﻿ON 
  SOME 
  MOVEMENTS 
  AND 
  REACTIONS 
  OE 
  HYDIJA. 
  599 
  

  

  lation 
  at 
  longer 
  intervals 
  does 
  not^ 
  therefore^ 
  cause 
  any 
  change 
  

   in 
  tlie 
  reaction. 
  In 
  other 
  words, 
  we 
  do 
  not 
  here 
  see 
  any 
  

   evidence 
  of 
  acclimatisation 
  or 
  memory. 
  

  

  A 
  second 
  method 
  of 
  studying 
  the 
  effects 
  of 
  repeated 
  stimu- 
  

   lation 
  varied 
  from 
  the 
  first 
  only 
  in 
  the 
  length 
  of 
  the 
  interval 
  

   between 
  stimuli. 
  Instead 
  of 
  allowing 
  the 
  Hydra 
  to 
  expand 
  

   after 
  each 
  stimulation 
  the 
  stimulus 
  was 
  applied 
  at 
  intervals 
  of 
  

   about 
  one 
  second. 
  There 
  results 
  of 
  course 
  a 
  contraction. 
  

   The 
  Hydra 
  remains 
  contracted 
  for 
  from 
  one 
  half 
  to 
  one 
  

   minute. 
  Then, 
  in 
  spite 
  of 
  continued 
  stimulation, 
  it 
  slowly 
  

   expands, 
  and 
  does 
  not 
  again 
  contract 
  unless, 
  as 
  often 
  happens, 
  

   the 
  intensity 
  of 
  the 
  stimulus 
  is 
  accidentally 
  increased. 
  If, 
  

   on 
  the 
  other 
  hand, 
  the 
  blows 
  are 
  kept 
  up 
  without 
  any 
  increase 
  

   in 
  intensity, 
  one 
  of 
  two 
  things 
  happens 
  : 
  

  

  (1) 
  In 
  many 
  cases 
  the 
  Hydra 
  now 
  acts 
  as 
  if 
  no 
  stimulation 
  

   were 
  present; 
  it 
  entirely 
  ignores 
  the 
  blows 
  of 
  the 
  rod. 
  

  

  (2) 
  In 
  a 
  minority 
  of 
  cases 
  the 
  result 
  is 
  decidedly 
  different. 
  

   The 
  Hydra 
  slowly 
  bends 
  its 
  body 
  to 
  one 
  side 
  until 
  its 
  expanded 
  

   tentacles 
  touch 
  the 
  glass 
  at 
  some 
  distance 
  from 
  the 
  foot. 
  They 
  

   then 
  attach 
  themselves 
  and 
  contract. 
  The 
  foot 
  loosens 
  its 
  

   hold, 
  and 
  the 
  body 
  of 
  the 
  Hydra 
  contracts. 
  But 
  the 
  body 
  

   immediately 
  re-expands 
  and 
  bends 
  over, 
  until 
  the 
  foot 
  touches 
  

   the 
  glass 
  close 
  beside 
  the 
  tentacles. 
  The 
  foot 
  now 
  reattached 
  

   itself, 
  the 
  tentacles 
  loosen 
  their 
  hold, 
  and 
  the 
  body 
  straightens 
  

   out. 
  The 
  Hydra 
  thus 
  again 
  occupies 
  its 
  normal 
  position, 
  but 
  at 
  

   some 
  distance 
  from 
  the 
  place 
  where 
  it 
  was 
  subject 
  to 
  stimula- 
  

   tion. 
  Its 
  further 
  movements 
  are 
  those 
  of 
  a 
  normal 
  Hydra. 
  As 
  

   to 
  the 
  direction 
  towards 
  which 
  Hydra 
  travels 
  in 
  the 
  ''escape," 
  

   it 
  has 
  again 
  no 
  relation 
  to 
  the 
  direction 
  from 
  which 
  stimu- 
  

   lation 
  comes. 
  To 
  resort 
  again 
  to 
  the 
  points 
  of 
  the 
  compass 
  

   as 
  convenient 
  symbols 
  of 
  direction 
  let 
  us 
  suppose 
  the 
  glass 
  

   rod 
  to 
  stimulate 
  the 
  Hydra 
  on 
  the 
  west 
  side. 
  I 
  have 
  seen 
  

   such 
  a 
  Hydra 
  escape 
  toward 
  the 
  east. 
  But 
  I 
  have 
  seen 
  others 
  

   escape 
  in 
  almost 
  all 
  of 
  the 
  other 
  directions. 
  Some 
  even 
  bent 
  

   toward 
  the 
  Avest, 
  over 
  the 
  rod 
  that 
  stimulated 
  them, 
  and 
  

   escaped 
  in 
  that 
  direction. 
  Here 
  again, 
  therefore, 
  we 
  have 
  in 
  

   no 
  sense 
  an 
  orientation. 
  

  

  