Asnewcharacterssometimesappearbybud—variation，whichdonotoccurintheparent—speciesorinanyalliedspecies，wemayreject，atleastinthesecases，theideathattheyareduetoreversion。Nowitiswellworthwhiletoreflectmaturelyonsomestrikingcaseofbud—variation，forinstancethatofthepeach。Thistreehasbeencultivatedbythemillioninvariouspartsoftheworld，hasbeentreateddifferently，grownonitsownrootsandgraftedonvariousstocks，plantedasastandard，trainedagainstawall，orunderglass;
yeteachbudofeachsub—varietykeepstruetoitskind。Butoccasionally，atlongintervalsoftime，atreeinEngland，orunderthewidelydifferentclimateofVirginia，producesasinglebud，andthisyieldsabranchwhicheverafterwardsbearsnectarines。Nectarinesdiffer，aseveryoneknows，frompeachesintheirsmoothness，size，andflavour;andthedifferenceissogreatthatsomebotanistshavemaintainedthattheyarespecificallydistinct。Sopermanentarethecharactersthussuddenlyacquired，thatanectarineproducedbybud—variationhaspropagateditselfbyseed。Toguardagainstthesuppositionthatthereissomefundamentaldistinctionbetweenbudandseminalvariation，itiswelltobearinmindthatnectarineshavelikewisebeenproducedfromthestoneofthepeach;and，reversely，peachesfromthestoneofthenectarine。Nowisitpossibletoconceiveexternalconditionsmorecloselyalikethanthosetowhichthebudsonthesametreeareexposed？Yetonebudalone，outofthemanythousandsbornebythesametree，hassuddenly，withoutanyapparentcause，producedanectarine。Butthecaseisevenstrongerthanthis，forthesameflower—budhasyieldedafruit，one—halforone—quarteranectarine，andtheotherhalforthree—quartersapeach。Again，sevenoreightvarietiesofthepeachhaveyieldedbybud—variationnectarines:thenectarinesthusproduced，nodoubt，differalittlefromoneanother;butstilltheyarenectarines。Ofcoursetheremustbesomecause，internalorexternal，toexcitethepeach—budtochangeitsnature;butI
cannotimagineaclassoffactsbetteradaptedtoforceonourmindstheconvictionthatwhatwecalltheexternalconditionsoflifeareinmanycasesquiteinsignificantinrelationtoanyparticularvariation，incomparisonwiththeorganisationorconstitutionofthebeingwhichvaries。
ItisknownfromthelaboursofGeoffroySaint—Hilaire，andrecentlyfromthoseofDaresteandothers，thateggsofthefowl，ifshaken，placedupright，perforated，coveredinpartwithvarnish，etc。，producemonstrouschickens。
Nowthesemonstrositiesmaybesaidtobedirectlycausedbysuchunnaturalconditions，butthemodificationsthusinducedarenotofadefinitenature。
Anexcellentobserver，M。CamilleDareste（23/59。’MemoiresurlaProductionArtificielledesMonstruosites’1862pages8—12;’RecherchessurlesConditions，etc。，chezlesMonstres’1863page6。AnabstractisgivenofGeoffroy’sExperimentsbyhisson，inhis’Vie，Travaux’etc。1847page290。），remarks\"thatthevariousspeciesofmonstrositiesarenotdeterminedbyspecificcauses;theexternalagencieswhichmodifythedevelopmentoftheembryoactsolelyincausingaperturbation——aperversioninthenormalcourseofdevelopment。\"Hecomparestheresulttowhatweseeinillness:asuddenchill，forinstance，affectsoneindividualaloneoutofmany，causingeitheracold，orsore—throat，rheumatism，orinflammationofthelungsorpleura。
Contagiousmatteractsinananalogousmanner。（23/60。Paget’LecturesonSurgicalPathology’1853volume1page483。）Wemaytakeastillmorespecificinstance:sevenpigeonswerestruckbyrattle—snakes（23/61。’ResearchesupontheVenomoftheRattle—snake’January1861byDr。Mitchellpage67。）:somesufferedfromconvulsions;somehadtheirbloodcoagulated，inothersitwasperfectlyfluid;someshowedecchymosedspotsontheheart，othersontheintestines，etc。;othersagainshowednovisiblelesioninanyorgan。Itiswellknownthatexcessindrinkingcausesdifferentdiseasesindifferentmen;
butinthetropicstheeffectsofintemperancedifferfromthosecausedinacoldclimate（23/62。Mr。Sedgwick’BritishandForeignMedico—Chirurg。Review’
July1863page175。）;andinthiscaseweseethedefiniteinfluenceofoppositeconditions。Theforegoingfactsapparentlygiveusasgoodanideaaswearelikelyforalongtimetoobtain，howinmanycasesexternalconditionsactdirectly，thoughnotdefinitely，incausingmodificationsofstructure。
SUMMARY。
Therecanbenodoubt，fromthefactsgiveninthischapter，thatextremelyslightchangesintheconditionsoflifesometimes，probablyoften，actinadefinitemanneronourdomesticatedproductions;and，astheactionofchangedconditionsincausingindefinitevariabilityisaccumulative，soitmaybewiththeirdefiniteaction。Henceconsiderableanddefinitemodificationsofstructureprobablyfollowfromalteredconditionsactingduringalongseriesofgenerations。Insomefewinstancesamarkedeffecthasbeenproducedquicklyonall，ornearlyall，theindividualswhichhavebeenexposedtoamarkedchangeofclimate，food，orothercircumstance。ThishasoccurredwithEuropeanmenintheUnitedStates，withEuropeandogsinIndia，withhorsesintheFalklandIslands，apparentlywithvariousanimalsatAngora，withforeignoystersintheMediterranean，andwithmaizetransportedfromoneclimatetoanother。Wehaveseenthatthechemicalcompoundsofsomeplantsandthestateoftheirtissuesarereadilyaffectedbychangedconditions。Arelationapparentlyexistsbetweencertaincharactersandcertainconditions，sothatifthelatterbechangedthecharacterislost——aswiththecoloursofflowers，thestateofsomeculinaryplants，thefruitofthemelon，thetailoffat—tailedsheep，andthepeculiarfleecesofothersheep。
