Ontheotherhand，withmaleanimals，itisnotoriousthatthesecondarysexualcharactersaremoreorlesscompletelylostwhentheyaresubjectedtocastration。Thus，iftheoperationbeperformedonayoungcock，henever，asYarrellstates，crowsagain;thecomb，wattles，andspursdonotgrowtotheirfullsize，andthehacklesassumeanintermediateappearancebetweentruehacklesandthefeathersofthehen。Casesarerecordedofconfinement，whichoftenaffectsthereproductivesystem，causinganalogousresults。Butcharactersproperlyconfinedtothefemalearelikewiseacquiredbythemale;
thecapontakestosittingoneggs，andwillbringupchickens;andwhatismorecurious，theutterlysterilemalehybridsfromthepheasantandthefowlactinthesamemanner，"theirdelightbeingtowatchwhenthehensleavetheirnests，andtotakeonthemselvestheofficeofasitter。"（13/57。
’CottageGardener’1860page379。）ThatadmirableobserverReaumur（13/58。
’ArtdefaireEclore’etc。1749tome2page8。）assertsthatacock，bybeinglongconfinedinsolitudeanddarkness，canbetaughttotakechargeofyoungchickens;hethenuttersapeculiarcry，andretainsduringhiswholelifethisnewlyacquiredmaternalinstinct。Themanywell—ascertainedcasesofvariousmalemammalsgivingmilkshowsthattheirrudimentarymammaryglandsretainthiscapacityinalatentcondition。
Wethusseethatinmany，probablyinallcases，thesecondarycharactersofeachsexliedormantorlatentintheoppositesex，readytobeevolvedunderpeculiarcircumstances。Wecanthusunderstandhow，forinstance，itispossibleforagoodmilkingcowtotransmithergoodqualitiesthroughhermaleoffspringtofuturegenerations;forwemayconfidentlybelievethatthesequalitiesarepresent，thoughlatent，inthemalesofeachgeneration。
Soitiswiththegame—cock，whocantransmithissuperiorityincourageandvigourthroughhisfemaletohismaleoffspring;andwithmanitisknown（13/59。SirH。Holland’MedicalNotesandReflections’3rdedition1855page31。）thatdiseases，suchashydrocele，necessarilyconfinedtothemalesex，canbetransmittedthroughthefemaletothegrandson。Suchcasesastheseoffer，aswasremarkedatthecommencementofthischapter，thesimplestpossibleexamplesofreversion;andtheyareintelligibleonthebeliefthatcharacterscommontothegrandparentandgrandchildofthesamesexarepresent，thoughlatent，intheintermediateparentoftheoppositesex。
Thesubjectoflatentcharactersissoimportant，asweshallseeinafuturechapter，thatIwillgiveanotherillustration。Manyanimalshavetherightandleftsidesoftheirbodyunequallydeveloped:thisiswellknowntobethecasewithflat—fish，inwhichtheonesidediffersinthicknessandcolourandintheshapeofthefins，fromtheother，andduringthegrowthoftheyoungfishoneeyeisgraduallytwistedfromthelowertotheuppersurface。（13/60。
SeeSteenstruponthe’ObliquityofFlounders’inAnnalsandMag。ofNat。
Hist。’May1865page361。IhavegivenanabstractofMalm’sexplanationofthiswonderfulphenomenoninthe’OriginofSpecies’6thEditionpage186。）Inmostflat—fishestheleftistheblindside，butinsomeitistheright;
thoughinbothcasesreversedor"wrongfishes，"areoccasionallydeveloped;
andinPlatessaflesustherightorleftsideisindifferentlytheupperone。
Withgasteropodsorshell—fish，therightandleftsidesareextremelyunlike;
