intestine；　by　which　means　an　extensive　absorbent　surface　is　gained。
  The　circulatory　system　is　well　developed。　　Worms　breathe　by　their
  skin；　as　they　do　not　possess　any　special　respiratory　organs。　　The
  two　sexes　are　united　in　the　same　individual；　but　two　individuals
  pair　together。　　The　nervous　system　is　fairly　well　developed；　and
  the　two　almost　confluent　cerebral　ganglia　are　situated　very　near　to
  the　anterior　end　of　the　body。
  Senses。Worms　are　destitute　of　eyes；　and　at　first　I　thought　that
  they　were　quite　insensible　to　light；　for　those　kept　in　confinement
  were　repeatedly　observed　by　the　aid　of　a　candle；　and　others　out　of
  doors　by　the　aid　of　a　lantern；　yet　they　were　rarely　alarmed；
  although　extremely　timid　animals。　　Other　persons　have　found　no
  difficulty　in　observing　worms　at　night　by　the　same　means。　｛14｝
  Hoffmeister；　however；　states　｛15｝　that　worms；　with　the　exception　of
  a　few　individuals；　are　extremely　sensitive　to　light；　but　he　admits
  that　in　most　cases　a　certain　time　is　requisite　for　its　action。
  These　statements　led　me　to　watch　on　many　successive　nights　worms
  kept　in　pots；　which　were　protected　from　currents　of　air　by　means　of
  glass　plates。　　The　pots　were　approached　very　gently；　in　order　that
  no　vibration　of　the　floor　should　be　caused。　　When　under　these
  circumstances　worms　were　illuminated　by　a　bull's…eye　lantern　having
  slides　of　dark　red　and　blue　glass；　which　intercepted　so　much　light
  that　they　could　be　seen　only　with　some　difficulty；　they　were　not　at
  all　affected　by　this　amount　of　light；　however　long　they　were
  exposed　to　it。　　The　light；　as　far　as　I　could　judge；　was　brighter
  than　that　from　the　full　moon。　　Its　colour　apparently　made　no
  difference　in　the　result。　　When　they　were　illuminated　by　a　candle；
  or　even　by　a　bright　paraffin　lamp；　they　were　not　usually　affected
  at　first。　　Nor　were　they　when　the　light　was　alternately　admitted
  and　shut　off。　　Sometimes；　however；　they　behaved　very　differently；
  for　as　soon　as　the　light　fell　on　them；　they　withdrew　into　their
  burrows　with　almost　instantaneous　rapidity。　　This　occurred　perhaps
  once　out　of　a　dozen　times。　　When　they　did　not　withdraw　instantly；
  they　often　raised　the　anterior　tapering　ends　of　their　bodies　from
  the　ground；　as　if　their　attention　was　aroused　or　as　if　surprise　was
  felt；　or　they　moved　their　bodies　from　side　to　side　as　if　feeling
  for　some　object。　　They　appeared　distressed　by　the　light；　but　I
  doubt　whether　this　was　really　the　case；　for　on　two　occasions　after
  withdrawing　slowly；　they　remained　for　a　long　time　with　their
  anterior　extremities　protruding　a　little　from　the　mouths　of　their
  burrows；　in　which　position　they　were　ready　for　instant　and　complete
  withdrawal。
  When　the　light　from　a　candle　was　concentrated　by　means　of　a　large
  lens　on　the　anterior　extremity；　they　generally　withdrew　instantly；
  but　this　concentrated　light　failed　to　act　perhaps　once　out　of　half
  a　dozen　trials。　　The　light　was　on　one　occasion　concentrated　on　a
  worm　lying　beneath　water　in　a　saucer；　and　it　instantly　withdrew
  into　its　burrow。　　In　all　cases　the　duration　of　the　light；　unless
  extremely　feeble；　made　a　great　difference　in　the　result；　for　worms
  left　exposed　before　a　paraffin　lamp　or　a　candle　invariably
  retreated　into　their　burrows　within　from　five　to　fifteen　minutes；
  and　if　in　the　evening　the　pots　were　illuminated　before　the　worms
  had　come　out　of　their　burrows；　they　failed　to　appear。
  From　the　foregoing　facts　it　is　evident　that　light　affects　worms　by
  its　intensity　and　by　its　duration。　　It　is　only　the　anterior
  extremity　of　the　body；　where　the　cerebral　ganglia　lie；　which　is
  affected　by　light；　as　Hoffmeister　asserts；　and　as　I　observed　on
  many　occasions。　　If　this　part　is　shaded；　other　parts　of　the　body
  may　be　fully　illuminated；　and　no　effect　will　be　produced。　　As　these
  animals　have　no　eyes；　we　must　suppose　that　the　light　passes　through
  their　skins；　and　in　some　manner　excites　their　cerebral　ganglia。　　It
  appeared　at　first　probable　that　the　different　manner　in　which　they
  were　affected　on　different　occasions　might　be　explained；　either　by
  the　degree　of　extension　of　their　skin　and　its　consequent
  transparency；　or　by　some　particular　incident　of　the　light；　but　I
  could　discover　no　such　relation。　　One　thing　was　manifest；　namely；
  that　when　worms　were　employed　in　dragging　leaves　into　their　burrows
  or　in　eating　them；　and　even　during　the　short　intervals　whilst　they
  rested　from　their　work；　they　either　did　not　perceive　the　light　or
  were　regardless　of　it；　and　this　occurred　even　when　the　light　was
  concentrated　on　them　through　a　large　lens。　　So；　again；　whilst　they
