The　Formation　of　Vegetable　Mould　through　the　action　of　worms　with
  observations　of　their　habits
  by　Charles　Darwin
  INTRODUCTION。
  The　share　which　worms　have　taken　in　the　formation　of　the　layer　of
  vegetable　mould；　which　covers　the　whole　surface　of　the　land　in
  every　moderately　humid　country；　is　the　subject　of　the　present
  volume。　　This　mould　is　generally　of　a　blackish　colour　and　a　few
  inches　in　thickness。　　In　different　districts　it　differs　but　little
  in　appearance；　although　it　may　rest　on　various　subsoils。　　The
  uniform　fineness　of　the　particles　of　which　it　is　composed　is　one　of
  its　chief　characteristic　features；　and　this　may　be　well　observed　in
  any　gravelly　country；　where　a　recently…ploughed　field　immediately
  adjoins　one　which　has　long　remained　undisturbed　for　pasture；　and
  where　the　vegetable　mould　is　exposed　on　the　sides　of　a　ditch　or
  hole。　　The　subject　may　appear　an　insignificant　one；　but　we　shall
  see　that　it　possesses　some　interest；　and　the　maxim　〃de　minimis　non
  curat　lex；〃　does　not　apply　to　science。　　Even　Elie　de　Beaumont；　who
  generally　undervalues　small　agencies　and　their　accumulated　effects；
  remarks：　　｛1｝　〃La　couche　tres…mince　de　la　terre　vegetale　est　un
  monument　d'une　haute　antiquite；　et；　par　le　fait　de　sa　permanence；
  un　objet　digne　d'occuper　le　geologue；　et　capable　de　lui　fournir　des
  remarques　interessantes。〃　　Although　the　superficial　layer　of
  vegetable　mould　as　a　whole　no　doubt　is　of　the　highest　antiquity；
  yet　in　regard　to　its　permanence；　we　shall　hereafter　see　reason　to
  believe　that　its　component　particles　are　in　most　cases　removed　at
  not　a　very　slow　rate；　and　are　replaced　by　others　due　to　the
  disintegration　of　the　underlying　materials。
  As　I　was　led　to　keep　in　my　study　during　many　months　worms　in　pots
  filled　with　earth；　I　became　interested　in　them；　and　wished　to　learn
  how　far　they　acted　consciously；　and　how　much　mental　power　they
  displayed。　　I　was　the　more　desirous　to　learn　something　on　this
  head；　as　few　observations　of　this　kind　have　been　made；　as　far　as　I
  know；　on　animals　so　low　in　the　scale　of　organization　and　so　poorly
  provided　with　sense…organs；　as　are　earth…worms。
  In　the　year　1837；　a　short　paper　was　read　by　me　before　the
  Geological　Society　of　London；　｛2｝　〃On　the　Formation　of　Mould；〃　in
  which　it　was　shown　that　small　fragments　of　burnt　marl；　cinders；
  &c。；　which　had　been　thickly　strewed　over　the　surface　of　several
  meadows；　were　found　after　a　few　years　lying　at　the　depth　of　some
  inches　beneath　the　turf；　but　still　forming　a　layer。　　This　apparent
  sinking　of　superficial　bodies　is　due；　as　was　first　suggested　to　me
  by　Mr。　Wedgwood　of　Maer　Hall　in　Staffordshire；　to　the　large
  quantity　of　fine　earth　continually　brought　up　to　the　surface　by
  worms　in　the　form　of　castings。　　These　castings　are　sooner　or　later
  spread　out　and　cover　up　any　object　left　on　the　surface。　　I　was　thus
  led　to　conclude　that　all　the　vegetable　mould　over　the　whole　country
  has　passed　many　times　through；　and　will　again　pass　many　times
  through；　the　intestinal　canals　of　worms。　　Hence　the　term　〃animal
  mould〃　would　be　in　some　respects　more　appropriate　than　that
  commonly　used　of　〃vegetable　mould。〃
  Ten　years　after　the　publication　of　my　paper；　M。　D'Archiac；
  evidently　influenced　by　the　doctrines　of　Elie　de　Beaumont；　wrote
  about　my　〃singuliere　theorie；〃　and　objected　that　it　could　apply
  only　to　〃les　prairies　basses　et　humides；〃　and　that　〃les　terres
  labourees；　les　bois；　les　prairies　elevees；　n'apportent　aucune
  preuve　a　l'appui　de　cette　maniere　de　voir。〃　｛3｝　　But　M。　D'Archiac
  must　have　thus　argued　from　inner　consciousness　and　not　from
  observation；　for　worms　abound　to　an　extraordinary　degree　in　kitchen
  gardens　where　the　soil　is　continually　worked；　though　in　such　loose
  soil　they　generally　deposit　their　castings　in　any　open　cavities　or
  within　their　old　burrows　instead　of　on　the　surface。　　Hensen
  estimates　that　there　are　about　twice　as　many　worms　in　gardens　as　in
  corn…fields。　｛4｝　　With　respect　to　〃prairies　elevees；〃　I　do　not　know
  how　it　may　be　in　France；　but　nowhere　in　England　have　I　seen　the
  ground　so　thickly　covered　with　castings　as　on　commons；　at　a　height
  of　several　hundred　feet　above　the　sea。　　In　woods　again；　if　the
  loose　leaves　in　autumn　are　removed；　the　whole　surface　will　be　found
  strewed　with　castings。　　Dr。　King；　the　superintendent　of　the　Botanic
  Garden　in　Calcutta；　to　whose　kindness　I　am　indebted　for　many
  observations　on　earth…worms；　informs　me　that　he　found；　near　Nancy
  in　France；　the　bottom　of　the　State　forests　covered　over　many　acres
