animals；　or　to　the　soil　being　occasionally　manured　by　the　droppings
  from　animals；　I　do　not　know。　｛9｝　　On　such　grassy　paths　worm…
  castings　may　often　be　seen。　　On　a　heath　in　Surrey；　which　was
  carefully　examined；　there　were　only　a　few　castings　on　these　paths；
  where　they　were　much　inclined；　but　on　the　more　level　parts；　where　a
  bed　of　fine　earth　had　been　washed　down　from　the　steeper　parts　and
  had　accumulated　to　a　thickness　of　a　few　inches；　worm…castings
  abounded。　　These　spots　seemed　to　be　overstocked　with　worms；　so　that
  they　had　been　compelled　to　spread　to　a　distance　of　a　few　feet　from
  the　grassy　paths；　and　here　their　castings　had　been　thrown　up　among
  the　heath；　but　beyond　this　limit；　not　a　single　casting　could　be
  found。　　A　layer；　though　a　thin　one；　of　fine　earth；　which　probably
  long　retains　some　moisture；　is　in　all　cases；　as　I　believe；
  necessary　for　their　existence；　and　the　mere　compression　of　the　soil
  appears　to　be　in　some　degree　favourable　to　them；　for　they　often
  abound　in　old　gravel　walks；　and　in　foot…paths　across　fields。
  Beneath　large　trees　few　castings　can　be　found　during　certain
  seasons　of　the　year；　and　this　is　apparently　due　to　the　moisture
  having　been　sucked　out　of　the　ground　by　the　innumerable　roots　of
  the　trees；　for　such　places　may　be　seen　covered　with　castings　after
  the　heavy　autumnal　rains。　　Although　most　coppices　and　woods　support
  many　worms；　yet　in　a　forest　of　tall　and　ancient　beech…trees　in
  Knole　Park；　where　the　ground　beneath　was　bare　of　all　vegetation；
  not　a　single　casting　could　be　found　over　wide　spaces；　even　during
  the　autumn。　　Nevertheless；　castings　were　abundant　on　some　grass…
  covered　glades　and　indentations　which　penetrated　this　forest。　　On
  the　mountains　of　North　Wales　and　on　the　Alps；　worms；　as　I　have　been
  informed；　are　in　most　places　rare；　and　this　may　perhaps　be　due　to
  the　close　proximity　of　the　subjacent　rocks；　into　which　worms　cannot
  burrow　during　the　winter　so　as　to　escape　being　frozen。　　Dr。
  McIntosh；　however；　found　worm…castings　at　a　height　of　1500　feet　on
  Schiehallion　in　Scotland。　　They　are　numerous　on　some　hills　near
  Turin　at　from　2000　to　3000　feet　above　the　sea；　and　at　a　great
  altitude　on　the　Nilgiri　Mountains　in　South　India　and　on　the
  Himalaya。
  Earth…worms　must　be　considered　as　terrestrial　animals；　though　they
  are　still　in　one　sense　semi…aquatic；　like　the　other　members　of　the
  great　class　of　annelids　to　which　they　belong。　　M。　Perrier　found
  that　their　exposure　to　the　dry　air　of　a　room　for　only　a　single
  night　was　fatal　to　them。　　On　the　other　hand　he　kept　several　large
  worms　alive　for　nearly　four　months；　completely　submerged　in　water。
  ｛10｝　　During　the　summer　when　the　ground　is　dry；　they　penetrate　to　a
  considerable　depth　and　cease　to　work；　as　they　do　during　the　winter
  when　the　ground　is　frozen。　　Worms　are　nocturnal　in　their　habits；
  and　at　night　may　be　seen　crawling　about　in　large　numbers；　but
  usually　with　their　tails　still　inserted　in　their　burrows。　　By　the
  expansion　of　this　part　of　their　bodies；　and　with　the　help　of　the
  short；　slightly　reflexed　bristles；　with　which　their　bodies　are
  armed；　they　hold　so　fast　that　they　can　seldom　be　dragged　out　of　the
  ground　without　being　torn　into　pieces。　｛11｝　　During　the　day　they
  remain　in　their　burrows；　except　at　the　pairing　season；　when　those
  which　inhabit　adjoining　burrows　expose　the　greater　part　of　their
  bodies　for　an　hour　or　two　in　the　early　morning。　　Sick　individuals；
  which　are　generally　affected　by　the　parasitic　larvae　of　a　fly；　must
  also　be　excepted；　as　they　wander　about　during　the　day　and　die　on
  the　surface。　　After　heavy　rain　succeeding　dry　weather；　an
  astonishing　number　of　dead　worms　may　sometimes　be　seen　lying　on　the
  ground。　　Mr。　Galton　informs　me　that　on　one　such　occasion　（March；
  1881）；　the　dead　worms　averaged　one　for　every　two　and　a　half　paces
  in　length　on　a　walk　in　Hyde　Park；　four　paces　in　width。　　He　counted
  no　less　than　45　dead　worms　in　one　place　in　a　length　of　sixteen
  paces。　　From　the　facts　above　given；　it　is　not　probable　that　these
  worms　could　have　been　drowned；　and　if　they　had　been　drowned　they
  would　have　perished　in　their　burrows。　　I　believe　that　they　were
  already　sick；　and　that　their　deaths　were　merely　hastened　by　the
  ground　being　flooded。
  It　has　often　been　said　that　under　ordinary　circumstances　healthy
  worms　never；　or　very　rarely；　completely　leave　their　burrows　at
  night；　but　this　is　an　error；　as　White　of　Selborne　long　ago　knew。
  In　the　morning；　after　there　has　been　heavy　rain；　the　film　of　mud　or
  of　very　fine　sand　over　gravel…walks　is　often　plainly　marked　with
