with　their　respiration　which　is　effected　by　the　skin　alone。
  A　worm　after　swallowing　earth；　whether　for　making　its　burrow　or　for
  food；　soon　comes　to　the　surface　to　empty　its　body。　　The　ejected
  earth　is　thoroughly　mingled　with　the　intestinal　secretions；　and　is
  thus　rendered　viscid。　　After　being　dried　it　sets　hard。　　I　have
  watched　worms　during　the　act　of　ejection；　and　when　the　earth　was　in
  a　very　liquid　state　it　was　ejected　in　little　spurts；　and　by　a　slow
  peristaltic　movement　when　not　so　liquid。　　It　is　not　cast
  indifferently　on　any　side；　but　with　some　care；　first　on　one　and
  then　on　another　side；　the　tail　being　used　almost　like　a　trowel。
  When　a　worm　comes　to　the　surface　to　eject　earth；　the　tail
  protrudes；　but　when　it　collects　leaves　its　head　must　protrude。
  Worms　therefore　must　have　the　power　of　turning　round　in　their
  closely…fitting　burrows；　and　this；　as　it　appears　to　us；　would　be　a
  difficult　feat。　　As　soon　as　a　little　heap　has　been　formed；　the　worm
  apparently　avoids；　for　the　sake　of　safety；　protruding　its　tail；　and
  the　earthy　matter　is　forced　up　through　the　previously　deposited
  soft　mass。　　The　mouth　of　the　same　burrow　is　used　for　this　purpose
  for　a　considerable　time。　　In　the　case　of　the　tower…like　castings
  （see　Fig。　2）　near　Nice；　and　of　the　similar　but　still　taller　towers
  from　Bengal　（hereafter　to　be　described　and　figured）；　a　considerable
  degree　of　skill　is　exhibited　in　their　construction。　　Dr。　King　also
  observed　that　the　passage　up　these　towers　hardly　ever　ran　in　the
  same　exact　line　with　the　underlying　burrow；　so　that　a　thin
  cylindrical　object　such　as　a　haulm　of　grass；　could　not　be　passed
  down　the　tower　into　the　burrow；　and　this　change　of　direction
  probably　serves　in　some　manner　as　a　protection。
  Worms　do　not　always　eject　their　castings　on　the　surface　of　the
  ground。　　When　they　can　find　any　cavity；　as　when　burrowing　in　newly
  turned…up　earth；　or　between　the　stems　of　banked…up　plants；　they
  deposit　their　castings　in　such　places。　　So　again　any　hollow　beneath
  a　large　stone　lying　on　the　surface　of　the　ground；　is　soon　filled　up
  with　their　castings。　　According　to　Hensen；　old　burrows　are
  habitually　used　for　this　purpose；　but　as　far　as　my　experience
  serves；　this　is　not　the　case；　excepting　with　those　near　the　surface
  in　recently　dug　ground。　　I　think　that　Hensen　may　have　been　deceived
  by　the　walls　of　old　burrows；　lined　with　black　earth；　having　sunk　in
  or　collapsed；　for　black　streaks　are　thus　left；　and　these　are
  conspicuous　when　passing　through　light…coloured　soil；　and　might　be
  mistaken　for　completely　filled…up　burrows。
  It　is　certain　that　old　burrows　collapse　in　the　course　of　time；　for
  as　we　shall　see　in　the　next　chapter；　the　fine　earth　voided　by
  worms；　if　spread　out　uniformly；　would　form　in　many　places　in　the
  course　of　a　year　a　layer　0。2　of　an　inch　in　thickness；　so　that　at
  any　rate　this　large　amount　is　not　deposited　within　the　old　unused
  burrows。　　If　the　burrows　did　not　collapse；　the　whole　ground　would
  be　first　thickly　riddled　with　holes　to　a　depth　of　about　ten　inches；
  and　in　fifty　years　a　hollow　unsupported　space；　ten　inches　in　depth；
  would　be　left。　　The　holes　left　by　the　decay　of　successively　formed
  roots　of　trees　and　plants　must　likewise　collapse　in　the　course　of
  time。
  The　burrows　of　worms　run　down　perpendicularly　or　a　little
  obliquely；　and　where　the　soil　is　at　all　argillaceous；　there　is　no
  difficulty　in　believing　that　the　walls　would　slowly　flow　or　slide
  inwards　during　very　wet　weather。　　When；　however；　the　soil　is　sandy
  or　mingled　with　many　small　stones；　it　can　hardly　be　viscous　enough
  to　flow　inwards　during　even　the　wettest　weather；　but　another　agency
  may　here　come　into　play。　　After　much　rain　the　ground　swells；　and　as
  it　cannot　expand　laterally；　the　surface　rises；　during　dry　weather
  it　sinks　again。　　For　instance；　a　large　flat　stone　laid　on　the
  surface　of　a　field　sank　3。33　mm。　whilst　the　weather　was　dry　between
  May　9th　and　June　13th；　and　rose　1。91　mm；　between　September　7th　and
  19th　of　the　same　year；　much　rain　having　fallen　during　the　latter
  part　of　this　time。　　During　frosts　and　thaws　the　movements　were
  twice　as　great。　　These　observations　were　made　by　my　son　Horace；　who
  will　hereafter　publish　an　account　of　the　movements　of　this　stone
  during　successive　wet　and　dry　seasons；　and　of　the　effects　of　its
  being　undermined　by　worms。　　Now　when　the　ground　swells；　if　it　be
  penetrated　by　cylindrical　holes；　such　as　worm…burrows；　their　walls
  will　tend　to　yield　and　be　pressed　inwards；　and　the　yielding　will　be
  greater　in　the　deeper　parts　（supposing　the　whole　to　be　equally
