the expression of emotion in man and animals-第23章

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　body　against　each　other；〃　whilst　the　head　remains　in　almost　the　same　position。　The　scales　on　the　sides；　and　not　on　other　parts　of　the　body；　are　strongly　keeled；　with　the　keels　toothed　like　a　saw；　and　as　the　coiled…up　animal　rubs　its　sides　together；　these　grate　against　each　other。＇26＇　Lastly；　we　have　the　well…known　case　of　the　Rattle…snake。　He　who　has　merely　shaken　the　rattle　of　a　dead　snake；　can　form　no　just　idea　of　the　sound　produced　by　the　living　animal。　Professor　Shaler　states　that　it　is　indistinguishable　from　that　made　by　the　male　of　a　large　Cicada　（an　Homopterous　insect）；　which　inhabits　the　same　district。＇27＇　In　the　Zoological　Gardens；　when　the　rattle…snakes　and　puff…adders　were　greatly　excited　at　the　same　time；　I　was　much　struck　at　the　similarity　of　the　sound　produced　by　them；　and　although　that　made　by　the　rattle…snake　is　louder　and　shriller　than　the　hissing　of　the　puff…adder；　yet　when　standing　at　some　yards　distance　I　could　scarcely　distinguish　the　two。　For　whatever　purpose　the　sound　is　produced　by　the　one　species；　I　can　hardly　doubt　that　it　serves　for　the　same　purpose　in　the　other　species；　and　I　conclude　from　the　threatening　gestures　made　at　the　same　time　by　many　snakes；　that　their　hissing；the　rattling　of　the　rattle…snake　and　of　the　tail　of　the　Trigonocephalus；the　grating　of　the　scales　of　the　Echis；and　the　dilatation　of　the　hood　of　the　Cobra；　all　subserve　the　same　end；　namely；　to　make　them　appear　terrible　to　their　enemies。＇28＇


＇24＇　Mr。　J。　Mansel　Weale；　‘Nature；'　April　27；　1871；　p。　　508。

＇25＇　‘Journal　of　Researches　during　the　Voyage　of　the　〃Beagle；〃　'　1845；　p。　　96。　　I　have　compared　the　rattling　thus　produced　with　that　of　the　Rattle…snake。

＇26＇　See　the　account　by　Dr。　Anderson；　Proc。　　Zool。　　Soc。　　1871；　p。　　196。

＇27＇　The　‘American　Naturalist；'　Jan。　1872；　p。　　32。　　I　regret　that　I　cannot　follow　Prof。　Shaler　in　believing　that　the　rattle　has　been　developed；　by　the　aid　of　natural　selection；　for　the　sake　of　producing　sounds　which　deceive　and　attract　birds；　so　that　they　may　serve　as　prey　to　the　snake。

It　seems　at　first　a　probable　conclusion　that　venomous　snakes；　such　as　the　foregoing；　from　being　already　so　well　defended　by　their　poison…fangs；　would　never　be　attacked　by　any　enemy；　and　consequently　would　have


｛note　＇27＇　continued｝　I　do　not；　however；　wish　to　doubt　that　the　sounds　may　occasionally　subserve　this　end。　But　the　conclusion　at　which　I　have　arrived；　viz。　　that　the　rattling　serves　as　a　warning　to　would…be　devourers；　appears　to　me　much　more　probable；　as　it　connects　together　various　classes　of　facts。　If　this　snake　had　acquired　its　rattle　and　the　habit　of　rattling；　for　the　sake　of　attracting　prey；　it　does　not　seem　probable　that　it　would　have　invariably　used　its　instrument　when　angered　or　disturbed。　Prof。　Shaler　takes　nearly　the　same　view　as　I　do　of　the　manner　of　development　of　the　rattle；　and　I　have　always　held　this　opinion　since　observing　the　Trigonocephalus　in　South　America。

＇28＇　From　the　accounts　lately　collected；　and　given　in　the　‘Journal　of　the　Linnean　Society；'　by　Airs。　　Barber；　on　the　habits　of　the　snakes　of　South　Africa；　and　from　the　accounts　published　by　several　writers；　for　instance　by　Lawson；　of　the　rattle…snake　in　North　America；it　does　not　seem　improbable　that　the　terrific　appearance　of　snakes　and　the　sounds　produced　by　them；　may　likewise　serve　in　procuring　prey；　by　paralysing；　or　as　it　is　sometimes　called　fascinating；　the　smaller　animals。　no　need　to　excite　additional　terror。　　But　this　is　far　from　being　the　case；　for　they　are　largely　preyed　on　in　all　quarters　of　the　world　by　many　animals。　It　is　well　known　that　pigs　are　employed　in　the　United　States　to　clear　districts　infested　with　rattle…snakes；　which　they　do　most　effectually。＇29＇　In　England　the　hedgehog　attacks　and　devours　the　viper。　In　India；　as　I　hear　from　Dr。　Jerdon；　several　kinds　of　hawks；　and　at　least　one　mammal；　the　Herpestes；　kill　cobras　and　other　venomous　species；＇30＇　and　so　it　is　in　South　Africa。　　Therefore　it　is　by　no　means　improbable　that　any　sounds　or　signs　by　which　the　venomous　species　could　instantly　make　themselves　recognized　as　dangerous；　would　be　of　more　service　to　them　than　to　the　innocuous　species　which　would　not　be　able；　if　attacked；　to　inflict　any　real　injury。

