Bridgman；　and　we　have　seen　that　when　their　attention　is　engaged；
  they　neglect　impressions　to　which　they　would　otherwise　have
  attended；　and　attention　indicates　the　presence　of　a　mind　of　some
  kind。　　They　are　also　much　more　easily　excited　at　certain　times　than
  at　others。　　They　perform　a　few　actions　instinctively；　that　is；　all
  the　individuals；　including　the　young；　perform　such　actions　in
  nearly　the　same　fashion。　　This　is　shown　by　the　manner　in　which　the
  species　of　Perichaeta　eject　their　castings；　so　as　to　construct
  towers；　also　by　the　manner　in　which　the　burrows　of　the　common
  earth…worm　are　smoothly　lined　with　fine　earth　and　often　with　little
  stones；　and　the　mouths　of　their　burrows　with　leaves。　　One　of　their
  strongest　instincts　is　the　plugging　up　the　mouths　of　their　burrows
  with　various　objects；　and　very　young　worms　act　in　this　manner。　　But
  some　degree　of　intelligence　appears；　as　we　shall　see　in　the　next
  chapter；　to　be　exhibited　in　this　work；a　result　which　has
  surprised　me　more　than　anything　else　in　regard　to　worms。
  Food　and　Digestion。Worms　are　omnivorous。　　They　swallow　an
  enormous　quantity　of　earth；　out　of　which　they　extract　any
  digestible　matter　which　it　may　contain；　but　to　this　subject　I　must
  recur。　　They　also　consume　a　large　number　of　half…decayed　leaves　of
  all　kinds；　excepting　a　few　which　have　an　unpleasant　taste　or　are
  too　tough　for　them；　likewise　petioles；　peduncles；　and　decayed
  flowers。　　But　they　will　also　consume　fresh　leaves；　as　I　have　found
  by　repeated　trials。　　According　to　Morren　｛18｝　they　will　eat
  particles　of　sugar　and　liquorice；　and　the　worms　which　I　kept　drew
  many　bits　of　dry　starch　into　their　burrows；　and　a　large　bit　had　its
  angles　well　rounded　by　the　fluid　poured　out　of　their　mouths。　　But
  as　they　often　drag　particles　of　soft　stone；　such　as　of　chalk；　into
  their　burrows；　I　feel　some　doubt　whether　the　starch　was　used　as
  food。　　Pieces　of　raw　and　roasted　meat　were　fixed　several　times　by
  long　pins　to　the　surface　of　the　soil　in　my　pots；　and　night　after
  night　the　worms　could　be　seen　tugging　at　them；　with　the　edges　of
  the　pieces　engulfed　in　their　mouths；　so　that　much　was　consumed。
  Raw　fat　seems　to　be　preferred　even　to　raw　meat　or　to　any　other
  substance　which　was　given　them；　and　much　was　consumed。　　They　are
  cannibals；　for　the　two　halves　of　a　dead　worm　placed　in　two　of　the
  pots　were　dragged　into　the　burrows　and　gnawed；　but　as　far　as　I
  could　judge；　they　prefer　fresh　to　putrid　meat；　and　in　so　far　I
  differ　from　Hoffmeister。
  Leon　Fredericq　states　｛19｝　that　the　digestive　fluid　of　worms　is　of
  the　same　nature　as　the　pancreatic　secretion　of　the　higher　animals；
  and　this　conclusion　agrees　perfectly　with　the　kinds　of　food　which
  worms　consume。　　Pancreatic　juice　emulsifies　fat；　and　we　have　just
  seen　how　greedily　worms　devour　fat；　it　dissolves　fibrin；　and　worms
  eat　raw　meat；　it　converts　starch　into　grape…sugar　with　wonderful
  rapidity；　and　we　shall　presently　show　that　the　digestive　fluid　of
  worms　acts　on　starch。　｛20｝　　But　they　live　chiefly　on　half…decayed
  leaves；　and　these　would　be　useless　to　them　unless　they　could　digest
  the　cellulose　forming　the　cell…walls；　for　it　is　well　known　that　all
  other　nutritious　substances　are　almost　completely　withdrawn　from
  leaves；　shortly　before　they　fall　off。　　It　has；　however；　now　been
  ascertained　that　some　forms　of　cellulose；　though　very　little　or　not
  at　all　attacked　by　the　gastric　secretion　of　the　higher　animals；　are
  acted　on　by　that　from　the　pancreas。　｛21｝
  The　half…decayed　or　fresh　leaves　which　worms　intend　to　devour；　are
  dragged　into　the　mouths　of　their　burrows　to　a　depth　of　from　one　to
  three　inches；　and　are　then　moistened　with　a　secreted　fluid。　　It　has
  been　assumed　that　this　fluid　serves　to　hasten　their　decay；　but　a
  large　number　of　leaves　were　twice　pulled　out　of　the　burrows　of
  worms　and　kept　for　many　weeks　in　a　very　moist　atmosphere　under　a
  bell…glass　in　my　study；　and　the　parts　which　had　been　moistened　by
  the　worms　did　not　decay　more　quickly　in　any　plain　manner　than　the
  other　parts。　　When　fresh　leaves　were　given　in　the　evening　to　worms
  kept　in　confinement　and　examined　early　on　the　next　morning；
  therefore　not　many　hours　after　they　had　been　dragged　into　the
  burrows；　the　fluid　with　which　they　were　moistened；　when　tested　with
  neutral　litmus　paper；　showed　an　alkaline　reaction。　　This　was
  repeatedly　found　to　be　the　case　with　celery；　cabbage　and　turnip
  leaves。　　Parts　of　the　same　leaves　which　had　not　been　moistened　by
  the　worms；　were　pounded　with　a　few　drops　of　distilled　water；　and
  the　juice　thus　extracted　was　not　alkaline。　　Some　leaves；　however；