  are　paired；　they　will　remain　for　an　hour　or　two　out　of　their
  burrows；　fully　exposed　to　the　morning　light；　but　it　appears　from
  what　Hoffmeister　says　that　a　light　will　occasionally　cause　paired
  individuals　to　separate。
  When　a　worm　is　suddenly　illuminated　and　dashes　like　a　rabbit　into
  its　burrowto　use　the　expression　employed　by　a　friendwe　are　at
  first　led　to　look　at　the　action　as　a　reflex　one。　　The　irritation　of
  the　cerebral　ganglia　appears　to　cause　certain　muscles　to　contract
  in　an　inevitable　manner；　independently　of　the　will　or　consciousness
  of　the　animal；　as　if　it　were　an　automaton。　　But　the　different
  effect　which　a　light　produced　on　different　occasions；　and
  especially　the　fact　that　a　worm　when　in　any　way　employed　and　in　the
  intervals　of　such　employment；　whatever　set　of　muscles　and　ganglia
  may　then　have　been　brought　into　play；　is　often　regardless　of　light；
  are　opposed　to　the　view　of　the　sudden　withdrawal　being　a　simple
  reflex　action。　　With　the　higher　animals；　when　close　attention　to
  some　object　leads　to　the　disregard　of　the　impressions　which　other
  objects　must　be　producing　on　them；　we　attribute　this　to　their
  attention　being　then　absorbed；　and　attention　implies　the　presence
  of　a　mind。　　Every　sportsman　knows　that　he　can　approach　animals
  whilst　they　are　grazing；　fighting　or　courting；　much　more　easily
  than　at　other　times。　　The　state；　also；　of　the　nervous　system　of　the
  higher　animals　differs　much　at　different　times；　for　instance；　a
  horse　is　much　more　readily　startled　at　one　time　than　at　another。
  The　comparison　here　implied　between　the　actions　of　one　of　the
  higher　animals　and　of　one　so　low　in　the　scale　as　an　earth…worm；　may
  appear　far…fetched；　for　we　thus　attribute　to　the　worm　attention　and
  some　mental　power；　nevertheless　I　can　see　no　reason　to　doubt　the
  justice　of　the　comparison。
  Although　worms　cannot　be　said　to　possess　the　power　of　vision；　their
  sensitiveness　to　light　enables　them　to　distinguish　between　day　and
  night；　and　they　thus　escape　extreme　danger　from　the　many　diurnal
  animals　which　prey　on　them。　　Their　withdrawal　into　their　burrows
  during　the　day　appears；　however；　to　have　become　an　habitual　action；
  for　worms　kept　in　pots　covered　by　glass　plates；　over　which　sheets
  of　black　paper　were　spread；　and　placed　before　a　north…east　window；
  remained　during　the　day…time　in　their　burrows　and　came　out　every
  night；　and　they　continued　thus　to　act　for　a　week。　　No　doubt　a
  little　light　may　have　entered　between　the　sheets　of　glass　and　the
  blackened　paper；　but　we　know　from　the　trials　with　coloured　glass；
  that　worms　are　indifferent　to　a　small　amount　of　light。
  Worms　appear　to　be　less　sensitive　to　moderate　radiant　heat　than　to
  a　bright　light。　　I　judge　of　this　from　having　held　at　different
  times　a　poker　heated　to　dull　redness　near　some　worms；　at　a　distance
  which　caused　a　very　sensible　degree　of　warmth　in　my　hand。　　One　of
  them　took　no　notice；　a　second　withdrew　into　its　burrow；　but　not
  quickly；　the　third　and　fourth　much　more　quickly；　and　the　fifth　as
  quickly　as　possible。　　The　light　from　a　candle；　concentrated　by　a
  lens　and　passing　through　a　sheet　of　glass　which　would　intercept
  most　of　the　heat…rays；　generally　caused　a　much　more　rapid　retreat
  than　did　the　heated　poker。　　Worms　are　sensitive　to　a　low
  temperature；　as　may　be　inferred　from　their　not　coming　out　of　their
  burrows　during　a　frost。
  Worms　do　not　possess　any　sense　of　hearing。　　They　took　not　the　least
  notice　of　the　shrill　notes　from　a　metal　whistle；　which　was
  repeatedly　sounded　near　them；　nor　did　they　of　the　deepest　and
  loudest　tones　of　a　bassoon。　　They　were　indifferent　to　shouts；　if
  care　was　taken　that　the　breath　did　not　strike　them。　　When　placed　on
  a　table　close　to　the　keys　of　a　piano；　which　was　played　as　loudly　as
  possible；　they　remained　perfectly　quiet。
  Although　they　are　indifferent　to　undulations　in　the　air　audible　by
  us；　they　are　extremely　sensitive　to　vibrations　in　any　solid　object。
  When　the　pots　containing　two　worms　which　had　remained　quite
  indifferent　to　the　sound　of　the　piano；　were　placed　on　this
  instrument；　and　the　note　C　in　the　bass　clef　was　struck；　both
  instantly　retreated　into　their　burrows。　　After　a　time　they　emerged；
  and　when　G　above　the　line　in　the　treble　clef　was　struck　they　again
  retreated。　　Under　similar　circumstances　on　another　night　one　worm
  dashed　into　its　burrow　on　a　very　high　note　being　struck　only　once；
  and　the　other　worm　when　C　in　the　treble　clef　was　struck。　　On　these
  occasions　the　worms　were　not　touching　the　sides　of　the　pots；　which
  stoo