thefargreaternumberofspeciesaredextral，withrareandoccasionalreversalsofdevelopment;andsomefewarenormallysinistral;butcertainspeciesofBulimus，andmanyAchatinellae（13/61。Dr。E。vonMartensin’AnnalsandMag。ofNat。Hist。’March1866page209。）areasoftensinistralasdextral。Iwillgiveananalogouscaseinthegreatarticulatekingdom:thetwosidesofVerruca（13/62。Darwin’Balanidae’RaySoc。1854page499:seealsotheappendedremarksontheapparentlycapriciousdevelopmentofthethoraciclimbsontherightandleftsidesinthehighercrustaceans。）aresowonderfullyunlike，thatwithoutcarefuldissectionitisextremelydifficulttorecognisethecorrespondingpartsontheoppositesidesofthebody;yetitisapparentlyamerematterofchancewhetheritbetherightortheleftsidethatundergoessosingularamountofchange。Oneplantisknowntome（13/63。
Mormodesignea:Darwin’FertilisationofOrchids’1862page251。）inwhichtheflower，accordingasitstandsontheoneorothersideofthespike，isunequallydeveloped。Inalltheforegoingcasesthetwosidesareperfectlysymmetricalatanearlyperiodofgrowth。Now，wheneveraspeciesisasliabletobeunequallydevelopedontheoneasontheotherside，wemayinferthatthecapacityforsuchdevelopmentispresent，thoughlatent，intheundevelopedside。Andasareversalofdevelopmentoccasionallyoccursinanimalsofmanykinds，thislatentcapacityisprobablyverycommon。
Thebestyetsimplestcasesofcharacterslyingdormantare，perhaps，thosepreviouslygiven，inwhichchickensandyoungpigeons，raisedfromacrossbetweendifferentlycolouredbirds，areatfirstofonecolour，butinayearortwoacquirefeathersofthecolouroftheotherparent;forinthiscasethetendencytoachangeofplumageisclearlylatentintheyoungbird。Soitiswithhornlessbreedsofcattle，someofwhichacquiresmallhornsastheygrowold。Purelybredblackandwhitebantams，andsomeotherfowls，occasionallyassume，withadvancingyears，theredfeathersoftheparent—
species。Iwillhereaddasomewhatdifferentcase，asitconnectsinastrikingmannerlatentcharactersoftwoclasses。Mr。Hewitt（13/64。’JournalofHorticulture’July1864page38。IhavehadtheopportunityofexaminingtheseremarkablefeathersthroughthekindnessofMr。Tegetmeier。）possessedanexcellentSebrightgold—lacedbantamhen，which，asshebecameold，grewdiseasedinherovaria，andassumedmalecharacters。Inthisbreedthemalesresemblethefemalesinallrespectsexceptintheircombs，wattles，spurs，andinstincts;henceitmighthavebeenexpectedthatthediseasedhenwouldhaveassumedonlythosemasculinecharacterswhicharepropertothebreed，butsheacquired，inaddition，well—archedtailsickle—feathersquiteafootinlength，saddle—feathersontheloins，andhacklesontheneck，——ornamentswhich，asMr。Hewittremarks，"wouldbeheldasabominableinthisbreed。"TheSebrightbantamisknown（13/65。’ThePoultryBook’byMr。Tegetmeier1866
page241。）tohaveoriginatedabouttheyear1800fromacrossbetweenacommonbantamandaPolishfowl，recrossedbyahen—tailedbantam，andcarefullyselected;hencetherecanhardlybeadoubtthatthesickle—feathersandhackleswhichappearedintheoldhenwerederivedfromthePolishfowlorcommonbantam;andwethusseethatnotonlycertainmasculinecharacterspropertotheSebrightbantam，butothermasculinecharactersderivedfromthefirstprogenitorsofthebreed，removedbyaperiodofabovesixtyyears，werelyinglatentinthishenbird，readytobeevolvedassoonasherovariabecamediseased。
Fromtheseseveralfactsitmustbeadmittedthatcertaincharacters，capacities，andinstincts，maylielatentinanindividual，andeveninasuccessionofindividuals，withoutourbeingabletodetecttheleastsignoftheirpresence。Whenfowls，pigeons，orcattleofdifferentcoloursarecrossed，andtheiroffspringchangecolourastheygrowold，orwhenthecrossedturbitacquiredthecharacteristicfrillafteritsthirdmoult，orwhenrarely—bredbantamspartiallyassumetheredplumageoftheirprototype，wecannotdoubtthatthesequalitieswerefromthefirstpresent，thoughlatent，intheindividualanimal，likethecharactersofamothinthecaterpillar。Now，iftheseanimalshadproducedoffspringbeforetheyhadacquiredwithadvancingagetheirnewcharacters，nothingismoreprobablethanthattheywouldhavetransmittedthemtosomeoftheiroffspring，whointhiscasewouldinappearancehavereceivedsuchcharactersfromtheirgrand—
