Dogs　scratch　themselves　by　a　rapid　movement　of　one　of　their　hind…feet；　and　when　their　backs　are　rubbed　with　a　stick；　so　strong　is　the　habit；　that　they　cannot　help　rapidly　scratching　the　air　or　the　ground　in　a　useless　and　ludicrous　manner。　　The　terrier　just　alluded　to；　when　thus　scratched　with　a　stick；　will　sometimes　show　her　delight　by　another　habitual　movement；　namely；　by　licking　the　air　as　if　it　were　my　hand。
  Horses　scratch　themselves　by　nibbling　those　parts　of　their　bodies　which　they　can　reach　with　their　teeth；　but　more　commonly　one　horse　shows　another　where　he　wants　to　be　scratched；　and　they　then　nibble　each　other。　A　friend　whose　attention　I　had　called　to　the　subject；　observed　that　when　he　rubbed　his　horse's　neck；　the　animal　protruded　his　head；　uncovered　his　teeth；　and　moved　his　jaws；　exactly　as　if　nibbling　another　horse's　neck；　for　he　could　never　have　nibbled　his　own　neck。　If　a　horse　is　much　tickled；　as　when　curry…combed；　his　wish　to　bite　something　becomes　so　intolerably　strong；　that　he　will　clatter　his　teeth　together；　and　though　not　vicious；　bite　his　groom。　At　the　same　time　from　habit　he　closely　depresses　his　ears；　so　as　to　protect　them　from　being　bitten；　as　if　he　were　fighting　with　another　horse。
  A　horse　when　eager　to　start　on　a　journey　makes　the　nearest　approach　which　he　can　to　the　habitual　movement　of　progression　by　pawing　the　ground。　Now　when　horses　in　their　stalls　are　about　to　be　fed　and　are　eager　for　their　corn；　they　paw　the　pavement　or　the　straw。　　Two　of　my　horses　thus　behave　when　they　see　or　hear　the　corn　given　to　their　neighbours。　But　here　we　have　what　may　almost　be　called　a　true　expression；　as　pawing　the　ground　is　universally　recognized　as　a　sign　of　eagerness。
  Cats　cover　up　their　excrements　of　both　kinds　with　earth；　and　my　grandfather＇17＇｛sic｝　saw　a　kitten　scraping　ashes　over　a　spoonful　of　pure　water　spilt　on　the　hearth；　so　that　here　an　habitual　or　instinctive　action　was　falsely　excited；　not　by　a　previous　act　or　by　odour；　but　by　eyesight。　　It　is　well　known　that　cats　dislike　wetting　their　feet；　owing；　it　is　probable；　to　their　having　aboriginally　inhabited　the　dry　country　of　Egypt；　and　when　they　wet　their　feet　they　shake　them　violently。　My　daughter　poured　some　water　into　a　glass　close　to　the　head　of　a　kitten；　and　it　immediately　shook　its　feet　in　the　usual　manner；　so　that　here　we　have　an　habitual　movement　falsely　excited　by　an　associated　sound　instead　of　by　the　sense　of　touch。
  Kittens；　puppies；　young　pigs　and　probably　many　other　young　animals；　alternately　push　with　their　forefeet　against　the　mammary　glands　of　their　mothers；　to　excite　a　freer　secretion　of　milk；　or　to　make　it　flow。　　Now　it　is　very　common　with　young　cats；　and　not　at　all　rare　with　old　cats　of　the　common　and　Persian　breeds　（believed　by　some　naturalists　to　be　specifically　extinct）；　when　comfortably　lying　on　a　warm　shawl　or　other　soft　substance；　to　pound　it　quietly　and　alternately　with　their　fore…feet；　their　toes　being　spread　out　and　claws　slightly　protruded；　precisely　as　when　sucking　their　mother。　　That　it　is　the　same　movement　is　clearly　shown　by　their　often　at　the　same　time　taking　a　bit　of　the　shawl　into　their　mouths　and　sucking　it；　generally　closing　their　eyes　and　purring　from　delight。　This　curious　movement　is　commonly　excited　only　in　association　with　the　sensation　of　a　warm　soft　surface；　but　I　have　seen　an　old　cat；　when　pleased　by　having　its　back　scratched；　pounding　the　air　with　its　feet　in　the　same　manner；　so　that　this　action　has　almost　become　the　expression　of　a　pleasurable　sensation。
  ＇16＇〃Dr。　Darwin；　‘Zoonomia；'　1794；　vol。　　i。　　p。　　160。　　I　find　that　the　fact　of　cats　protruding　their　feet　when　pleased　is　also　noticed　（p。　151）　in　this　work。
  Having　referred　to　the　act　of　sucking；　I　may　add　that　this　complex　movement；　as　well　as　the　alternate　protrusion　of　the　fore…feet；　are　reflex　actions；　for　they　are　performed　if　a　finger　moistened　with　milk　is　placed　in　the　mouth　of　a　puppy；　the　front　part　of　whose　brain　has　been　removed。＇17＇　It　has　recently　been　stated　in　France；　that　the　action　of　sucking　is　excited　solely　through　the　sense　of　smell；　so　that　if　the　olfactory　nerves　of　a　puppy　are　destroyed；　it　never　sucks。　In　like　manner　the　wonderful　power　which　a　chicken　possesses　only　a　few　hours　after　being　hatched；　of　picking　up　small　particles　of　food；　seems　to　be　started　into　action　through　the　sense　of　hearing；　for　with　chickens　hatched　by　artificial　heat；　a　good　observer　found　that　〃making　a　noise　with　the　finger…nail　against　a　board；　in　imitation　of　the　hen…mother；　first　taught　them　to　peck　at　their　meat。〃＇18＇