Having　said　thus　much　about　snakes；　I　am　tempted　to　add　a　few　remarks　on　the　means　by　which　the　rattle　of　the　rattle…snake　was　probably　developed。　Various　animals；　including　some　lizards；　either　curl　or　vibrate　their　tails　when　excited。　　This　is　the　case　with　many　kinds　of　snakes。＇31＇　In　the　Zoological　Gardens；　an　innocuous　species；　the　_Coronella　Sayi_；　vibrates　its　tail　so　rapidly　that　it　becomes　almost　invisible。　The　Trigonocephalus；　before　alluded　to；　has　the　same　habit；　and　the　extremity　of　its　tail　is　a　little　enlarged；　or　ends　in　a　bead。　In　the　Lachesis；　which　is　so　closely　allied　to　the　rattle…snake　that　it　was　placed　by　Linnaeus　in　the　same　genus；　the　tail　ends　in　a　single；　large；　lancet…shaped　point　or　scale。　　With　some　snakes　the　skin；　as　Professor　Shaler　remarks；　〃is　more　imperfectly　detached　from　the　region　about　the　tail　than　at　other　parts　of　the　body。〃　Now　if　we　suppose　that　the　end　of　the　tail　of　some　ancient　American　species　was　enlarged；　and　was　covered　by　a　single　large　scale；　this　could　hardly　have　been　cast　off　at　the　successive　moults。　In　this　case　it　would　have　been　permanently　retained；　and　at　each　period　of　growth；　as　the　snake　grew　larger；　a　new　scale；　larger　than　the　last；　would　have　been　formed　above　it；　and　would　likewise　have　been　retained。　The　foundation　for　the　development　of　a　rattle　would　thus　have　been　laid；　and　it　would　have　been　habitually　used；　if　the　species；　like　so　many　others；　vibrated　its　tail　whenever　it　was　irritated。　That　the　rattle　has　since　been　specially　developed　to　serve　as　an　efficient　sound…producing　instrument；　there　can　hardly　be　a　doubt；　for　even　the　vertebrae　included　within　the　extremity　of　the　tail　have　been　altered　in　shape　and　cohere。　　But　there　is　no　greater　improbability　in　various　structures；　such　as　the　rattle　of　the　rattle…snake；　the　lateral　scales　of　the　Echis；the　neck　with　the　included　ribs　of　the　Cobra；and　the　whole　body　of　the　puff…adder；having　been　modified　for　the　sake　of　warning　and　frightening　away　their　enemies；　than　in　a　bird；　namely；　the　wonderful　Secretary…hawk　（_Gypogeranus_）　having　had　its　whole　frame　modified　for　the　sake　of　killing　snakes　with　impunity。　It　is　highly　probable；　judging　from　what　we　have　before　seen；　that　this　bird　would　ruffle　its　feathers　whenever　it　attacked　a　snake；　and　it　is　certain　that　the　Herpestes；　when　it　eagerly　rushes　to　attack　a　snake；　erects　the　hair　all　over　its　body；　and　especially　that　on　its　tail。＇32＇　We　have　also　seen　that　some　porcupines；　when　angered　or　alarmed　at　the　sight　of　a　snake；　rapidly　vibrate　their　tails；　thus　producing　a　peculiar　sound　by　the　striking　together　of　the　hollow　quills。　So　that　here　both　the　attackers　and　the　attacked　endeavour　to　make　themselves　as　dreadful　as　possible　to　each　other；　and　both　possess　for　this　purpose　specialised　means；　which；　oddly　enough；　are　nearly　the　same　in　some　of　these　cases。　　Finally　we　can　see　that　if；　on　the　one　hand；　those　individual　snakes；　which　were　best　able　to　frighten　away　their　enemies；　escaped　best　from　being　devoured；　and　if；　on　the　other　hand；　those　individuals　of　the　attacking　enemy　survived　in　larger　numbers　which　were　the　best　fitted　for　the　dangerous　task　of　killing　and　devouring　venomous　snakes；　then　in　the　one　case　as　in　the　other；　beneficial　variations；　supposing　the　characters　in　question　to　vary；　would　commonly　have　been　preserved　through　the　survival　of　the　fittest。


＇29＇　See　the　account　by　Dr。　R。　Brown；　in　Proc。　　Zool。　　Soc。　　1871；　p。　　39。　He　says　that　as　soon　as　a　pig　sees　a　snake　it　rushes　upon　it；　and　a　snake　makes　off　immediately　on　the　appearance　of　a　pig。

＇30＇　Dr。　Gunther　remarks　（‘Reptiles　of　British　India；'　p。　　340）　on　the　destruction　of　cobras　by　the　ichneumon　or　herpestes；　and　whilst　the　cobras　are　young　by　the　jungle…fowl。　It　is　well　known　that　the　peacock　also　eagerly　kills　snakes。

＇31＇　Prof。　Cope　enumerates　a　number　of　kinds　in　his　‘Method　of　Creation　of　Organic　Types；'　read　before　the　American　Phil。　　Soc。；　December　15th；　1871；　p。　　20。　　Prof。　Cope　takes　the