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  GEORGK 
  WAGN'ER. 
  

  

  2. 
  Hydra 
  has 
  only 
  one 
  form 
  of 
  response 
  to 
  a 
  sing-le 
  

   mechanical 
  stimulation, 
  localised 
  or 
  non-localised; 
  this 
  re- 
  

   sponse 
  is 
  by 
  contraction, 
  more 
  or 
  less 
  complete, 
  depending 
  

   on 
  the 
  intensity 
  of 
  the 
  stimulus. 
  Such 
  contraction 
  is 
  not 
  

   necessarily 
  toward 
  or 
  away 
  from 
  the 
  stimulus. 
  

  

  3. 
  A 
  non-localised 
  stimulus, 
  repeated 
  as 
  soon 
  as 
  Hydra 
  has 
  

   regained 
  the 
  expanded 
  stage, 
  causes 
  no 
  change 
  in 
  the 
  

   response, 
  contraction 
  resulting 
  after 
  each 
  stimulation. 
  The 
  

   same 
  thing 
  holds 
  true 
  of 
  a 
  localised 
  stimulus 
  applied 
  in 
  a 
  

   similar 
  manner. 
  

  

  4. 
  If 
  a 
  non-localised 
  mechanical 
  stimulus 
  is 
  repeated 
  at 
  

   very 
  brief 
  intervals, 
  say 
  one 
  second, 
  acclimatisation 
  is 
  soon 
  

   affected, 
  and 
  the 
  Hydra 
  no 
  longer 
  responds. 
  

  

  5. 
  A 
  localised 
  stimulus 
  applied 
  at 
  such 
  brief 
  intervals 
  

   brings 
  about 
  at 
  first 
  an 
  apparent 
  acclimatisation. 
  This 
  is 
  

   soon 
  followed 
  in 
  many 
  cases 
  by 
  the 
  complicated 
  " 
  escape 
  " 
  

   movement, 
  the 
  Hydra 
  moving 
  away 
  from 
  the 
  region 
  where 
  

   stimulation 
  occurs. 
  This 
  shows 
  that 
  the 
  physiological 
  

   condition 
  of 
  the 
  animal 
  has 
  been 
  changed, 
  so 
  that 
  to 
  the 
  

   same 
  stimulus 
  under 
  the 
  same 
  external 
  conditions 
  it 
  now 
  

   gives 
  a 
  reaction 
  different 
  from 
  that 
  given 
  at 
  first. 
  

  

  6. 
  Hydra, 
  shows 
  no 
  orientation 
  movements 
  in 
  response 
  to 
  

   stimulation 
  by 
  a 
  current 
  of 
  water. 
  

  

  7. 
  Hydra 
  normally 
  has 
  its 
  foot 
  attached 
  to 
  the 
  sub-stratum. 
  

   If 
  the 
  foot 
  is 
  detached 
  the 
  animal 
  perforins 
  active 
  movements 
  

   directed 
  toward 
  restoring 
  the 
  normal 
  condition. 
  Geotaxis 
  

   plays 
  no 
  part 
  in 
  this 
  reaction. 
  

  

  8. 
  Non-localised 
  chemical 
  stimuli 
  cause 
  general 
  contraction. 
  

   An 
  exception 
  is 
  found 
  in 
  certain 
  food 
  reactions. 
  

  

  9. 
  A 
  strong 
  localised 
  chemical 
  stimulus 
  causes 
  a 
  bendinsr 
  

   of 
  the 
  body 
  or 
  tentacles, 
  as 
  the 
  case 
  may 
  be, 
  toward 
  the 
  side 
  

   stimulated. 
  Such 
  bending 
  is 
  caused 
  by 
  the 
  contraction 
  of 
  

   the 
  ectoderm 
  cells 
  directly 
  affected 
  by 
  the 
  chemical. 
  The. 
  

   result 
  is 
  not 
  adaptive, 
  as 
  it 
  carries 
  the 
  body 
  or 
  tentacles 
  into 
  

   the 
  region 
  where 
  it 
  is 
  most 
  injured. 
  

  

  10. 
  Hydra 
  reacts 
  to 
  food 
  only 
  after 
  a 
  period 
  of 
  hunger. 
  

  

  11. 
  In 
  the 
  presence 
  of 
  a 
  moderate 
  state 
  of 
  huu"-er 
  it 
  

  

  