MusGalapagoensis)，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-likefinchfromNorthAmerica(Dolichonyxoryzivorus)，whichrangesonthatcontinentasfarnorthas54degs。，andgenerallyfrequentsmarshes。Theothertwenty-fivebirdsconsist，firstly，ofahawk，curiouslyintermediateinstructurebetweenabuzzardandtheAmericangroupofcarrion-feedingPolybori；andwiththeselatterbirdsitagreesmostcloselyineveryhabitandeventoneofvoice。Secondly，therearetwoowls，representingtheshort-earedandwhitebarn-owlsofEurope。Thirdly，awren，threetyrant-flycatchers(twoofthemspeciesofPyrocephalus，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；andthefemales(withperhapsoneortwoexceptions)arebrown。ThemostcuriousfactistheperfectgradationinthesizeofthebeaksinthedifferentspeciesofGeospiza，fromoneaslargeasthatofahawfinchtothatofachaffinch，and(ifMr。Gouldisrightinincludinghissub-group，Certhidea，inthemaingroup)eventothatofawarbler。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，andoftheseonlythree(includingarailconfinedtothedampsummitsoftheislands)arenewspecies。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-catchers(Pyrocephalus)andthedove，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，andtwospecies(andprobablymore)oftheAmblyrhynchus——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？
Iwillfirstdescribethehabitsofthetortoise(Testudonigra，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，akindofberry(calledguayavita)whichisacidandaustere，andlikewiseapalegreenfilamentouslichen(Usneraplicata)，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。Theywereatthistime(October)layingtheireggs。Thefemale，wherethesoilissandy，depositsthemtogether，andcoversthemupwithsand；butwherethegroundisrockyshedropsthemindiscriminatelyinanyhole：Mr。Bynoefoundsevenplacedinafissure。Theeggiswhiteandspherical；onewhichImeasuredwasseveninchesandthree-eighthsincircumference，andthereforelargerthanahen’segg。Theyoungtortoises，assoonastheyarehatched，fallapreyingreatnumberstothecarrion-feedingbuzzard。Theoldonesseemgenerallytodiefromaccidents，asfromfallingdownprecipices：
atleast，severaloftheinhabitantstoldme，thattheyneverfoundonedeadwithoutsomeevidentcause。