Theproductionofgalls，andthechangeofplumageinparrotswhenfedonpeculiarfoodorwheninoculatedbythepoisonofatoad，provetouswhatgreatandmysteriouschangesinstructureandcolour，maybethedefiniteresultofchemicalchangesinthenutrientfluidsortissues。
Wenowalmostcertainlyknowthatorganicbeingsinastateofnaturemaybemodifiedinvariousdefinitewaysbytheconditionstowhichtheyhavebeenlongexposed，asinthecaseofthebirdsandotheranimalsinthenorthernandsouthernUnitedStates，andofAmericantreesincomparisonwiththeirrepresentativesinEurope。Butinmanycasesitismostdifficulttodistinguishbetweenthedefiniteresultofchangedconditions，andtheaccumulationthroughnaturalselectionofindefinitevariationswhichhaveprovedserviceable。Ifitprofitedaplanttoinhabitahumidinsteadofanaridstation，afittingchangeinitsconstitutionmightpossiblyresultfromthedirectactionoftheenvironment，thoughwehavenogroundsforbelievingthatvariationsoftherightkindwouldoccurmorefrequentlywithplantsinhabitingastationalittlemorehumidthanusual，thanwithotherplants。
Whetherthestationwasunusuallydryorhumid，variationsadaptingtheplantinaslightdegreefordirectlyoppositehabitsoflifewouldoccasionallyarise，aswehavegoodreasontobelievefromwhatweactuallyseeinothercases。
Theorganisationorconstitutionofthebeingwhichisactedon，isgenerallyamuchmoreimportantelementthanthenatureofthechangedconditions，indeterminingthenatureofthevariation。Wehaveevidenceofthisintheappearanceofnearlysimilarmodificationsunderdifferentconditions，andofdifferentmodificationsunderapparentlynearlythesameconditions。Wehavestillbetterevidenceofthisincloselyparallelvarietiesbeingfrequentlyproducedfromdistinctraces，orevendistinctspecies;andinthefrequentrecurrenceofthesamemonstrosityinthesamespecies。Wehavealsoseenthatthedegreetowhichdomesticatedbirdshavevaried，doesnotstandinanycloserelationwiththeamountofchangetowhichtheyhavebeensubjected。
Torecuronceagaintobud—variations。Whenwereflectonthemillionsofbudswhichmanytreeshaveproduced，beforesomeonebudhasvaried，wearelostinwonderastowhattheprecisecauseofeachvariationcanbe。LetusrecallthecasegivenbyAndrewKnightoftheforty—year—oldtreeoftheyellowmagnumbonumplum，anoldvarietywhichhasbeenpropagatedbygraftsonvariousstocksforaverylongperiodthroughoutEuropeandNorthAmerica，andonwhichasinglebudsuddenlyproducedtheredmagnumbonum。Weshouldalsobearinmindthatdistinctvarieties，andevendistinctspecies，——asinthecaseofpeaches，nectarines，andapricots，——ofcertainrosesandcamellias，——
althoughseparatedbyavastnumberofgenerationsfromanyprogenitorincommon，andalthoughcultivatedunderdiversifiedconditions，haveyieldedbybud—variationcloselyanalogousvarieties。Whenwereflectonthesefactswebecomedeeplyimpressedwiththeconvictionthatinsuchcasesthenatureofthevariationdependsbutlittleontheconditionstowhichtheplanthasbeenexposed，andnotinanyespecialmanneronitsindividualcharacter，butmuchmoreontheinheritednatureorconstitutionofthewholegroupofalliedbeingstowhichtheplantinquestionbelongs。Wearethusdriventoconcludethatinmostcasestheconditionsoflifeplayasubordinatepartincausinganyparticularmodification;likethatwhichasparkplays，whenamassofcombustiblesburstsintoflame——thenatureoftheflamedependingonthecombustiblematter，andnotonthespark。（23/63。ProfessorWeismannarguesstronglyinfavourofthisviewinhis’Saison—DimorphismusderSchmetterlinge’1875pages40—43。）
Nodoubteachslightvariationmusthaveitsefficientcause;butitisashopelessanattempttodiscoverthecauseofeach，astosaywhyachillorapoisonaffectsonemandifferentlyfromanother。Evenwithmodificationsresultingfromthedefiniteactionoftheconditionsoflife，whenallornearlyalltheindividuals，whichhavebeensimilarlyexposed，aresimilarlyaffected，wecanrarelyseethepreciserelationbetweencauseandeffect。Inthenextchapteritwillbeshownthattheincreaseduseordisuseofvariousorgansproducesaninheritedeffect。Itwillfurtherbeseenthatcertainvariationsareboundtogetherbycorrelationaswellasbyotherlaws。Beyondthiswecannotatpresentexplaineitherthecausesornatureofthevariabilityoforganicbeings。
CHAPTER2。XXIV。
LAWSOFVARIATION——USEANDDISUSE，ETC。
NISUSFORMATIVUS，ORTHECO—ORDINATINGPOWEROFTHEORGANISATION。
ONTHEEFFECTSOFTHEINCREASEDUSEANDDISUSEOFORGANS。
CHANGEDHABITSOFLIFE。
ACCLIMATISATIONWITHANIMALSANDPLANTS。
VARIOUSMETHODSBYWHICHTHISCANBEEFFECTED。
ARRESTSOFDEVELOPMENT。
RUDIMENTARYORGANS。
InthisandthetwofollowingchaptersIshalldiscuss，aswellasthedifficultyofthesubjectpermits，theseverallawswhichgovernVariability。
Thesemaybegroupedundertheeffectsofuseanddisuse，includingchangedhabitsandacclimatisation——arrestofdevelopment——correlatedvariation——thecohesionofhomologousparts—thevariabilityofmultipleparts——compensationofgrowth——thepositionofbudswithrespecttotheaxisoftheplant——andlastly，analogousvariation。Theseseveralsubjectssograduateintooneanotherthattheirdistinctionisoftenarbitrary。
Itmaybeconvenientfirstbrieflytodiscussthatcoordinatingandreparativepowerwhichiscommon，inahigherorlowerdegree，toallorganicbeings，andwhichwasformerlydesignatedbyphysiologistsasnisusformativus。
