quite　competent　to　account　for　all　that　we　may　call　purely　structural
  phenomena　which　are　exhibited　by　SPECIES　in　nature。　　On　that　point　also
  I　have　already　enlarged　somewhat。　　Again；　I　think　that　the　causes
  assumed　are　competent　to　account　for　most　of　the　physiological
  characteristics　of　species；　and　I　not　only　think　that　they　are
  competent　to　account　for　them；　but　I　think　that　they　account　for　many
  things　which　otherwise　remain　wholly　unaccountable　and　inexplicable；
  and　I　may　say　incomprehensible。　　For　a　full　exposition　of　the　grounds
  on　which　this　conviction　is　based；　I　must　refer　you　to　Mr。　　Darwin's
  work；　all　that　I　can　do　now　is　to　illustrate　what　I　have　said　by　two　or
  three　cases　taken　almost　at　random。
  I　drew　your　attention；　on　a　previous　evening；　to　the　facts　which　are
  embodied　in　our　systems　of　Classification；　which　are　the　results　of　the
  examination　and　comparison　of　the　different　members　of　the　animal
  kingdom　one　with　another。　　I　mentioned　that　the　whole　of　the　animal
  kingdom　is　divisible　into　five　sub…kingdoms；　that　each　of　these
  sub…kingdoms　is　again　divisible　into　provinces；　that　each　province　may
  be　divided　into　classes；　and　the　classes　into　the　successively　smaller
  groups；　orders；　families；　genera；　and　species。
  Now；　in　each　of　these　groups；　the　resemblance　in　structure　among　the
  members　of　the　group　is　closer　in　proportion　as　the　group　is　smaller。
  Thus；　a　man　and　a　worm　are　members　of　the　animal　kingdom　in　virtue　of
  certain　apparently　slight　though　really　fundamental　resemblances　which
  they　present。　　But　a　man　and　a　fish　are　members　of　the　same　sub…kingdom
  'Vertebrata'；　because　they　are　much　more　like　one　another　than　either
  of　them　is　to　a　worm；　or　a　snail；　or　any　member　of　the　other
  sub…kingdoms。　　For　similar　reasons　men　and　horses　are　arranged　as
  members　of　the　same　Class；　'Mammalia'；　men　and　apes　as　members　of　the
  same　Order；　'Primates'；　and　if　there　were　any　animals　more　like　men
  than　they　were　like　any　of　the　apes；　and　yet　different　from　men　in
  important　and　constant　particulars　of　their　organization；　we　should
  rank　them　as　members　of　the　same　Family；　or　of　the　same　Genus；　but　as　of
  distinct　Species。
  That　it　is　possible　to　arrange　all　the　varied　forms　of　animals　into
  groups；　having　this　sort　of　singular　subordination　one　to　the　other；　is
  a　very　remarkable　circumstance；　but；　as　Mr。　Darwin　remarks；　this　is　a
  result　which　is　quite　to　be　expected；　if　the　principles　which　he　lays
  down　be　correct。　　Take　the　case　of　the　races　which　are　known　to　be
  produced　by　the　operation　of　atavism　and　variability；　and　the
  conditions　of　existence　which　check　and　modify　these　tendencies。　　Take
  the　case　of　the　pigeons　that　I　brought　before　you；　there　it　was　shown
  that　they　might　be　all　classed　as　belonging　to　some　one　of　five
  principal　divisions；　and　that　within　these　divisions　other　subordinate
  groups　might　be　formed。　　The　members　of　these　groups　are　related　to　one
  another　in　just　the　same　way　as　the　genera　of　a　family；　and　the　groups
  themselves　as　the　families　of　an　order；　or　the　orders　of　a　class；　while
  all　have　the　same　sort　of　structural　relations　with　the　wild
  rock…pigeon；　as　the　members　of　any　great　natural　group　have　with　a　real
  or　imaginary　typical　form。　　Now；　we　know　that　all　varieties　of　pigeons
  of　every　kind　have　arisen　by　a　process　of　selective　breeding　from　a
  common　stock；　the　rock…pigeon；　hence；　you　see；　that　if　all　species　of
  animals　have　proceeded　from　some　common　stock；　the　general　character　of
  their　structural　relations；　and　of　our　systems　of　classification；　which
  express　those　relations；　would　be　just　what　we　find　them　to　be。　　In
  other　words；　the　hypothetical　cause　is；　so　far；　competent　to　produce
  effects　similar　to　those　of　the　real　cause。
  Take；　again；　another　set　of　very　remarkable　facts；the　existence　of
  what　are　called　rudimentary　organs；　organs　for　which　we　can　find　no
  obvious　use；　in　the　particular　animal　economy　in　which　they　are　found；
  and　yet　which　are　there。
  Such　are　the　splint…like　bones　in　the　leg　of　the　horse；　which　I　here
  show　you；　and　which　correspond　with　bones　which　belong　to　certain　toes
  and　fingers　in　the　human　hand　and　foot。　In　the　horse　you　see　they　are
  quite　rudimentary；　and　bear　neither　toes　nor　fingers；　so　that　the　horse
  has　only　one　〃finger〃　in　his　fore…foot　and　one　〃toe〃　in　his　hind　foot。
  But　it　is　a　very　curious　thing　that　the　animals　closely　allied　to　the
  horse　show　more　toes　than　he；　as　the　rhinoceros；　for　instance：　he　has
  these　extra　toes　well　formed；　and　anatomical　facts　show　very　clearly
  that　he　is　very　closely　related　to　the　horse　indeed。　　So　we　may　say　that
