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  ANIMAL 
  BEHAVIOUR 
  

  

  amid 
  a 
  multitude 
  of 
  apparent 
  alternatives, 
  and 
  (2) 
  that 
  it 
  

   is 
  utilised 
  in 
  a 
  fashion 
  which 
  is 
  interpretable 
  as 
  peculiarly 
  

   adaptive. 
  The 
  first 
  point 
  may 
  be 
  illustrated 
  by 
  the 
  case 
  of 
  

   Technitella 
  tliompsoni, 
  which 
  covers 
  itself 
  with 
  minute 
  per- 
  

   forated 
  Echinoderm 
  platelets; 
  the 
  second 
  point 
  by 
  the 
  case 
  

   of 
  Marsipella 
  spiralis, 
  which 
  arranges 
  its 
  encasement 
  of 
  

   sponge-spicules 
  in 
  a 
  spiral, 
  doubtless 
  of 
  considerable 
  archi- 
  

   tectural 
  value. 
  

  

  5. 
  Reflex 
  Actions. 
  

  

  Among 
  simple 
  multicellular 
  animals 
  we 
  find, 
  as 
  among 
  

   the 
  unicellulars, 
  abundant 
  illustrations 
  of 
  exploring, 
  testing, 
  

   and 
  hunting. 
  Perhaps 
  we 
  may 
  recognise 
  more 
  staying 
  power, 
  

   persistence, 
  and 
  momentum, 
  advantages 
  naturally 
  accruing 
  

   from 
  the 
  acquisition 
  of 
  a 
  body. 
  

  

  But 
  the 
  establishment 
  of 
  a 
  nervous 
  system 
  opened 
  the 
  

   way 
  to 
  the 
  organisation 
  of 
  reflex 
  actions, 
  which 
  are 
  the 
  out- 
  

   come 
  of 
  hereditarily 
  prearranged 
  linkages 
  of 
  nerve-cells 
  and 
  

   muscle-cells. 
  These 
  play 
  an 
  important 
  role 
  in 
  behaviour. 
  

   The 
  sea-anemone's 
  tentacles 
  close 
  upon 
  their 
  victim 
  ; 
  the 
  

   nestling's 
  mouth 
  opens 
  at 
  the 
  touch 
  of 
  the 
  food 
  in 
  its 
  mother's 
  

   beak 
  ; 
  the 
  earthworm 
  withdraws 
  into 
  its 
  burrow 
  when 
  it 
  feels 
  

   the 
  tremor 
  of 
  a 
  thrush's 
  footstep 
  ; 
  we 
  cough 
  in 
  spite 
  of 
  

   ourselves 
  when 
  the 
  crumb 
  of 
  bread 
  is 
  going 
  the 
  wrong 
  way, 
  

   and 
  so 
  on. 
  These 
  reflex 
  actions 
  are 
  uniform 
  reactions 
  to 
  

   a 
  particular 
  kind 
  of 
  external 
  or 
  internal 
  stimulus 
  ; 
  they 
  are 
  

   exhibited 
  by 
  all 
  animals 
  of 
  the 
  same 
  kind 
  in 
  approximately 
  

   the 
  same 
  way, 
  though 
  some 
  individuals 
  are 
  quicker 
  than 
  

   others; 
  they 
  are 
  independent 
  of 
  individual 
  experience 
  and 
  

   do 
  not 
  require 
  control 
  on 
  the 
  part 
  of 
  the 
  central 
  nervous 
  

   system; 
  they 
  depend 
  on 
  inborn 
  structural 
  linkages 
  of 
  par- 
  

   ticular 
  sensory 
  and 
  particular 
  motor 
  nerve-units 
  or 
  neurons. 
  

  

  