[Blumenbachandothers（24/1。’AnEssayonGeneration’Englishtranslationpage18;Paget’LecturesonSurgicalPathology’1853volume1page209。）haveinsistedthattheprinciplewhichpermitsaHydra，whencutintofragments，todevelopitselfintotwoormoreperfectanimals，isthesamewiththatwhichcausesawoundinthehigheranimalstohealbyacicatrice。SuchcasesasthatoftheHydraareevidentlyanalogoustothespontaneousdivisionorfissiparousgenerationofthelowestanimals，andlikewisetothebuddingofplants。Betweentheseextremecasesandthatofamerecicatricewehaveeverygradation。Spallanzani（24/2。’AnEssayonAnimalReproduction’Englishtranslation1769page79。）bycuttingoffthelegsandtailofaSalamander，gotinthecourseofthreemonthssixcropsofthesemembers;sothat687
perfectboneswerereproducedbyoneanimalduringoneseason。Atwhateverpointthelimbwascutoff，thedeficientpart，andnomore，wasexactlyreproduced。Whenadiseasedbonehasbeenremoved，anewonesometimes\"graduallyassumestheregularform，andalltheattachmentsofmuscles，ligaments，etc。，becomeascompleteasbefore。\"（24/3。Carpenter’PrinciplesofComp。Physiology’1854page479。）
Thispowerofregrowthdoesnot，however，alwaysactperfectly;thereproducedtailofalizarddiffersintheformofthescalesfromthenormaltail:withcertainOrthopterousinsectsthelargehindlegsarereproducedofsmallersize（24/4。Charlesworth’Mag。ofNat。Hist。’volume11837page145。）:thewhitecicatricewhichinthehigheranimalsunitestheedgesofadeepwoundisnotformedofperfectskin，forelastictissueisnotproducedtilllongafterwards。（24/5。Paget’LecturesonSurgicalPathology’volume1page239。）
\"Theactivityofthenisusformativus，\"saysBlumenbach，\"isinaninverseratiototheageoftheorganisedbody。\"Itspowerisalsogreaterwithanimals，thelowertheystandinthescaleoforganisation;andanimalslowinthescalecorrespondwiththeembryosofhigheranimalsbelongingtothesameclass。Newport’sobservations（24/6。QuotedbyCarpenter’Comp。Phys。’page479。）affordagoodillustrationofthisfact，forhefoundthat\"myriapods，whosehighestdevelopmentscarcelycarriesthembeyondthelarvaofperfectinsects，canregeneratelimbsandantennaeuptothetimeoftheirlastmoult;\"andsocanthelarvaeoftrueinsects，but，exceptinoneorder，notinthematureinsect。SalamanderscorrespondindevelopmentwiththetadpolesorlarvaeofthetaillessBatrachians，andbothpossesstoalargeextentthepowerofregrowth;butnotsothematuretaillessBatrachians。
Absorptionoftenplaysanimportantpartintherepairofinjuries。Whenaboneisbrokenanddoesnotunite，theendsareabsorbedandrounded，sothatafalsejointisformed;oriftheendsunite，butoverlap，theprojectingpartsareremoved。（24/7。Prof。Marey’sdiscussiononthepowerofco—
adaptationinallpartsoftheorganisationisexcellent。’LaMachineAnimale’
1873chapter9。SeealsoPaget’Lectures’etc。page257。）Adislocatedbonewillformforitselfanewsocket。Displacedtendonsandvaricoseveinsexcavatenewchannelsinthebonesagainstwhichtheypress。Butabsorptioncomesintoaction，asVirchowremarks，duringthenormalgrowthofbones;
partswhicharesolidduringyouthbecomehollowedoutforthemedullarytissueastheboneincreasesinsize。Intryingtounderstandthemanywell—
adaptedcasesofregrowthwhenaidedbyabsorption，weshouldrememberthatalmostallpartsoftheorganisation，evenwhilstretainingthesameform，undergoconstantrenewal;sothatapartwhichisnotrenewedwouldbeliabletoabsorption。
Somecases，usuallyclassedundertheso—callednisusformativus，atfirstappeartocomeunderadistincthead;fornotonlyareoldstructuresreproduced，butnewstructuresareformed。Thus，afterinflammation\"falsemembranes，\"furnishedwithblood—vessels，lymphatics，andnerves，aredeveloped;orafoetusescapesfromtheFallopiantubes，andfallsintotheabdomen，\"naturepoursoutaquantityofplasticlymph，whichformsitselfintoorganisedmembrane，richlysuppliedwithblood—vessels，\"andthefoetusisnourishedforatime。Incertaincasesofhydrocephalustheopenanddangerousspacesintheskullarefilledupwithnewbones，whichinterlockbyperfectserratedsutures。（24/8。ThesecasesaregivenbyBlumenbachinhis’EssayonGeneration’pages52，54。）Butmostphysiologists，especiallyontheContinent，havenowgivenupthebeliefinplasticlymphorblastema，andVirchow（24/9。’CellularPathology’translationbyDr。Chance1860pages27，441。）maintainsthateverystructure，neworold，isformedbytheproliferationofpre—existingcells。Onthisviewfalsemembranes，likecancerousorothertumours，aremerelyabnormaldevelopmentsofnormalgrowths;andwecanthusunderstandhowitisthattheyresembleadjoiningstructures;forinstance，thata\"falsemembraneintheserouscavitiesacquiresacoveringofepitheliumexactlylikethatwhichcoverstheoriginalserousmembrane;adhesionsoftheirismaybecomeblackapparentlyfromtheproductionofpigment—cellslikethoseoftheuvea。\"（24/10。Paget’LecturesonPathology’volume11853page357。）
Nodoubtthepowerofreparation，thoughnotalwaysperfect，isanadmirableprovision，readyforvariousemergencies，evenforsuchasoccuronlyatlongintervalsoftime。（24/11。Pagetibidpage150。）Yetthispowerisnotmorewonderfulthanthegrowthanddevelopmentofeverysinglecreature，moreespeciallyofthosewhicharepropagatedbyfissiparousgeneration。Thissubjecthasbeenherenoticed，becausewemayinferthat，whenanypartororganiseithergreatlyincreasedinsizeorwhollysuppressedthroughvariationandcontinuedselection，theco—ordinatingpoweroftheorganisationwillcontinuallytendtobringagainallthepartsintoharmonywithoneanother。]
