respiratory　organs。　　Even　when　these　and　other　emotions　or　sensations　are　aroused　in　a　very　feeble　manner；　there　will　still　be　a　tendency　to　similar　actions；　owing　to　the　force　of　long…associated　habit；　and　those　actions　which　are　least　under　voluntary　control　will　generally　be　longest　retained。　Our　second　principle　of　antithesis　has　likewise　occasionally　come　into　play。
  Finally；　so　many　expressive　movements　can　be　explained；　as　I　trust　will　be　seen　in　the　course　of　this　volume；　through　the　three　principles　which　have　now　been　discussed；　that　we　may　hope　hereafter　to　see　all　thus　explained；　or　by　closely　analogous　principles。　It　is；　however；　often　impossible　to　decide　how　much　weight　ought　to　be　attributed；　in　each　particular　case；　to　one　of　our　principles；　and　how　much　to　another；　and　very　many　points　in　the　theory　of　Expression　remain　inexplicable。　　CHAPTER　IV。
  MEANS　OF　EXPRESSION　IN　ANIMALS。
  The　emission　of　SoundsVocal　soundsSounds　otherwise　produced　Erection　of　the　dermal　appendages；　hairs；　feathers；　&c。；　under　the　emotions　of　anger　and　terrorThe　drawing　back　of　the　ears　as　a　preparation　for　fighting；　and　as　an　expression　of　anger　Erection　of　the　ears　and　raising　the　head；　a　sign　of　attention。
  IN　this　and　the　following　chapter　I　will　describe；　but　only　in　sufficient　detail　to　illustrate　my　subject；　the　expressive　movements；　under　different　states　of　the　mind；　of　some　few　well…known　animals。　But　before　considering　them　in　due　succession；　it　will　save　much　useless　repetition　to　discuss　certain　means　of　expression　common　to　most　of　them。
  _The　emission　of　Sounds_。With　many　kinds　of　animals；　man　included；　the　vocal　organs　are　efficient　in　the　highest　degree　as　a　means　of　expression。　We　have　seen；　in　the　last　chapter；　that　when　the　sensorium　is　strongly　excited；　the　muscles　of　the　body　are　generally　thrown　into　violent　action；　and　as　a　consequence；　loud　sounds　are　uttered；　however　silent　the　animal　may　generally　be；　and　although　the　sounds　may　be　of　no　use。　Hares　and　rabbits　for　instance；　never；　I　believe；　use　their　vocal　organs　except　in　the　extremity　of　suffering；　as；　when　a　wounded　hare　is　killed　by　the　sportsman；　or　when　a　young　rabbit　is　caught　by　a　stoat。　Cattle　and　horses　suffer　great　pain　in　silence；　but　when　this　is　excessive；　and　especially　when　associated　with　terror；　they　utter　fearful　sounds。　I　have　often　recognized；　from　a　distance　on　the　Pampas；　the　agonized　death…bellow　of　the　cattle；　when　caught　by　the　lasso　and　hamstrung。　It　is　said　that　horses；　when　attacked　by　wolves；　utter　loud　and　peculiar　screams　of　distress。
  Involuntary　and　purposeless　contractions　of　the　muscles　of　the　chest　and　glottis；　excited　in　the　above　manner；　may　have　first　given　rise　to　the　emission　of　vocal　sounds。　　But　the　voice　is　now　largely　used　by　many　animals　for　various　purposes；　and　habit　seems　to　have　played　an　important　part　in　its　employment　under　other　circumstances。　Naturalists　have　remarked；　I　believe　with　truth；　that　social　animals；　from　habitually　using　their　vocal　organs　as　a　means　of　intercommunication；　use　them　on　other　occasions　much　more　freely　than　other　animals。　But　there　are　marked　exceptions　to　this　rule；　for　instance；　with　the　rabbit。　The　principle；　also；　of　association；　which　is　so　widely　extended　in　its　power；　has　likewise　played　its　part。　　Hence　it　follows　that　the　voice；　from　having　been　habitually　employed　as　a　serviceable　aid　under　certain　conditions；　inducing　pleasure；　pain；　rage；　&c；；　is　commonly　used　whenever　the　same　sensations　or　emotions　are　excited；　under　quite　different　conditions；　or　in　a　lesser　degree。
  The　sexes　of　many　animals　incessantly　call　for　each　other　during　the　breeding…season；　and　in　not　a　few　cases；　the　male　endeavours　thus　to　charm　or　excite　the　female。　　This；　indeed；　seems　to　have　been　the　primeval　use　and　means　of　development　of　the　voice；　as　I　have　attempted　to　show　in　my　‘Descent　of　Man。'　　Thus　the　use　of　the　vocal　organs　will　have　become　associated　with　the　anticipation　of　the　strongest　pleasure　which　animals　are　capable　of　feeling。　Animals　which　live　in　society　often　call　to　each　other　when　separated；　and　evidently　feel　much　joy　at　meeting；　as　we　see　with　a　horse；　on　the　return　of　his　companion；　for　whom　he　has　been　neighing。　The　mother　calls　incessantly　for　her　lost　young　ones；　for　instance；　a　cow　for　her　calf；　and　the　young　of　many　animals　call　for　their　mothers。　When　a　flock　of　sheep　is　scattered；　the　ewes　bleat　incessantly　for　their　lambs；　and　their　mutual　pleasure　at　coming　together　is　manifest。　Woe　betide　the　man　who　meddles　with　the　young　of　the　larger　and　fiercer　quadrupeds；　if　they　hear　the　cry　of　distress　from　their　young。　