  which　had　been　drawn　into　burrows　out　of　doors；　at　an　unknown
  antecedent　period；　were　tried；　and　though　still　moist；　they　rarely
  exhibited　even　a　trace　of　alkaline　reaction。
  The　fluid；　with　which　the　leaves　are　bathed；　acts　on　them　whilst
  they　are　fresh　or　nearly　fresh；　in　a　remarkable　manner；　for　it
  quickly　kills　and　discolours　them。　　Thus　the　ends　of　a　fresh
  carrot…leaf；　which　had　been　dragged　into　a　burrow；　were　found　after
  twelve　hours　of　a　dark　brown　tint。　　Leaves　of　celery；　turnip；
  maple；　elm；　lime；　thin　leaves　of　ivy；　and；　occasionally　those　of
  the　cabbage　were　similarly　acted　on。　　The　end　of　a　leaf　of　Triticum
  repens；　still　attached　to　a　growing　plant；　had　been　drawn　into　a
  burrow；　and　this　part　was　dark　brown　and　dead；　whilst　the　rest　of
  the　leaf　was　fresh　and　green。　　Several　leaves　of　lime　and　elm
  removed　from　burrows　out　of　doors　were　found　affected　in　different
  degrees。　　The　first　change　appears　to　be　that　the　veins　become　of　a
  dull　reddish…orange。　　The　cells　with　chlorophyll　next　lose　more　or
  less　completely　their　green　colour；　and　their　contents　finally
  become　brown。　　The　parts　thus　affected　often　appeared　almost　black
  by　reflected　light；　but　when　viewed　as　a　transparent　object　under
  the　microscope；　minute　specks　of　light　were　transmitted；　and　this
  was　not　the　case　with　the　unaffected　parts　of　the　same　leaves。
  These　effects；　however；　merely　show　that　the　secreted　fluid　is
  highly　injurious　or　poisonous　to　leaves；　for　nearly　the　same
  effects　were　produced　in　from　one　to　two　days　on　various　kinds　of
  young　leaves；　not　only　by　artificial　pancreatic　fluid；　prepared
  with　or　without　thymol；　but　quickly　by　a　solution　of　thymol　by
  itself。　　On　one　occasion　leaves　of　Corylus　were　much　discoloured　by
  being　kept　for　eighteen　hours　in　pancreatic　fluid；　without　any
  thymol。　　With　young　and　tender　leaves　immersion　in　human　saliva
  during　rather　warm　weather；　acted　in　the　same　manner　as　the
  pancreatic　fluid；　but　not　so　quickly。　　The　leaves　in　all　these
  cases　often　became　infiltrated　with　the　fluid。
  Large　leaves　from　an　ivy　plant　growing　on　a　wall　were　so　tough　that
  they　could　not　be　gnawed　by　worms；　but　after　four　days　they　were
  affected　in　a　peculiar　manner　by　the　secretion　poured　out　of　their
  mouths。　　The　upper　surfaces　of　the　leaves；　over　which　the　worms　had
  crawled；　as　was　shown　by　the　dirt　left　on　them；　were　marked　in
  sinuous　lines；　by　either　a　continuous　or　broken　chain　of　whitish
  and　often　star…shaped　dots；　about　2　mm。　in　diameter。　　The
  appearance　thus　presented　was　curiously　like　that　of　a　leaf；　into
  which　the　larva　of　some　minute　insect　had　burrowed。　　But　my　son
  Francis；　after　making　and　examining　sections；　could　nowhere　find
  that　the　cell…walls　had　been　broken　down　or　that　the　epidermis　had
  been　penetrated。　　When　the　section　passed　through　the　whitish　dots；
  the　grains　of　chlorophyll　were　seen　to　be　more　or　less　discoloured；
  and　some　of　the　palisade　and　mesophyll　cells　contained　nothing　but
  broken　down　granular　matter。　　These　effects　must　be　attributed　to
  the　transudation　of　the　secretion　through　the　epidermis　into　the
  cells。
  The　secretion　with　which　worms　moisten　leaves　likewise　acts　on　the
  starch…granules　within　the　cells。　　My　son　examined　some　leaves　of
  the　ash　and　many　of　the　lime；　which　had　fallen　off　the　trees　and
  had　been　partly　dragged　into　worm…burrows。　　It　is　known　that　with
  fallen　leaves　the　starch…grains　are　preserved　in　the　guard…cells　of
  the　stomata。　　Now　in　several　cases　the　starch　had　partially　or
  wholly　disappeared　from　these　cells；　in　the　parts　which　had　been
  moistened　by　the　secretion；　while　it　was　still　well　preserved　in
  the　other　parts　of　the　same　leaves。　　Sometimes　the　starch　was
  dissolved　out　of　only　one　of　the　two　guard…cells。　　The　nucleus　in
  one　case　had　disappeared；　together　with　the　starch…granules。　　The
  mere　burying　of　lime…leaves　in　damp　earth　for　nine　days　did　not
  cause　the　destruction　of　the　starch…granules。　　On　the　other　hand；
  the　immersion　of　fresh　lime　and　cherry　leaves　for　eighteen　hours　in
  artificial　pancreatic　fluid；　led　to　the　dissolution　of　the　starch…
  granules　in　the　guard…cells　as　well　as　in　the　other　cells。
  From　the　secretion　with　which　the　leaves　are　moistened　being
  alkaline；　and　from　its　acting　both　on　the　starch…granules　and　on
  the　protoplasmic　contents　of　the　cells；　we　may　infer　that　it
  resembles　in　nature　not　saliva；　｛22｝　but　pancreatic　secretion；　and
  we　know　from　Fredericq　that　a　secretion　of　this　kind　is　found　in
  the　intestines　of　worms。　　As　the