ONTHEEFFECTSOFTHEINCREASEDUSEANDDISUSEOFORGANS。
Itisnotorious，andweshallimmediatelyadduceproofs，thatincreaseduseoractionstrengthensmuscles，glands，sense—organs，etc。;andthatdisuse，ontheotherhand，weakensthem。IthasbeenexperimentallyprovedbyRanke（24/12。’DieBlutvertheilung，etc。derOrgane’1871asquotedbyJaeger’InSachenDarwin’s’1874page48。SeealsoH。Spencer’ThePrinciplesofBiology’
volume21866chapters3—5。）thattheflowofbloodisgreatlyincreasedtowardsanypartwhichisperformingwork，andsinksagainwhenthepartisatrest。Consequently，iftheworkisfrequent，thevesselsincreaseinsizeandthepartisbetternourished。Paget（24/13。’LecturesonPathology’1853
volume1page71。）alsoaccountsforthelong，thick，dark—colouredhairswhichoccasionallygrow，eveninyoungchildren，nearold—standinginflamedsurfacesorfracturedbonesbyanincreasedflowofbloodtothepart。WhenHunterinsertedthespurofacockintothecomb，whichiswellsuppliedwithblood—vessels，itgrewinonecasespirallytoalengthofsixinches，andinanothercaseforward，likeahorn，sothatthebirdcouldnottouchthegroundwithitsbeak。AccordingtotheinterestingobservationsofM。Sedillot（24/14。’ComptesRendus’September26，1864page539。），whenaportionofoneofthebonesofthelegofananimalisremoved，theassociatedboneenlargestillitattainsabulkequaltothatofthetwobones，ofwhichithastoperformthefunctions。Thisisbestexhibitedindogsinwhichthetibiahasbeenremoved;thecompanionbone，whichisnaturallyalmostfiliformandnotone—fifththesizeoftheother，soonacquiresasizeequaltoorgreaterthanthatofthetibia。Now，itisatfirstdifficulttobelievethatincreasedweightactingonastraightbonecould，byalternatelyincreasinganddiminishingthepressure，causethebloodtoflowmorefreelyinthevesselswhichpermeatetheperiosteumandthussupplymorenutrimenttothebone。
NeverthelesstheobservationsadducedbyMr。Spencer（24/15。H。Spencer’ThePrinciplesofBiology’volume2page243。），onthestrengtheningofthebowedbonesofricketychildren，alongtheirconcavesides，leadstothebeliefthatthisispossible。
Therockingofthestemofatreeincreasesinamarkedmannerthegrowthofthewoodytissueinthepartswhicharestrained。Prof。Sachsbelieves，fromreasonswhichheassigns，thatthisisduetothepressureofthebarkbeingrelaxedinsuchparts，andnotasKnightandH。Spencermaintain，toanincreasedflowofsapcausedbythemovementofthetrunk。（24/16。Ibidvolume2page269。Sachs’Text—bookofBotany’1875page734。）Buthardwoodytissuemaybedevelopedwithouttheaidofanymovement，asweseewithivycloselyattachedtoanoldwall。Inallsuchcases，itisverydifficulttodistinguishbetweentheeffectsoflong—continuedselectionandthosewhichfollowfromtheincreasedactionofthepart，ordirectlyfromsomeothercause。Mr。H。Spencer（24/17。Ibidvolume2page273。）acknowledgesthisdifficulty，andgivesasaninstancethethornsontreesandtheshellsofnuts。Herewehaveextremelyhardwoodytissuewithoutthepossibilityofanymovement，andwithout，asfaraswecansee，anyotherdirectlyexcitingcause;andasthehardnessofthesepartsisofmanifestservicetotheplant，wemaylookattheresultasprobablyduetotheselectionofso—calledspontaneousvariations。Everyoneknowsthathardworkthickenstheepidermisonthehands;andwhenwehearthatwithinfants，longbeforebirth，theepidermisisthickeronthepalmsandsolesofthefeetthanonanyotherpartofthebody，aswasobservedwithadmirationbyAlbinus（24/18。Paget’LecturesonPathology’volume2page209。），wearenaturallyinclinedtoattributethistotheinheritedeffectsoflong—continueduseorpressure。Wearetemptedtoextendthesamevieweventothehoofsofquadrupeds;butwhowillpretendtodeterminehowfarnaturalselectionmayhaveaidedintheformationofstructuresofsuchobviousimportancetotheanimal？
[Thatusestrengthensthemusclesmaybeseeninthelimbsofartisanswhofollowdifferenttrades;andwhenamuscleisstrengthened，thetendons，andthecrestsofbonetowhichtheyareattached，becomeenlarged;andthismustlikewisebethecasewiththeblood—vesselsandnerves。Ontheotherhand，whenalimbisnotused，asbyEasternfanatics，orwhenthenervesupplyingitwithnervouspoweriseffectuallydestroyed，themuscleswither。Soagain，whentheeyeisdestroyedtheopticnervebecomesatrophied，sometimeseveninthecourseofafewmonths。（24/19。Muller’Phys。’Englishtranslationpages54，791。Prof。Reedhasgiven（’PhysiologicalandAnat。Researches’page10）acuriousaccountoftheatrophyofthelimbsofrabbitsafterthedestructionofthenerve。）TheProteusisfurnishedwithbranchiaeaswellaswithlungs:
andSchreibers（24/20。QuotedbyLecoqin’Geograph。Bot。’tome11854page182。）foundthatwhentheanimalwascompelledtoliveindeepwater，thebranchiaeweredevelopedtothricetheirordinarysize，andthelungswerepartiallyatrophied。When，ontheotherhand，theanimalwascompelledtoliveinshallowwater，thelungsbecamelargerandmorevascular，whilstthebranchiaedisappearedinamoreorlesscompletedegree。Suchmodificationsastheseare，however，ofcomparativelylittlevalueforus，aswedonotactuallyknowthattheytendtobeinherited。
Inmanycasesthereisreasontobelievethatthelesseneduseofvariousorganshasaffectedthecorrespondingpartsintheoffspring。Butthereisnogoodevidencethatthiseverfollowsinthecourseofasinglegeneration。Itappears，asinthecaseofgeneralorindefinitevariability，thatseveralgenerationsmustbesubjectedtochangedhabitsforanyappreciableresult。