parentsormoredistantprogenitors。Weshouldthenhavehadacaseofreversion，thatis，ofthereappearanceinthechildofanancestralcharacter，actuallypresent，thoughduringyouthcompletelylatent，intheparent;andthiswemaysafelyconcludeiswhatoccursinallreversionstoprogenitors，howeverremote。
Thisviewofthelatencyineachgenerationofallthecharacterswhichappearthroughreversion，isalsosupportedbytheiractualpresenceinsomecasesduringearlyyouthalone，orbytheirmorefrequentappearanceandgreaterdistinctnessatthisagethanduringmaturity。Wehaveseenthatthisisoftenthecasewiththestripesonthelegsandfacesoftheseveralspeciesofthehorsegenus。TheHimalayanrabbit，whencrossed，sometimesproducesoffspringwhichreverttotheparentsilver—greybreed，andwehaveseenthatinpurelybredanimalspale—greyfuroccasionallyreappearsduringearlyyouth。Blackcats，wemayfeelassured，wouldoccasionallyproducebyreversiontabbies;
andonyoungblackkittens，withapedigree（13/66。CarlVogt’LecturesonMan’Englishtranslation1864page411。）knowntohavebeenlongpure，fainttracesofstripesmayalmostalwaysbeseenwhichafterwardsdisappear。
HornlessSuffolkcattleoccasionallyproducebyreversionhornedanimals;andYouatt（13/67。’OnCattle’page174。）assertsthateveninhornlessindividuals"therudimentofahornmaybeoftenfeltatanearlyage。"
Nodoubtitappearsatfirstsightinthehighestdegreeimprobablethatineveryhorseofeverygenerationthereshouldbealatentcapacityandtendencytoproducestripes，thoughthesemaynotappearonceinathousandgenerations;thatineverywhite，black，orothercolouredpigeon，whichmayhavetransmitteditspropercolourduringcenturies，thereshouldbealatentcapacityintheplumagetobecomeblueandtobemarkedwithcertaincharacteristicbars;thatineverychildinasix—fingeredfamilythereshouldbethecapacityfortheproductionofanadditionaldigit;andsoinothercases。Nevertheless，thereisnomoreinherentimprobabilityinthisbeingthecasethaninauselessandrudimentaryorgan，oreveninonlyatendencytotheproductionofarudimentaryorgan，beinginheritedduringmillionsofgenerations，asiswellknowntooccurwithamultitudeoforganicbeings。
Thereisnomoreinherentimprobabilityineachdomesticpig，duringathousandgenerations，retainingthecapacityandtendencytodevelopgreattusksunderfittingconditions，thanintheyoungcalfhavingretained，foranindefinitenumberofgenerationsrudimentaryincisorteeth，whichneverprotrudethroughthegums。
Ishallgiveattheendofthenextchapterasummaryofthethreeprecedingchapters;butasisolatedandstrikingcasesofreversionhaveherebeenchieflyinsistedon，Iwishtoguardthereaderagainstsupposingthatreversionisduetosomerareoraccidentalcombinationofcircumstances。Whenacharacter，lostduringhundredsofgenerations，suddenlyreappears，nodoubtsomesuchcombinationmustoccur;butreversions，totheimmediatelyprecedinggenerationsmaybeconstantlyobserved，atleast，intheoffspringofmostunions。Thishasbeenuniversallyrecognisedinthecaseofhybridsandmongrels，butithasbeenrecognisedsimplyfromthedifferencebetweentheunitedformsrenderingtheresemblanceoftheoffspringtotheirgrandparentsormoreremoteprogenitorsofeasydetection。Reversionislikewisealmostinvariablytherule，asMr。Sedgwickhasshown，withcertaindiseases。Hencewemustconcludethatatendencytothispeculiarformoftransmissionisanintegralpartofthegenerallawofinheritance。