  ＇17＇　Carpenter；　‘Principles　of　Comparative　Physiology；'　1854；　p。　　690；　and　Muller's　‘Elements　of　Physiology；'　Eng。　　translat。　　vol。　　ii。　　p。　　936。
  ＇18＇　Mowbray　on　‘Poultry；'　6th　edit。　　1830；　p。　　54。
  I　will　give　only　one　other　instance　of　an　habitual　and　purposeless　movement。　　The　Sheldrake　（_Tadorna_）　feeds　on　the　sands　left　uncovered　by　the　tide；　and　when　a　worm…cast　is　discovered；　〃it　begins　patting　the　ground　with　its　feet；　dancing　as　it　were；　over　the　hole；〃　and　this　makes　the　worm　come　to　the　surface。　Now　Mr。　St。　John　says；　that　when　his　tame　Sheldrakes　〃came　to　ask　for　food；　they　patted　the　ground　in　an　impatient　and　rapid　manner。〃＇19＇　This　therefore　may　almost　be　considered　as　their　expression　of　hunger。　　Mr。　Bartlett　informs　me　that　the　Flamingo　and　the　Kagu　（_Rhinochetus　jubatus_）　when　anxious　to　be　fed；　beat　the　ground　with　their　feet　in　the　same　odd　manner。　So　again　Kingfishers；　when　they　catch　a　fish；　always　beat　it　until　it　is　killed；　and　in　the　Zoological　Gardens　they　always　beat　the　raw　meat；　with　which　they　are　sometimes　fed；　before　devouring　it。
  We　have　now；　I　think；　sufficiently　shown　the　truth　of　our　first　Principle；　namely；　that　when　any　sensation；　desire；　dislike；　&c。；　has　led　during　a　long　series　of　generations　to　some　voluntary　movement；　then　a　tendency　to　the　performance　of　a　similar　movement　will　almost　certainly　be　excited；　whenever　the　same；　or　any　analogous　or　associated　sensation　&c。；　although　very　weak；　is　experienced；　notwithstanding　that　the　movement　in　this　case　may　not　be　of　the　least　use。　　Such　habitual　movements　are　often；　or　generally　inherited；　and　they　then　differ　but　little　from　reflex　actions。　When　we　treat　of　the　special　expressions　of　man；　the　latter　part　of　our　first　Principle；　as　given　at　the　commencement　of　this　chapter；　will　be　seen　to　hold　good；　namely；　that　when　movements；　associated　through　habit　with　certain　states　of　the　mind；　are　partially　repressed　by　the　will；　the　strictly　involuntary　muscles；　as　well　as　those　which　are　least　under　the　separate　control　of　the　will；　are　liable　still　to　act；　and　their　action　is　often　highly　expressive。　　Conversely；　when　the　will　is　temporarily　or　permanently　weakened；　the　voluntary　muscles　fail　before　the　involuntary。　　It　is　a　fact　familiar　to　pathologists；　as　Sir　C。　Bell　remarks；＇20＇　〃that　when　debility　arises　from　affection　of　the　brain；　the　influence　is　greatest　on　those　muscles　which　are；　in　their　natural　condition；　most　under　the　command　of　the　will。〃　We　shall；　also；　in　our　future　chapters；　consider　another　proposition　included　in　our　first　Principle；　namely；　that　the　checking　of　one　habitual　movement　sometimes　requires　other　slight　movements；　these　latter　serving　as　a　means　of　expression。
  ＇19＇　See　the　account　given　by　this　excellent　observer　in　‘Wild　Sports　of　the　Highlands；'　1846；　p。　　142。
  ＇20＇　‘Philosophical　Translations；'　1823；　p。　　182。
  CHAPTER　II。
  GENERAL　PRINCIPLES　OF　EXPRESSION_continued_。
  The　Principle　of　AntithesisInstances　in　the　dog　and　cat　Origin　of　the　principleConventional　signsThe　principle　of　antithesis　has　not　arisen　from　opposite　actions　being　consciously　performed　under　opposite　impulses。
  WE　will　now　consider　our　second　Principle；　that　of　Antithesis。　　Certain　states　of　the　mind　lead；　as　we　have　seen　in　the　last　chapter；　to　certain　habitual　movements　which　were　primarily；　or　may　still　be；　of　service；　and　we　shall　find　that　when　a　directly　opposite　state　of　mind　is　induced；　there　is　a　strong　and　involuntary　tendency　to　the　performance　of　movements　of　a　directly　opposite　nature；　though　these　have　never　been　of　any　service。　A　few　striking　instances　of　antithesis　will　be　given；　when　we　treat　of　the　special　expressions　of　man；　but　as；　in　these　cases；　we　are　particularly　liable　to　confound　conventional　or　artificial　gestures　and　expressions　with　those　which　are　innate　or　universal；　and　which　alone　deserve　to　rank　as　true　expressions；　I　will　in　the　present　chapter　almost　confine　myself　to　the　lower　animals。
  When　a　dog　approaches　a　strange　dog　or　man　in　a　savage　or　hostile　frame　of　mind　be　walks　upright　and　very　stiffly；　his　head　is　slightly　raised；　or　not　much　lowered；　the　tail　is　held　erect；　and　quite　rigid；　the　hairs　bristle；　especially　along　the　neck　and　back；　the　pricked　ears　are　directed　forwards；　and　the　eyes　have　a　fixed　stare：　　（see　figs。　5　and　7）。　These　actions；　as　will　hereafter　be　explained；　follow　from　the　dog's　intention　to　attack　his　enemy；　and　are　thus　to　a　large　extent　intelligible。　As　he　prepares　to　spring　with　a　savage　growl　on　his　enemy；　the　canine　teeth　are　uncovered；　and　the　ears　are　pressed　close　backwards　on　the　head；　but　with　these　latter　actions；　we　are　not　here　co