Ourdomesticfowls，ducks，andgeesehavealmostlost，notonlyintheindividualbutintherace，theirpowerofflight;forwedonotseeayoungfowl，whenfrightened，takeflightlikeayoungpheasant。HenceIwasledcarefullytocomparethelimb—bonesoffowls，ducks，pigeons，andrabbits，withthesamebonesinthewildparent—species。AsthemeasurementsandweightswerefullygivenintheearlierchaptersIneedhereonlyrecapitulatetheresults。Withdomesticpigeons，thelengthofthesternum，theprominenceofitscrest，thelengthofthescapulaeandfurculum，thelengthofthewingsasmeasuredfromtiptotipoftheradii，areallreducedrelativelytothesamepartsinthewildpigeon。Thewingandtailfeathers，however，areincreasedinlength，butthismayhaveaslittleconnectionwiththeuseofthewingsortail，asthelengthenedhaironadogwiththeamountofexercisewhichithashabituallytaken。Thefeetofpigeons，exceptinthelong—beakedraces，arereducedinsize。Withfowlsthecrestofthesternumislessprominent，andisoftendistortedormonstrous;thewing—boneshavebecomelighterrelativelytotheleg—bones，andareapparentlyalittleshorterincomparisonwiththoseoftheparent—form，theGallusbankiva。Withducks，thecrestofthesternumisaffectedinthesamemannerasintheforegoingcases:
thefurculum，coracoids，andscapulaeareallreducedinweightrelativelytothewholeskeleton:thebonesofthewingsareshorterandlighter，andthebonesofthelegslongerandheavier，relativelytoeachother，andrelativelytothewholeskeleton，incomparisonwiththesamebonesinthewild—duck。Thedecreasedweightandsizeofthebones，intheforegoingcases，isprobablytheindirectresultofthereactionoftheweakenedmusclesonthebones。I
failedtocomparethefeathersofthewingsofthetameandwildduck;butGloger（24/21。’DasAbandernderVogel’1833s。74。）assertsthatinthewildduckthetipsofthewing—feathersreachalmosttotheendofthetail，whilstinthedomesticducktheyoftenhardlyreachtoitsbase。Heremarksalsoonthegreaterthicknessofthelegs，andsaysthattheswimmingmembranebetweenthetoesisreduced;butIwasnotabletodetectthislatterdifference。
Withthedomesticatedrabbitthebody，togetherwiththewholeskeleton，isgenerallylargerandheavierthaninthewildanimal，andtheleg—bonesareheavierindueproportion;butwhateverstandardofcomparisonbetaken，neithertheleg—bonesnorthescapulaehaveincreasedinlengthproportionallywiththeincreaseddimensionsoftherestoftheskeleton。Theskullhasbecomeinamarkedmannernarrower，and，fromthemeasurementsofitscapacityformerlygiven，wemayconclude，thatthisnarrownessresultsfromthedecreasedsizeofthebrain，consequentonthementallyinactivelifeledbytheseclosely—confinedanimals。
Wehaveseenintheeighthchapterthatsilk—moths，whichhavebeenkeptduringmanycenturiescloselyconfined，emergefromtheircocoonswiththeirwingsdistorted，incapableofflight，oftengreatlyreducedinsize，oreven，accordingtoQuatrefages，quiterudimentary。ThisconditionofthewingsmaybelargelyowingtothesamekindofmonstrositywhichoftenaffectswildLepidopterawhenartificiallyrearedfromthecocoon;oritmaybeinpartduetoaninherenttendency，whichiscommontothefemalesofmanyBombycidae，tohavetheirwingsinamoreorlessrudimentarystate;butpartoftheeffectmaybeattributedtolong—continueddisuse。]
Fromtheforegoingfactstherecanbenodoubtthatwithourancientlydomesticatedanimals，certainboneshaveincreasedordecreasedinsizeandweightowingtoincreasedordecreaseduse;buttheyhavenotbeenmodified，asshownintheearlierchapters，inshapeorstructure。Withanimalslivingafreelifeandoccasionallyexposedtoseverecompetitionthereductionwouldtendtobegreater，asitwouldbeanadvantagetothemtohavethedevelopmentofeverysuperfluouspartsaved。Withhighly—feddomesticatedanimals，ontheotherhand，thereseemstobenoeconomyofgrowth，noranytendencytotheeliminationofsuperfluousdetails。ButtothissubjectI
shallrecur。
Turningnowtomoregeneralobservations，Nathusiushasshownthatwiththeimprovedracesofthepig，theshortenedlegsandsnout，theformofthearticularcondylesoftheocciput，andthepositionofthejawswiththeuppercanineteethprojectinginamostanomalousmannerinfrontofthelowercanines，maybeattributedtothesepartsnothavingbeenfullyexercised。Forthehighly—cultivatedracesdonottravelinsearchoffood，norrootupthegroundwiththeirringedmuzzles。（24/22。Nathusius’DieRacendesSchweines’
1860s。53，57;’Vorstudien……Schweineschadel’1864s。103，130，133。Prof。
LucaesupportsandextendstheconclusionsofVonNathusius:’DerSchadeldesMaskenschweines’1870。）Thesemodificationsofstructure，whichareallstrictlyinherited，characteriseseveralimprovedbreeds，sothattheycannothavebeenderivedfromanysingledomesticstock。Withrespecttocattle，ProfessorTannerhasremarkedthatthelungsandliverintheimprovedbreeds\"arefoundtobeconsiderablyreducedinsizewhencomparedwiththosepossessedbyanimalshavingperfectliberty\"（24/23。’JournalofAgricultureofHighlandSoc。’July1860page321。）;andthereductionoftheseorgansaffectsthegeneralshapeofthebody。Thecauseofthereducedlungsinhighly—bredanimalswhichtakelittleexerciseisobvious;andperhapsthelivermaybeaffectedbythenutritiousandartificialfoodonwhichtheylargelysubsist。Again，Dr。Wilckensasserts（24/24。’Landwirth。Wochenblatt’
No。10。）thatvariouspartsofthebodycertainlydifferinAlpineandlowlandbreedsofseveraldomesticatedanimals，owingtotheirdifferenthabitsoflife;forinstance，theneckandfore—legsinlength，andthehoofsinshape。
