Thenaturalistwillobtainaclearerideaofthevarietyandinterestoftheproductionsofthiscountry，bythestatement，thatitslandbirdsbelongto108genera，ofwhich20areexclusivelycharacteristicofit；while35belongtothatlimitedareawhichincludestheMoluccasandNorthAustralia，andwhosespeciesofthesegenerahavebeenentirelyderivedfromNewGuinea。Aboutone-halfoftheNewGuineageneraarefoundalsoinAustralia，aboutone-thirdinIndiaandtheIndo-Malayislands。
Averycuriousfact，nothithertosufficientlynoticed，istheappearanceofapureMalayelementinthebirdsofNewGuinea。WefindtwospeciesofEupetes，acuriousMalayangenusalliedtotheforked-tailwater-chats；twoofAlcippe，anIndianandMalaywren-likeform；anArachnothera，quiteresemblingthespider-
catchinghoneysuckersofMalacca；twospeciesofGracula，theMynahsofIndia；andacuriouslittleblackPrionochilus，asaw-
billedfruitpecker，undoubtedlyalliedtotheMalayanform，althoughperhapsadistinctgenus。Nownotoneofthesebirds，oranythingalliedtothem，occursintheMoluccas，orwithoneexceptioninCelebesorAustralia；andastheyaremostofthembirdsofshortflight，itisverydifficulttoconceivehoworwhentheycouldhavecrossedthespaceofmorethanathousandmiles，whichnowseparatesthemfromtheirnearestallies。Suchfactspointtochangesoflandandseaonalargescale，andataratewhich，measuredbythetimerequiredforachangeofspecies，mustbetermedrapid。Byspeculatingonsuchchanges，wemayeasilyseehowpartialwavesofimmigrationmayhaveenteredNewGuinea，andhowalltraceoftheirpassagemayhavebeenobliteratedbythesubsequentdisappearanceoftheinterveningland。
Thereisnothingthatthestudyofgeologyteachesusthatismorecertainormoreimpressivethantheextremeinstabilityoftheearth\'ssurface。Everywherebeneathourfeetwefindproofsthatwhatislandhasbeensea，andthatwhereoceansnowspreadouthasoncebeenland；andthatthischangefromseatoland，andfromlandtosea，hastakenplace，notonceortwiceonly，butagainandagain，duringcountlessagesofpasttime。Nowthestudyofthedistributionofanimallifeuponthepresentsurfaceoftheearth，causesustolookuponthisconstantinterchangeoflandandsea——thismakingandunmakingofcontinents，thiselevationanddisappearanceofislands——asapotentreality，whichhasalwaysandeverywherebeeninprogress，andhasbeenthemainagentindeterminingthemannerinwhichlivingthingsarenowgroupedandscatteredovertheearth\'ssurface。Andwhenwecontinuallycomeuponsuchlittleanomaliesofdistributionasthatjustnowdescribed，wefindtheonlyrationalexplanationofthem，inthoserepeatedelevationsanddepressionswhichhavelefttheirrecordinmysterious，butstillintelligiblecharactersonthefaceoforganicnature。