  with　a　spongy　layer；　composed　of　dead　leaves　and　innumerable　worm…
  castings。　　He　there　heard　the　Professor　of　〃Amenagement　des　Forets〃
  lecturing　to　his　pupils；　and　pointing　out　this　case　as　a　〃beautiful
  example　of　the　natural　cultivation　of　the　soil；　for　year　after　year
  the　thrown…up　castings　cover　the　dead　leaves；　the　result　being　a
  rich　humus　of　great　thickness。〃
  In　the　year　1869；　Mr。　Fish　｛5｝　rejected　my　conclusions　with　respect
  to　the　part　which　worms　have　played　in　the　formation　of　vegetable
  mould；　merely　on　account　of　their　assumed　incapacity　to　do　so　much
  work。　　He　remarks　that　〃considering　their　weakness　and　their　size；
  the　work　they　are　represented　to　have　accomplished　is　stupendous。〃
  Here　we　have　an　instance　of　that　inability　to　sum　up　the　effects　of
  a　continually　recurrent　cause；　which　has　often　retarded　the
  progress　of　science；　as　formerly　in　the　case　of　geology；　and　more
  recently　in　that　of　the　principle　of　evolution。
  Although　these　several　objections　seemed　to　me　to　have　no　weight；
  yet　I　resolved　to　make　more　observations　of　the　same　kind　as　those
  published；　and　to　attack　the　problem　on　another　side；　namely；　to
  weigh　all　the　castings　thrown　up　within　a　given　time　in　a　measured
  space；　instead　of　ascertaining　the　rate　at　which　objects　left　on
  the　surface　were　buried　by　worms。　　But　some　of　my　observations　have
  been　rendered　almost　superfluous　by　an　admirable　paper　by　Hensen；
  already　alluded　to；　which　appeared　in　1877。　｛6｝　　Before　entering　on
  details　with　respect　to　the　castings；　it　will　be　advisable　to　give
  some　account　of　the　habits　of　worms　from　my　own　observations　and
  from　those　of　other　naturalists。
  ＇FIRST　EDITION；　October　10th；　1881。＇
  CHAPTER　IHABITS　OF　WORMS。
  Nature　of　the　sites　inhabitedCan　live　long　under　water
  NocturnalWander　about　at　nightOften　lie　close　to　the　mouths　of
  their　burrows；　and　are　thus　destroyed　in　large　numbers　by　birds
  StructureDo　not　possess　eyes；　but　can　distinguish　between　light
  and　darknessRetreat　rapidly　when　brightly　illuminated；　not　by　a
  reflex　actionPower　of　attentionSensitive　to　heat　and　cold
  Completely　deafSensitive　to　vibrations　and　to　touchFeeble　power
  of　smellTasteMental　qualitiesNature　of　foodOmnivorous
  DigestionLeaves　before　being　swallowed；　moistened　with　a　fluid　of
  the　nature　of　the　pancreatic　secretionExtra…stomachal　digestion
  Calciferous　glands；　structure　ofCalcareous　concretions　formed　in
  the　anterior　pair　of　glandsThe　calcareous　matter　primarily　an
  excretion；　but　secondarily　serves　to　neutralise　the　acids　generated
  during　the　digestive　process。
  Earth…worms　are　distributed　throughout　the　world　under　the　form　of
  a　few　genera；　which　externally　are　closely　similar　to　one　another。
  The　British　species　of　Lumbricus　have　never　been　carefully
  monographed；　but　we　may　judge　of　their　probable　number　from　those
  inhabiting　neighbouring　countries。　　In　Scandinavia　there　are　eight
  species；　according　to　Eisen；　｛7｝　but　two　of　these　rarely　burrow　in
  the　ground；　and　one　inhabits　very　wet　places　or　even　lives　under
  the　water。　　We　are　here　concerned　only　with　the　kinds　which　bring
  up　earth　to　the　surface　in　the　form　of　castings。　　Hoffmeister　says
  that　the　species　in　Germany　are　not　well　known；　but　gives　the　same
  number　as　Eisen；　together　with　some　strongly　marked　varieties。　｛8｝
  Earth…worms　abound　in　England　in　many　different　stations。　　Their
  castings　may　be　seen　in　extraordinary　numbers　on　commons　and　chalk…
  downs；　so　as　almost　to　cover　the　whole　surface；　where　the　soil　is
  poor　and　the　grass　short　and　thin。　　But　they　are　almost　or　quite　as
  numerous　in　some　of　the　London　parks；　where　the　grass　grows　well
  and　the　soil　appears　rich。　　Even　on　the　same　field　worms　are　much
  more　frequent　in　some　places　than　in　others；　without　any　visible
  difference　in　the　nature　of　the　soil。　　They　abound　in　paved　court…
  yards　close　to　houses；　and　an　instance　will　be　given　in　which　they
  had　burrowed　through　the　floor　of　a　very　damp　cellar。　　I　have　seen
  worms　in　black　peat　in　a　boggy　field；　but　they　are　extremely　rare；
  or　quite　absent　in　the　drier；　brown；　fibrous　peat；　which　is　so　much
  valued　by　gardeners。　　On　dry；　sandy　or　gravelly　tracks；　where　heath
  with　some　gorse；　ferns；　coarse　grass；　moss　and　lichens　alone　grow；
  hardly　any　worms　can　be　found。　　But　in　many　parts　of　England；
  wherever　a　path　crosses　a　heath；　its　surface　becomes　covered　with　a
  fine　short　sward。　　Whether　this　change　of　vegetation　is　due　to　the
  taller　plants　being　killed　by　the　occasional　trampling　of　man　and
  animals；　or　to　the　soil　being　occasionally　manured　by　t