[Itiswellknownthat，whenanarteryistied，theanastomosingbranches，frombeingforcedtotransmitmoreblood，increaseindiameter;andthisincreasecannotbeaccountedforbymereextension，astheircoatsgaininstrength。Withrespecttoglands，SirJ。Pagetobservesthat\"whenonekidneyisdestroyedtheotheroftenbecomesmuchlarger，anddoesdoublework。\"
（24/25。’LecturesonSurgicalPathology’1853volume1page27。）Ifwecomparethesizeoftheuddersandtheirpowerofsecretionincowswhichhavebeenlongdomesticated，andincertainbreedsofthegoatinwhichtheuddersnearlytouchtheground，withtheseorgansinwildorhalf—domesticatedanimals，thedifferenceisgreat。Agoodcowwithusdailyyieldsmorethanfivegallons，orfortypintsofmilk，whilstafirst—rateanimal，kept，forinstance，bytheDamarasofSouthAfrica（24/26。Andersson’TravelsinSouthAfrica’page318。ForanalogouscasesinSouthAmericaseeAug。St。—Hilaire’VoyagedanslaProvincedeGoyaz’tome1page71。），\"rarelygivesmorethantwoorthreepintsofmilkdaily，and，shouldhercalfbetakenfromher，sheabsolutelyrefusestogiveany。\"Wemayattributetheexcellenceofourcowsandofcertaingoats，partlytothecontinuedselectionofthebestmilkinganimals，andpartlytotheinheritedeffectsoftheincreasedaction，throughman’sart，ofthesecretingglands。
Itisnotoriousthatshort—sightisinherited;andwehaveseeninthetwelfthchapterfromthestatisticalresearchesofM。Giraud—Teulon，thatthehabitofviewingnearobjectsgivesatendencytoshort—sight。Veterinariansareunanimousthathorsesareaffectedwithspavins，splints，ringbones，etc。，frombeingshodandfromtravellingonhardroads，andtheyarealmostequallyunanimousthatatendencytothesemalformationsistransmitted。FormerlyhorseswerenotshodinNorthCarolina，andithasbeenassertedthattheydidnotthensufferfromthesediseasesofthelegsandfeet。（24/27。Brickell’Nat。Hist。ofNorthCarolina’1739page53。）]
Ourdomesticatedquadrupedsarealldescended，asfarasisknown，fromspecieshavingerectears;yetfewkindscanbenamed，ofwhichatleastoneracehasnotdroopingears。CatsinChina，horsesinpartsofRussia，sheepinItalyandelsewhere，theguinea—pigformerlyinGermany，goatsandcattleinIndia，rabbits，pigs，anddogsinalllong—civilisedcountrieshavedependentears。Withwildanimals，whichconstantlyusetheirearslikefunnelstocatcheverypassingsound，andespeciallytoascertainthedirectionwhenceitcomes，thereisnot，asMr。Blythhasremarked，anyspecieswithdroopingearsexcepttheelephant。Hencetheincapacitytoerecttheearsiscertainlyinsomemannertheresultofdomestication;andthisincapacityhasbeenattributedbyvariousauthors（24/28。LivingstonequotedbyYouatton’Sheep’
page142。Hodgsonin’JournalofAsiaticSoc。ofBengal’volume161847page1006etc。etc。OntheotherhandDr。Wilckensarguesstronglyagainstthebeliefthatthedroopingoftheearsistheresultofdisuse:’JahrbuchderdeutschenViehzucht’1866。）todisuse，foranimalsprotectedbymanarenotcompelledhabituallytousetheirears。Col。HamiltonSmith（24/29。
’Naturalist’sLibrary’Dogsvolume21840page104。）statesthatinancienteffigiesofthedog，\"withtheexceptionofoneEgyptianinstance，nosculptureoftheearlierGrecianeraproducesrepresentationsofhoundswithcompletelydroopingears;thosewiththemhalfpendulousaremissinginthemostancient;andthischaracterincreases，bydegrees，intheworksoftheRomanperiod。\"Godronalsohasremarked\"thatthepigsoftheancientEgyptianshadnottheirearsenlargedandpendent。\"（24/30。’Del’Espece’tome11859page367。）Butitisremarkablethatthedroopingoftheearisnotaccompaniedbyanydecreaseinsize;onthecontrary，animalssodifferentasfancyrabbits，certainIndianbreedsofthegoat，ourpettedspaniels，blood—
hounds，andotherdogs，haveenormouslyelongatedears，sothatitwouldappearasiftheirweighthadcausedthemtodroop，aidedperhapsbydisuse。
Withrabbits，thedroopingofthemuchelongatedearshasaffectedeventhestructureoftheskull。
Thetailofnowildanimal，asremarkedtomebyMr。Blyth，iscurled;whereaspigsandsomeracesofdogshavetheirtailsmuchcurled。Thisdeformity，therefore，appearstobetheresultofdomestication，butwhetherinanywayconnectedwiththelesseneduseofthetailisdoubtful。
Theepidermisonourhandsiseasilythickened，aseveryoneknows，byhardwork。InadistrictofCeylonthesheephave\"hornycallositiesthatdefendtheirknees，andwhicharisefromtheirhabitofkneelingdowntocroptheshortherbage，andthisdistinguishestheJaffnaflocksfromthoseofotherportionsoftheisland;\"butitisnotstatedwhetherthispeculiarityisinherited。（24/31。’Ceylon’bySirJ。E。Tennent1859volume2page531。）
Themucousmembranewhichlinesthestomachiscontinuouswiththeexternalskinofthebody;thereforeitisnotsurprisingthatitstextureshouldbeaffectedbythenatureofthefoodconsumed，butotherandmoreinterestingchangeslikewisefollow。Hunterlongagoobservedthatthemuscularcoatofthestomachofagull（Larustridactylus）whichhadbeenfedforayearchieflyongrainwasthickened;and，accordingtoDr。Edmondston，asimilarchangeperiodicallyoccursintheShetlandIslandsinthestomachoftheLarusargentatus，whichinthespringfrequentsthecornfieldsandfeedsontheseed。Thesamecarefulobserverhasnoticedagreatchangeinthestomachofaravenwhichhadbeenlongfedonvegetablefood。Inthecaseofanowl（Strixgrallaria），similarlytreated，Menetriesstatesthattheformofthestomachwaschanged，theinnercoatbecameleathery，andtheliverincreasedinsize。