  moistened）　from　the　greater　weight　of　the　superincumbent　soil　which
  has　to　be　raised；　than　in　the　parts　near　the　surface。　　When　the
  ground　dries；　the　walls　will　shrink　a　little　and　the　burrows　will
  be　a　little　enlarged。　　Their　enlargement；　however；　through　the
  lateral　contraction　of　the　ground；　will　not　be　favoured；　but　rather
  opposed；　by　the　weight　of　the　superincumbent　soil。
  Distribution　of　Worms。Earth…worms　are　found　in　all　parts　of　the
  world；　and　some　of　the　genera　have　an　enormous　range。　｛41｝　　They
  inhabit　the　most　isolated　islands；　they　abound　in　Iceland；　and　are
  known　to　exist　in　the　West　Indies；　St。　Helena；　Madagascar；　New
  Caledonia　and　Tahiti。　　In　the　Antarctic　regions；　worms　from
  Kerguelen　Land　have　been　described　by　Ray　Lankester；　and　I　found
  them　in　the　Falkland　Islands。　　How　they　reach　such　isolated　islands
  is　at　present　quite　unknown。　　They　are　easily　killed　by　salt…water；
  and　it　does　not　appear　probable　that　young　worms　or　their　egg…
  capsules　could　be　carried　in　earth　adhering　to　the　feet　or　beaks　of
  land…birds。　　Moreover　Kerguelen　Land　is　not　now　inhabited　by　any
  land…bird。
  In　this　volume　we　are　chiefly　concerned　with　the　earth　cast　up　by
  worms；　and　I　have　gleaned　a　few　facts　on　this　subject　with　respect
  to　distant　lands。　　Worms　throw　up　plenty　of　castings　in　the　United
  States。　　In　Venezuela；　castings；　probably　ejected　by　species　of
  Urochaeta；　are　common　in　the　gardens　and　fields；　but　not　in　the
  forests；　as　I　hear　from　Dr。　Ernst　of　Caracas。　　He　collected　156
  castings　from　the　court…yard　of　his　house；　having　an　area　of　200
  square　yards。　　They　varied　in　bulk　from　half　a　cubic　centimeter　to
  five　cubic　centimeters；　and　were　on　an　average　three　cubic
  centimeters。　　They　were；　therefore；　of　small　size　in　comparison
  with　those　often　found　in　England；　for　six　large　castings　from　a
  field　near　my　house　averaged　16　cubic　centimeters。　　Several　species
  of　earth…worms　are　common　in　St。　Catharina　in　South　Brazil；　and
  Fritz　Muller　informs　me　〃that　in　most　parts　of　the　forests　and
  pasture…lands；　the　whole　soil；　to　a　depth　of　a　quarter　of　a　metre；
  looks　as　if　it　had　passed　repeatedly　through　the　intestines　of
  earth…worms；　even　where　hardly　any　castings　are　to　be　seen　on　the
  surface。〃　　A　gigantic　but　very　rare　species　is　found　there；　the
  burrows　of　which　are　sometimes　even　two　centimeters　or　nearly　0。8
  of　an　inch　in　diameter；　and　which　apparently　penetrate　the　ground
  to　a　great　depth。
  In　the　dry　climate　of　New　South　Wales；　I　hardly　expected　that　worms
  would　be　common；　but　Dr。　G。　Krefft　of　Sydney；　to　whom　I　applied；
  after　making　inquiries　from　gardeners　and　others；　and　from　his　own
  observations；　informs　me　that　their　castings　abound。　　He　sent　me
  some　collected　after　heavy　rain；　and　they　consisted　of　little
  pellets；　about　0。15　inch　in　diameter；　and　the　blackened　sandy　earth
  of　which　they　were　formed　still　cohered　with　considerable　tenacity。
  The　late　Mr。　John　Scott　of　the　Botanic　Gardens　near　Calcutta　made
  many　observations　for　me　on　worms　living　under　the　hot　and　humid
  climate　of　Bengal。　　The　castings　abound　almost　everywhere；　in
  jungles　and　in　the　open　ground；　to　a　greater　degree；　as　he　thinks；
  than　in　England。　　After　the　water　has　subsided　from　the　flooded
  rice…fields；　the　whole　surface　very　soon　becomes　studded　with
  castingsa　fact　which　much　surprised　Mr。　Scott；　as　he　did　not　know
  how　long　worms　could　survive　beneath　water。　　They　cause　much
  trouble　in　the　Botanic　garden；　〃for　some　of　the　finest　of　our　lawns
  can　be　kept　in　anything　like　order　only　by　being　almost　daily
  rolled；　if　left　undisturbed　for　a　few　days　they　become　studded　with
  large　castings。〃　　These　closely　resemble　those　described　as
  abounding　near　Nice；　and　they　are　probably　the　work　of　a　species　of
  Perichaeta。　　They　stand　up　like　towers；　with　an　open　passage　in　the
  centre。
  A　figure　of　one　of　these　castings　from　a　photograph　is　here　given
  （Fig。　3）。　　The　largest　received　by　me　was　3。5　inches　in　height　and
  1。35　inch　in　diameter；　another　was　only　0。75　inch　in　diameter　and
  2。75　in　height。　　In　the　following　year；　Mr。　Scott　measured　several
  of　the　largest；　one　was　6　inches　in　height　and　nearly　1。5　in
  diameter：　　two　others　were　5　inches　in　height　and　respectively　2
  and　rather　more　than　2。5　inches　in　diameter。　　The　average　weight　of
  the　22　castings　sent　to　me　was　35　grammes　（1。25　oz。）；　and　one　of
  them　weighed　44。8　grammes　（or　2　oz。）。　All　these　castings　were
  thrown　up　either　in　one　night　or　in　two。　　Where　the　ground　in
  Bengal　is　dry；　as　under　large　trees；　casting