Rage　leads　to　the　violent　exertion　of　all　the　muscles；　including　those　of　the　voice；　and　some　animals；　when　enraged；　endeavour　to　strike　terror　into　their　enemies　by　its　power　and　harshness；　as　the　lion　does　by　roaring；　and　the　dog　by　growling。　　I　infer　that　their　object　is　to　strike　terror；　because　the　lion　at　the　same　time　erects　the　hair　of　its　mane；　and　the　dog　the　hair　along　its　back；　and　thus　they　make　themselves　appear　as　large　and　terrible　as　possible。　Rival　males　try　to　excel　and　challenge　each　other　by　their　voices；　and　this　leads　to　deadly　contests。　　Thus　the　use　of　the　voice　will　have　become　associated　with　the　emotion　of　anger；　however　it　may　be　aroused。　We　have　also　seen　that　intense　pain；　like　rage；　leads　to　violent　outcries；　and　the　exertion　of　screaming　by　itself　gives　some　relief；　and　thus　the　use　of　the　voice　will　have　become　associated　with　suffering　of　any　kind。
  The　cause　of　widely　different　sounds　being　uttered　under　different　emotions　and　sensations　is　a　very　obscure　subject。　　Nor　does　the　rule　always　hold　good　that　there　is　any　marked　difference。　For　instance　with　the　dog；　the　bark　of　anger　and　that　of　joy　do　not　differ　much；　though　they　can　be　distinguished。　It　is　not　probable　that　any　precise　explanation　of　the　cause　or　source　of　each　particular　sound；　under　different　states　of　the　mind；　will　ever　be　given。　　We　now　that　some　animals；　after　being　domesticated；　have　acquired　the　habit　of　uttering　sounds　which　were　not　natural　to　them。＇1＇　Thus　domestic　dogs；　and　even　tamed　jackals；　have　learnt　to　bark；　which　is　a　noise　not　proper　to　any　species　of　the　genus；　with　the　exception　of　the　_Canis　latrans_　of　North　America；　which　is　said　to　bark。　Some　breeds；　also；　of　the　domestic　pigeon　have　learnt　to　coo　in　a　new　and　quite　peculiar　manner。
  The　character　of　the　human　voice；　under　the　influence　of　various　emotions；　has　been　discussed　by　Mr。　Herbert　Spencer＇2＇　in　his　interesting　essay　on　Music。　　He　clearly　shows　that　the　voice　alters　much　under　different　conditions；　in　loudness　and　in　quality；　that　is；　in　resonance　and　_timbre_；　in　pitch　and　intervals。　No　one　can　listen　to　an　eloquent　orator　or　preacher；　or　to　a　man　calling　angrily　to　another；　or　to　one　expressing　astonishment；　without　being　struck　with　the　truth　of　Mr。　Spencer's　remarks。　It　is　curious　how　early　in　life　the　modulation　of　the　voice　becomes　expressive。　　With　one　of　my　children；　under　the　age　of　two　years；　I　clearly　perceived　that　his　humph　of　assent　was　rendered　by　a　slight　modulation　strongly　emphatic；　and　that　by　a　peculiar　whine　his　negative　expressed　obstinate　determination。　Mr。　Spencer　further　shows　that　emotional　speech；　in　all　the　above　respects　is　intimately　related　to　vocal　music；　and　consequently　to　instrumental　music；　and　he　attempts　to　explain　the　characteristic　qualities　of　both　on　physiological　groundsnamely；　on　〃the　general　law　that　a　feeling　is　a　stimulus　to　muscular　action。〃　It　may　be　admitted　that　the　voice　is　affected　through　this　law；　but　the　explanation　appears　to　me　too　general　and　vague　to　throw　much　light　on　the　various　differences；　with　the　exception　of　that　of　loudness；　between　ordinary　speech　and　emotional　speech；　or　singing。
  ＇1＇　See　the　evidence　on　this　head　in　my　‘Variation　of　Animals　and　Plants　under　Domestication；'　vol。　　i。　　p。　　27。　　On　the　cooing　of　pigeons；　vol。　　i。　　pp。　　154；　155。
  ＇2＇　‘Essays；　Scientific；　Political；　and　Speculative；'　1858。　‘The　Origin　and　Function　of　Music；'　p。　　359。
  This　remark　holds　good；　whether　we　believe　that　the　various　qualities　of　the　voice　originated　in　speaking　under　the　excitement　of　strong　feelings；　and　that　these　qualities　have　subsequently　been　transferred　to　vocal　music；　or　whether　we　believe；　as　I　maintain；　that　the　habit　of　uttering　musical　sounds　was　first　developed；　as　a　means　of　courtship；　in　the　early　progenitors　of　man；　and　thus　became　associated　with　the　strongest　emotions　of　which　they　were　capable；namely；　ardent　love；　rivalry　and　triumph。　That　animals　utter　musical　notes　is　familiar　to　every　one；　as　we　may　daily　hear　in　the　singing　of　birds。　　It　is　a　more　remarkable　fact　that　an　ape；　one　of　the　Gibbons；　produces　an　exact　octave　of　musical　sounds；　ascending　and　descending　the　scale　by　halftones；　so　that　this　monkey　〃alone　of　brute　mammals　may　be　said　to　sing。〃＇3＇　From　this　fact；　and　from　the　analogy　of　other　animals；　I　have　been　led　to　infer　that　the　progenitors　of　man　probably　uttered　musical　tones；　before　they　had　acquired　the　power　of　articulate　speech；　and　that　consequently；　when　the　voice　is　used　under　any　strong　emotion；　it　tends　to　assume；　through　the　principle　of　asso