Whetherthesemodificationsinthedigestiveorganswouldinthecourseofgenerationsbecomeinheritedisnotknown。（24/32。FortheforegoingstatementsseeHunter’EssaysandObservations’1861volume2page329;Dr。
Edmondston，asquotedinMacgillivray’BritishBirds’volume5page550:
MenetriesasquotedinBronn’GeschichtederNatur’b。2s。110。）
Theincreasedordiminishedlengthoftheintestines，whichapparentlyresultsfromchangeddiet，isamoreremarkablecase，becauseitischaracteristicofcertainanimalsintheirdomesticatedcondition，andthereforemustbeinherited。Thecomplexabsorbentsystem，theblood—vessels，nerves，andmuscles，arenecessarilyallmodifiedtogetherwiththeintestines。AccordingtoDaubenton，theintestinesofthedomesticcatareone—thirdlongerthanthoseofthewildcatofEurope;andalthoughthisspeciesisnottheparent—
stockofthedomesticanimal，yet，asIsidoreGeoffroyhasremarked，theseveralspeciesofcatsaresocloselyalliedthatthecomparisonisprobablyafairone。Theincreasedlengthappearstobeduetothedomesticcatbeinglessstrictlycarnivorousinitsdietthananywildfelinespecies;forinstance，IhaveseenaFrenchkitteneatingvegetablesasreadilyasmeat。
AccordingtoCuvier，theintestinesofthedomesticatedpigexceedgreatlyinproportionatelengththoseofthewildboar。Inthetameandwildrabbitthechangeisofanoppositenature，andprobablyresultsfromthenutritiousfoodgiventothetamerabbit。（24/33。ThesestatementsontheintestinesaretakenfromIsidoreGeoffroySaint—Hilaire’Hist。Nat。Gen。’tome3pages427，441。）
CHANGEDANDINHERITEDHABITSOFLIFE。
Thissubject，asfarasthementalpowersofanimalsareconcerned，soblendsintoinstinct，thatIwillhereonlyremindthereaderofsuchcasesasthetamenessofourdomesticatedanimals——thepointingorretrievingofdogs——
theirnotattackingthesmalleranimalskeptbyman——andsoforth。Howmuchofthesechangesoughttobeattributedtomerehabit，andhowmuchtotheselectionofindividualswhichhavevariedinthedesiredmanner，irrespectivelyofthespecialcircumstancesunderwhichtheyhavebeenkept，canseldombetold。
Wehavealreadyseenthatanimalsmaybehabituatedtoachangeddiet;butsomeadditionalinstancesmaybegiven。InthePolynesianIslandsandinChinathedogisfedexclusivelyonvegetablematter，andthetasteforthiskindoffoodistoacertainextentinherited。（24/34。GilbertWhite’Nat。Hist。
Selborne’1825volume2page121。）Oursportingdogswillnottouchthebonesofgamebirds，whilstmostotherdogsdevourthemwithgreediness。Insomepartsoftheworldsheephavebeenlargelyfedonfish。Thedomestichogisfondofbarley，thewildboarissaidtodisdainit;andthedisdainispartiallyinherited，forsomeyoungwildpigsbredincaptivityshowedanaversionforthisgrain，whilstothersofthesamebroodrelishedit。（24/35。
Burdach’TraitedePhys。’tome2page267asquotedbyDr。P。Lucas’L’Hered。
Nat。’tome1page388。）OneofmyrelationsbredsomeyoungpigsfromaChinesesowbyawildAlpineboar;theylivedfreeinthepark，andweresotamethattheycametothehousetobefed;buttheywouldnottouchswill，whichwasdevouredbytheotherpigs。Ananimalwhenonceaccustomedtoanunnaturaldiet，whichcangenerallybeeffectedonlyduringyouth，dislikesitsproperfood，asSpallanzanifoundtobethecasewithapigeonwhichhadbeenlongfedonmeat。Individualsofthesamespeciestaketonewfoodwithdifferentdegreesofreadiness;onehorse，itisstated，soonlearnedtoeatmeat，whilstanotherwouldhaveperishedfromhungerratherthanhavepartakenofit。（24/36。ThisandseveralothercasesaregivenbyColin’PhysiologieComp。desAnimauxDom。’1854tome1page426。）ThecaterpillarsoftheBombyxhesperusfeedinastateofnatureontheleavesoftheCafediable，but，afterhavingbeenrearedontheAilanthus，theywouldnottouchtheCafediable，andactuallydiedofhunger。（24/37。M。MichelydeCayennein’Bull。
Soc。d’Acclimat。’tome81861page563。）
Ithasbeenfoundpossibletoaccustommarinefishtoliveinfreshwater;butassuchchangesinfishandothermarineanimalshavebeenchieflyobservedinastateofnature，theydonotproperlybelongtoourpresentsubject。Theperiodofgestationandofmaturity，asshownintheearlierchapters，——theseasonandthefrequencyoftheactofbreeding，——haveallbeengreatlymodifiedunderdomestication。WiththeEgyptiangoosetherateofchangewithrespecttotheseasonhasbeenrecorded。（24/38。Quatrefages’Unitedel’EspeceHumaine’1861page79。）Thewilddrakepairswithonefemale，thedomesticdrakeispolygamous。Certainbreedsoffowlshavelostthehabitofincubation。Thepacesofthehorse，andthemannerofflightofcertainbreedsofthepigeon，havebeenmodifiedandareinherited。Cattle，horses，andpigshavelearnttobrowseunderwaterintheSt。John’sRiver，EastFlorida，wheretheVallisneriahasbeenlargelynaturalised。ThecowswereobservedbyProf。
Wymantokeeptheirheadsimmersedfor\"aperiodvaryingfromfifteentothirty—fiveseconds。\"（24/39。’TheAmericanNaturalist’April1874page237。）
Thevoicediffersmuchincertainkindsoffowlsandpigeons。Somevarietiesareclamorousandotherssilent，astheCallandcommonduck，ortheSpitzandpointerdog。Everyoneknowshowthebreedsofthedogdifferfromoneanotherintheirmannerofhunting，andintheirardourafterdifferentkindsofgameorvermin。
Withplantstheperiodofvegetationiseasilychangedandisinherited，asinthecaseofsummerandwinterwheat，barley，andvetches;buttothissubjectweshallimmediatelyreturnunderacclimatisation。Annualplantssometimesbecomeperennialunderanewclimate，asIhearfromDr。HookeristhecasewiththestockandmignonetteinTasmania。Ontheotherhand，perennialssometimesbecomeannuals，aswiththeRicinusinEngland，andas，accordingtoCaptainMangles，withmanyvarietiesoftheheartsease。VonBerg（24/40。