MONSTROSITIES。
Alargenumberofmonstrousgrowthsandoflesseranomaliesareadmittedbyeveryonetobeduetoanarrestofdevelopment，thatis，tothepersistenceofanembryoniccondition。Butmanymonstrositiescannotbethusexplained;
forpartsofwhichnotracecanbedetectedintheembryo，butwhichoccurinothermembersofthesameclassofanimalsoccasionallyappear，andthesemayprobablywithtruthbeattributedtoreversion。As，however，IhavetreatedthissubjectasfullyasIcouldinmy’DescentofMan’（ch。12ndedition），I
willnothererecurtoit。
[Whenflowerswhichhavenormallyanirregularstructurebecomeregularorpeloric，thechangeisgenerallylookedatbybotanistsasareturntotheprimitivestate。ButDr。MaxwellMasters（13/68。’NaturalHist。Review’April1863page258。SeealsohisLecture，RoyalInstitution，March16，1860。OnsamesubjectseeMoquin—Tandon’ElementsdeTeratologie’1841pages184，352。
Dr。Peyritschhascollectedalargenumberofveryinterestingcases’Sitzb。
d。k。Akad。d。Wissensch。’Wienb。60andespeciallyb。661872page125。），whohasablydiscussedthissubject，remarksthatwhen，forinstance，allthesepalsofaTropaeolumbecomegreenandofthesameshape，insteadofbeingcolouredwithoneprolongedintoaspur，orwhenallthepetalsofaLinariabecomesimpleandregular，suchcasesmaybeduemerelytoanarrestofdevelopment;forintheseflowersalltheorgansduringtheirearliestconditionaresymmetrical，and，ifarrestedatthisstageofgrowth，theywouldnotbecomeirregular。If，moreover，thearrestweretotakeplaceatastillearlierperiodofdevelopment，theresultwouldbeasimpletuftofgreenleaves;andnooneprobablywouldcallthisacaseofreversion。Dr。
Mastersdesignatesthecasesfirstalludedtoasregularpeloria;andothers，inwhichallthecorrespondingpartsassumeasimilarformofirregularity，aswhenallthepetalsinaLinariabecomespurred，asirregularpeloria。Wehavenorighttoattributetheselattercasestoreversion，untilitcanbeshownthattheparent—form，forinstance，ofthegenusLinariahadhadallitspetalsspurred;forachanceofthisnaturemightresultfromthespreadingofananomalousstructure，inaccordancewiththelaw，tobediscussedinafuturechapter，ofhomologouspartstendingtovaryinthesamemanner。ButasbothformsofpeloriafrequentlyoccuronthesameindividualplantoftheLinaria（13/69。Verlot’DesVarietes’1865page89;Naudin’NouvellesArchivesduMuseum’tome1page137。），theyprobablystandinsomecloserelationtooneanother。Onthedoctrinethatpeloriaissimplytheresultofanarrestofdevelopment，itisdifficulttounderstandhowanorganarrestedataveryearlyperiodofgrowthshouldacquireitsfullfunctionalperfection;——howapetal，supposedtobethusarrested，shouldacquireitsbrilliantcolours，andserveasanenvelopetotheflower，orastamenproduceefficientpollen;yetthisoccurswithmanypeloricflowers。Thatpelorismisnotduetomerechancevariability，buteithertoanarrestofdevelopmentortoreversion，wemayinferfromanobservationmadebyCh。Morren（13/70。InhisdiscussiononsomecuriouspeloricCalceolariasquotedin’JournalofHorticulture’February24，1863page152。）namely，thatfamilieswhichhaveirregularflowersoften"returnbythesemonstrousgrowthstotheirregularform;whilstweneverseearegularflowerrealisethestructureofanirregularone。"
Someflowershavealmostcertainlybecomemoreorlesscompletelypeloricthroughreversion，asthefollowinginterestingcaseshows。Corydalistuberosaproperlyhasoneofitstwonectariescolourless，destituteofnectar，onlyhalfthesizeoftheother，andtherefore，toacertainextent，inarudimentarystate;thepistiliscurvedtowardstheperfectnectary，andthehood，formedof...完整阅读请扫描二维码下载丁香书院APP免费看：