cognized　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　same　view　as　I　do　of　the　use　of　the　gestures　and　sounds　made　by　snakes。　　I　briefly　alluded　to　this　subject　in　the　last　edition　of　my　‘Origin　of　Species。'　　Since　the　passages　in　the　text　above　have　been　printed；　I　have　been　pleased　to　find　that　Mr。　Henderson　（‘The　American　Naturalist；'　May；　1872；　p。　　260）　also　takes　a　similar　view　of　the　use　of　the　rattle；　namely　〃in　preventing　an　attack　from　being　made。〃
  _The　Drawing　back　and　pressure　of　the　Ears　to　the　Head_。The　ears　through　their　movements　are　highly　expressive　in　many　animals；　but　in　some；　such　as　man；　the　higher　apes；　and　many　ruminants；　they　fail　in　this　respect。　　A　slight　difference　in　position　serves　to　express　in　the　plainest　manner　a　different　state　of　mind；　as　we　may　daily　see　in　the　dog；　but　we　are　here　concerned　only　with　the　ears　being　drawn　closely　backwards　and　pressed　to　the　head。　A　savage　frame　of　mind　is　thus　shown；　but　only　in　the　case　of　those　animals　which　fight　with　their　teeth；　and　the　care　which　they　take　to　prevent　their　ears　being　seized　by　their　antagonists；　accounts　for　this　position。　　Consequently；　through　habit　and　association；　whenever　they　feel　slightly　savage；　or　pretend　in　their　play　to　be　savage；　their　ears　are　drawn　back。　That　this　is　the　true　explanation　may　be　inferred　from　the　relation　which　exists　in　very　many　animals　between　their　manner　of　fighting　and　the　retraction　of　their　ears。
  ＇32＇　Mr。　des　Voeux；　in　Proc。　　Zool。　　Soc。　　1871；　p。　　3。
  All　the　Carnivora　fight　with　their　canine　teeth；　and　all；　as　far　as　I　have　observed；　draw　their　ears　back　when　feeling　savage。　This　may　be　continually　seen　with　dogs　when　fighting　in　earnest；　and　with　puppies　fighting　in　play。　　The　movement　is　different　from　the　falling　down　and　slight　drawing　back　of　the　ears；　when　a　dog　feels　pleased　and　is　caressed　by　his　master。　The　retraction　of　the　ears　may　likewise　be　seen　in　kittens　fighting　together　in　their　play；　and　in　full…grown　cats　when　really　savage；　as　before　illustrated　in　fig。　　9　（p。　58）。　Although　their　ears　are　thus　to　a　large　extent　protected；　yet　they　often　get　much　torn　in　old　male　cats　during　their　mutual　battles。　The　same　movement　is　very　striking　in　tigers；　leopards；　&c。；　whilst　growling　over　their　food　in　menageries。　The　lynx　has　remarkably　long　ears；　and　their　retraction；　when　one　of　these　animals　is　approached　in　its　cage；　is　very　conspicuous；　and　is　eminently　expressive　of　its　savage　disposition。　Even　one　of　the　Eared　Seals；　the　_Otariapusilla_；　which　has　very　small　ears；　draws　them　backwards；　when　it　makes　a　savage　rush　at　the　legs　of　its　keeper。
  When　horses　fight　together　they　use　their　incisors　for　biting；　and　their　fore…legs　for　striking；　much　more　than　they　do　their　hind…legs　for　kicking　backwards。　　This　has　been　observed　when　stallions　have　broken　loose　and　have　fought　together；　and　may　likewise　be　inferred　from　the　kind　of　wounds　which　they　inflict　on　each　other。　　Every　one　recognizes　the　vicious　appearance　which　the　drawing　back　of　the　ears　gives　to　a　horse。　This　movement　is　very　different　from　that　of　listening　to　a　sound　behind。　If　an　ill…tempered　horse　in　a　stall　is　inclined　to　kick　backwards；　his　ears　are　retracted　from　habit；　though　he　has　no　intention　or　power　to　bite。　But　when　a　horse　throws　up　both　hind…legs　in　play；　as　when　entering　an　open　field；　or　when　just　touched　by　the　whip；　he　does　not　generally　depress　his　ears；　for　he　does　not　then　feel　vicious。　　Guanacoes　fight　savagely　with　their　teeth；　and　they　must　do　so　frequently；　for　I　found　the　hides　of　several　which　I　shot　in　Patagonia　deeply　scored。　　So　do　camels；　and　both　these　animals；　when　savage；　draw　their　ears　closely　backwards。　Guanacoes；　as　I　have　noticed；　when　not　intending　to　bite；　but　merely　to　spit　their　offensive　saliva　from　a　distance　at　an　intruder；　retract　their　ears。　Even　the　hippopotamus；　when　threatening　with　its　widely…open　enormous　mouth　a　comrade；　draws　back　its　small　ears；　just　like　a　horse。
  Now　what　a　contrast　is　presented　between　the　foregoing　animals　and　cattle；　sheep；　or　goats；　which　never　use　their　teeth　in　fighting；　and　never　draw　back　their　ears　when　enraged！　　Although　sheep　and　goats　appear　such　placid　animals；　the　males　often　join　in　furious　contests。　As　deer　form　a　closely　related　family；　and　as　I　did　not　know　that　they　ever　fought　with　their　teeth；　I　was　much　surprised　at　the　account　given　by　Major　Ross　King　of　the　Moose…deer　in　Canada。　　He　says；　when　〃two　males　chance　to　meet；　laying　back　their　ears　and　gnashing　their　teeth　together；　they　rush　at　each　other　with　appalling　fury。〃＇33＇　But　Mr。　Bartlett　informs　me　that　some　species　of　deer　fight　savagely　with　their　teeth；　so　that　the　drawing　back　of　the　ears　by　the　moose　accords　with　our　rule。　Several　kinds　of　kangaroos；　kept　in　the　Zoological　Gardens；　fight　by　scratching　with　their　fore…feet　and　by　kicking　with　their　hind…legs；　but　they　never　bite　each　other；　and　the　keepers　have　never　seen　them　draw　back　their　ears　when　angered。　　Rabbits　fight　chiefly　by　kicking　and　scratching；　but　they　likewise　bite　each　other；　and　I　have　known　one　to　bite　off　half　the　tail　of　its　antago