’Flora’1835b。2page504。）raisedfromseedofVerbascumphoeniceum，whichisusuallyabiennial，bothannualandperennialvarieties。Somedeciduousbushesbecomeevergreeninhotcountries。（24/41。Alph。deCandolle’Geograph。
Bot。’tome2page1078。）Ricerequiresmuchwater，butthereisonevarietyinIndiawhichcanbegrownwithoutirrigation。（24/42。Royle’IllustrationsoftheBotanyoftheHimalaya’page19。）Certainvarietiesoftheoatandofourothercerealsarebestfittedforcertainsoils。（24/43。’Gardener’sChronicle’1850pages204，219。）Endlesssimilarfactscouldbegivenintheanimalandvegetablekingdoms。Theyarenoticedherebecausetheyillustrateanalogousdifferencesincloselyalliednaturalspecies，andbecausesuchchangedhabitsoflife，whetherduetohabit，ortothedirectactionofexternalconditions，ortoso—calledspontaneousvariability，wouldbeapttoleadtomodificationsofstructure。
ACCLIMATISATION。
Fromthepreviousremarkswearenaturallyledtothemuchdisputedsubjectofacclimatisation。Therearetwodistinctquestions:Dovarietiesdescendedfromthesamespeciesdifferintheirpoweroflivingunderdifferentclimates？Andsecondly，iftheysodiffer，howhavetheybecomethusadapted？WehaveseenthatEuropeandogsdonotsucceedwellinIndia，anditisasserted（24/44。
Rev。R。Everest’JournalAs。Soc。ofBengal’volume3page19。），thatnoonehastheresucceededinkeepingtheNewfoundlandlongalive;butthenitmaybeargued，andprobablywithtruth，thatthesenorthernbreedsarespecificallydistinctfromthenativedogswhichflourishinIndia。Thesameremarkmaybemadewithrespecttodifferentbreedsofsheep，ofwhich，accordingtoYouatt（24/45。Youatton’Sheep’1838page491。），notonebrought\"fromatorridclimatelastsoutthesecondyear，\"intheZoologicalGardens。Butsheeparecapableofsomedegreeofacclimatisation，forMerinosheepbredattheCapeofGoodHopehavebeenfoundfarbetteradaptedforIndiathanthoseimportedfromEngland。（24/46。Royle’Prod。ResourcesofIndia’page153。）Itisalmostcertainthatallthebreedsofthefowlaredescendedfromonespecies;buttheSpanishbreed，whichthereisgoodreasontobelieveoriginatedneartheMediterranean（24/47。Tegetmeier’PoultryBook’1866page102。），thoughsofineandvigorousinEngland，suffersmorefromfrostthananyotherbreed。
TheArrindysilkmothintroducedfromBengal，andtheAilanthusmothfromthetemperateprovinceofShanTung，inChina，belongtothesamespecies，aswemayinferfromtheiridentityinthecaterpillar，cocoon，andmaturestates（24/48。Dr。R。PatersoninapapercommunicatedtoBot。Soc。ofCanadaquotedinthe’Reader’1863November13。）;yettheydiffermuchinconstitution:theIndianform\"willflourishonlyinwarmlatitudes，\"theotherisquitehardyandwithstandscoldandrain。
[Plantsaremorestrictlyadaptedtoclimatethanareanimals。Thelatterwhendomesticatedwithstandsuchgreatdiversitiesofclimate，thatwefindnearlythesamespeciesintropicalandtemperatecountries;whilstthecultivatedplantsarewidelydissimilar。Hencealargerfieldisopenforinquiryinregardtotheacclimatisationofplantsthanofanimals。Itisnoexaggerationtosaythatwithalmosteveryplantwhichhaslongbeencultivated，varietiesexistwhichareendowedwithconstitutionsfittedforverydifferentclimates;
Iwillselectonlyafewofthemorestrikingcases，asitwouldbetedioustogiveall。InNorthAmericanumerousfruit—treeshavebeenraised，andinhorticulturalpublications，——forinstance，inthatbyDowning，——listsaregivenofthevarietieswhicharebestabletowithstandthesevereclimateofthenorthernStatesandCanada。ManyAmericanvarietiesofthepear，plum，andpeachareexcellentintheirowncountry，butuntilrecently，hardlyonewasknownthatsucceededinEngland;andwithapples（24/49。SeeremarksbyEditorin’Gardener’sChronicle’1848page5。），notonesucceeds。ThoughtheAmericanvarietiescanwithstandasevererwinterthanours，thesummerhereisnothotenough。Fruit—treeshavealsooriginatedinEuropewithdifferentconstitutions，buttheyarenotmuchnoticed，becausenurserymenheredonotsupplywideareas。TheForellepearflowersearly，andwhentheflowershavejustset，andthisisthecriticalperiod，theyhavebeenobserved，bothinFranceandEngland，towithstandwithcompleteimpunityafrostof18degandeven14degFahr。，whichkilledtheflowers，whetherfullyexpandedorinbud，ofallotherkindsofpears。（24/50。’Gardener’sChronicle’1860page938。
RemarksbyEditorandquotationfromDecaisne。）Thispowerintheflowerofresistingcoldandafterwardsproducingfruitdoesnotinvariablydepend，asweknowongoodauthority（24/51。J。deJongheofBrusselsin’Gardener’sChronicle’1857page612。），ongeneralconstitutionalvigour。Inproceedingnorthward，thenumberofvarietieswhicharefoundcapableofresistingtheclimaterapidlydecreases，asmaybeseeninthelistofthevarietiesofthecherry，apple，andpear，whichcanbecultivatedintheneighbourhoodofStockholm。（24/52。Ch。Martius’VoyageBot。CotesSept。delaNorvege’page26。）NearMoscow，PrinceTroubetzkoyplantedforexperimentintheopengroundseveralvarietiesofthepear，butonealone，thePoiresansPepins，withstoodthecoldofwinter。（24/53。’Journaldel’Acad。Hort。deGand’quotedin’Gardener’sChronicle’1859page7。）Wethusseethatourfruit—trees，likedistinctspeciesofthesamegenus，certainlydifferfromeachotherintheirconstitutionaladaptationtodifferentclimates。