  their　tracks。　　I　have　noticed　this　from　August　to　May；　both　months
  included；　and　it　probably　occurs　during　the　two　remaining　months　of
  the　year　when　they　are　wet。　　On　these　occasions；　very　few　dead
  worms　could　anywhere　be　seen。　　On　January　31；　1881；　after　a　long…
  continued　and　unusually　severe　frost　with　much　snow；　as　soon　as　a
  thaw　set　in；　the　walks　were　marked　with　innumerable　tracks。　　On　one
  occasion；　five　tracks　were　counted　crossing　a　space　of　only　an　inch
  square。　　They　could　sometimes　be　traced　either　to　or　from　the
  mouths　of　the　burrows　in　the　gravel…walks；　for　distances　between　2
  or　3　up　to　15　yards。　　I　have　never　seen　two　tracks　leading　to　the
  same　burrow；　nor　is　it　likely；　from　what　we　shall　presently　see　of
  their　sense…organs；　that　a　worm　could　find　its　way　back　to　its
  burrow　after　having　once　left　it。　　They　apparently　leave　their
  burrows　on　a　voyage　of　discovery；　and　thus　they　find　new　sites　to
  inhabit。
  Morren　states　｛12｝　that　worms　often　lie　for　hours　almost　motionless
  close　beneath　the　mouths　of　their　burrows。　　I　have　occasionally
  noticed　the　same　fact　with　worms　kept　in　pots　in　the　house；　so　that
  by　looking　down　into　their　burrows；　their　heads　could　just　be　seen。
  If　the　ejected　earth　or　rubbish　over　the　burrows　be　suddenly
  removed；　the　end　of　the　worm's　body　may　very　often　be　seen　rapidly
  retreating。　　This　habit　of　lying　near　the　surface　leads　to　their
  destruction　to　an　immense　extent。　　Every　morning　during　certain
  seasons　of　the　year；　the　thrushes　and　blackbirds　on　all　the　lawns
  throughout　the　country　draw　out　of　their　holes　an　astonishing
  number　of　worms；　and　this　they　could　not　do；　unless　they　lay　close
  to　the　surface。　　It　is　not　probable　that　worms　behave　in　this
  manner　for　the　sake　of　breathing　fresh　air；　for　we　have　seen　that
  they　can　live　for　a　long　time　under　water。　　I　believe　that　they　lie
  near　the　surface　for　the　sake　of　warmth；　especially　in　the　morning；
  and　we　shall　hereafter　find　that　they　often　coat　the　mouths　of
  their　burrows　with　leaves；　apparently　to　prevent　their　bodies　from
  coming　into　close　contact　with　the　cold　damp　earth。　　It　is　said
  that　they　completely　close　their　burrows　during　the　winter。
  Structure。A　few　remarks　must　be　made　on　this　subject。　　The　body
  of　a　large　worm　consists　of　from　100　to　200　almost　cylindrical
  rings　or　segments；　each　furnished　with　minute　bristles。　　The
  muscular　system　is　well　developed。　　Worms　can　crawl　backwards　as
  well　as　forwards；　and　by　the　aid　of　their　affixed　tails　can　retreat
  with　extraordinary　rapidity　into　their　burrows。　　The　mouth　is
  situated　at　the　anterior　end　of　the　body；　and　is　provided　with　a
  little　projection　（lobe　or　lip；　as　it　has　been　variously　called）
  which　is　used　for　prehension。　　Internally；　behind　the　mouth；　there
  is　a　strong　pharynx；　shown　in　the　accompanying　diagram　（Fig。　1）
  which　is　pushed　forwards　when　the　animal　eats；　and　this　part
  corresponds；　according　to　Perrier；　with　the　protrudable　trunk　or
  proboscis　of　other　annelids。　　The　pharynx　leads　into　the
  oesophagus；　on　each　side　of　which　in　the　lower　part　there　are　three
  pairs　of　large　glands；　which　secrete　a　surprising　amount　of
  carbonate　of　lime。　　These　calciferous　glands　are　highly　remarkable；
  for　nothing　like　them　is　known　in　any　other　animal。　　Their　use　will
  be　discussed　when　we　treat　of　the　digestive　process。　　In　most　of
  the　species；　the　oesophagus　is　enlarged　into　a　crop　in　front　of　the
  gizzard。　　This　latter　organ　is　lined　with　a　smooth　thick　chitinous
  membrane；　and　is　surrounded　by　weak　longitudinal；　but　powerful
  transverse　muscles。　　Perrier　saw　these　muscles　in　energetic　action；
  and；　as　he　remarks；　the　trituration　of　the　food　must　be　chiefly
  effected　by　this　organ；　for　worms　possess　no　jaws　or　teeth　of　any
  kind。　　Grains　of　sand　and　small　stones；　from　the　1/20　to　a　little
  more　than　the　1/10　inch　in　diameter；　may　generally　be　found　in
  their　gizzards　and　intestines。　　As　it　is　certain　that　worms　swallow
  many　little　stones；　independently　of　those　swallowed　while
  excavating　their　burrows；　it　is　probable　that　they　serve；　like
  mill…stones；　to　triturate　their　food。　　The　gizzard　opens　into　the
  intestine；　which　runs　in　a　straight　course　to　the　vent　at　the
  posterior　end　of　the　body。　　The　intestine　presents　a　remarkable
  structure；　the　typhlosolis；　or；　as　the　old　anatomists　called　it；　an
  intestine　within　an　intestine；　and　Claparede　｛13｝　has　shown　that
  this　consists　of　a　deep　longitudinal　involution　of　the　walls　of　the
  intestine；　by　which　means　an　extensive　absorbent　surface　is　gained。
  The　circul