  animals；　in　an　anatomical　sense　nearly　related　to　the　horse；　have　those
  parts　which　are　rudimentary　in　him；　fully　developed。
  Again；　the　sheep　and　the　cow　have　no　cutting…teeth；　but　only　a　hard　pad
  in　the　upper　jaw。　That　is　the　common　characteristic　of　ruminants　in
  general。　　But　the　calf　has　in　its　upper　jaw　some　rudiments　of　teeth
  which　never　are　developed；　and　never　play　the　part　of　teeth　at　all。
  Well；　if　you　go　back　in　time；　you　find　some　of　the　older；　now　extinct；
  allies　of　the　ruminants　have　well…developed　teeth　in　their　upper　jaws；
  and　at　the　present　day　the　pig　（which　is　in　structure　closely　connected
  with　ruminants）　has　well…developed　teeth　in　its　upper　jaw；　so　that　here
  is　another　instance　of　organs　well…developed　and　very　useful；　in　one
  animal；　represented　by　rudimentary　organs；　for　which　we　can　discover　no
  purpose　whatsoever；　in　another　closely　allied　animal。　　The　whalebone
  whale；　again；　has　horny　〃whalebone〃　plates　in　its　mouth；　and　no　teeth；
  but　the　young　foetal　whale；　before　it　is　born；　has　teeth　in　its　jaws；
  they；　however；　are　never　used；　and　they　never　come　to　anything。　　But
  other　members　of　the　group　to　which　the　whale　belongs　have
  well…developed　teeth　in　both　jaws。
  Upon　any　hypothesis　of　special　creation；　facts　of　this　kind　appear　to　me
  to　be　entirely　unaccountable　and　inexplicable；　but　they　cease　to　be　so
  if　you　accept　Mr。　Darwin's　hypothesis；　and　see　reason　for　believing
  that　the　whalebone　whale　and　the　whale　with　teeth　in　its　mouth　both
  sprang　from　a　whale　that　had　teeth；　and　that　the　teeth　of　the　foetal
  whale　are　merely　remnantsrecollections；　if　we　may　so　sayof　the
  extinct　whale。　　So　in　the　case　of　the　horse　and　the　rhinoceros：　suppose
  that　both　have　descended　by　modification　from　some　earlier　form　which
  had　the　normal　number　of　toes；　and　the　persistence　of　the　rudimentary
  bones　which　no　longer　support　toes　in　the　horse　becomes　comprehensible。
  In　the　language　that　we　speak　in　England；　and　in　the　language　of　the
  Greeks；　there　are　identical　verbal　roots；　or　elements　entering　into　the
  composition　of　words。　　That　fact　remains　unintelligible　so　long　as　we
  suppose　English　and　Greek　to　be　independently　created　tongues；　but　when
  it　is　shown　that　both　languages　are　descended　from　one　original；　the
  Sanscrit；　we　give　an　explanation　of　that　resemblance。　　In　the　same　way
  the　existence　of　identical　structural　roots；　if　I　may　so　term　them；
  entering　into　the　composition　of　widely　different　animals；　is　striking
  evidence　in　favour　of　the　descent　of　those　animals　from　a　common
  original。
  To　turn　to　another　kind　of　illustration：If　you　regard　the　whole　series
  of　stratified　rocksthat　enormous　thickness　of　sixty　or　seventy
  thousand　feet　that　I　have　mentioned　before；　constituting　the　only
  record　we　have　of　a　most　prodigious　lapse　of　time；　that　time　being；　in
  all　probability；　but　a　fraction　of　that　of　which　we　have　no　record；if
  you　observe　in　these　successive　strata　of　rocks　successive　groups　of
  animals　arising　and　dying　out；　a　constant　succession；　giving　you　the
  same　kind　of　impression；　as　you　travel　from　one　group　of　strata　to
  another；　as　you　would　have　in　travelling　from　one　country　to
  another；when　you　find　this　constant　succession　of　forms；　their　traces
  obliterated　except　to　the　man　of　science；when　you　look　at　this
  wonderful　history；　and　ask　what　it　means；　it　is　only　a　paltering　with
  words　if　you　are　offered　the　reply；'They　were　so　created。'
  But　if；　on　the　other　hand；　you　look　on　all　forms　of　organized　beings　as
  the　results　of　the　gradual　modification　of　a　primitive　type；　the　facts
  receive　a　meaning；　and　you　see　that　these　older　conditions　are　the
  necessary　predecessors　of　the　present。　　Viewed　in　this　light　the　facts
  of　palaeontology　receive　a　meaningupon　any　other　hypothesis；　I　am
  unable　to　see；　in　the　slightest　degree；　what　knowledge　or　signification
  we　are　to　draw　out　of　them。　　Again；　note　as　bearing　upon　the　same
  point；　the　singular　likeness　which　obtains　between　the　successive
  Faunae　and　Florae；　whose　remains　are　preserved　on　the　rocks：　you　never
  find　any　great　and　enormous　difference　between　the　immediately
  successive　Faunae　and　Florae；　unless　you　have　reason　to　believe　there
  has　also　been　a　great　lapse　of　time　or　a　great　change　of　conditions。
  The　animals；　for　instance；　of　the　newest　tertiary　rocks；　in　any　part　of
  the　world；　are　always；　and　without　exception；　found　to　be　closely
  allied　with　those　which　now　live　in　that　part　of　the　world。　　For
  example；　in　Europe；　Asia；　and　Africa；　the　large　mammals　are　at　present
  rhinoceroses；　hippopotamuses；　elephants；　lions；　tigers；　oxen；　hor