﻿596 
  GEORGE 
  WAGNER. 
  

  

  to 
  external 
  stimuli. 
  I 
  have 
  already 
  stated 
  that 
  this 
  is 
  not 
  the 
  

   case 
  as 
  regards 
  mechanical 
  stimuli. 
  

  

  So 
  far 
  I 
  have 
  spoken 
  chiefly 
  of 
  stimulation 
  of 
  the 
  tentacles. 
  

   It 
  is 
  also 
  possible 
  by 
  careful 
  slight 
  stimulation 
  on 
  the 
  body 
  to 
  

   cause 
  the 
  latter 
  to 
  contract 
  without 
  contraction 
  of 
  the 
  tentacles. 
  

   It 
  is 
  not, 
  however, 
  so 
  frequent 
  a 
  result 
  as 
  contraction 
  of 
  the 
  

   tentacles 
  without 
  contraction 
  of 
  the 
  body. 
  This 
  is 
  for 
  the 
  

   reason, 
  as 
  far 
  as 
  I 
  can 
  make 
  out, 
  that 
  the 
  violent 
  contractions 
  

   of 
  a 
  mass, 
  relatively 
  so 
  large 
  as 
  the 
  body, 
  results 
  in 
  a 
  recoil 
  

   which 
  is 
  often 
  strong 
  enough 
  to 
  affect 
  the 
  tentacles. 
  Their 
  

   conti'action 
  in 
  such 
  a 
  case 
  is 
  caused 
  by 
  this 
  secondaiy 
  stimulus, 
  

   without 
  transmission 
  to 
  them 
  of 
  the 
  primaiy 
  one. 
  

  

  Sometimes 
  the 
  bod}^, 
  after 
  a 
  very 
  slight 
  stimulus, 
  contracts 
  

   only 
  partially, 
  and 
  then 
  immediately 
  expands 
  again. 
  At 
  other 
  

   times, 
  when 
  it 
  contracts 
  completely, 
  the 
  tentacles 
  will 
  remain 
  

   expanded 
  for 
  from 
  twelve 
  to 
  thirty 
  seconds 
  or 
  moi-e 
  and 
  then 
  

   suddenly 
  contract. 
  

  

  In 
  Hydra 
  with 
  buds 
  it 
  is 
  possible 
  to 
  stimulate 
  the 
  body 
  of 
  

   the 
  parent 
  so 
  as 
  to 
  cause 
  its 
  contraction 
  without 
  contraction 
  

   of 
  the 
  bud 
  ; 
  or 
  the 
  bud 
  can 
  be 
  stimulated 
  and 
  caused 
  to 
  

   contract 
  without 
  contraction 
  of 
  the 
  parent. 
  But 
  here 
  also 
  

   the 
  recoil 
  from 
  the 
  contraction 
  of 
  one 
  part 
  interferes 
  with 
  any 
  

   fine 
  gradations 
  in 
  the 
  response. 
  

  

  It 
  is 
  to 
  be 
  noticed 
  that 
  in 
  all 
  these 
  results 
  there 
  is 
  no 
  indi- 
  

   cation 
  of 
  any 
  orientatio7i 
  movement 
  on 
  the 
  part 
  of 
  the 
  Hydra. 
  

   The 
  organism 
  does 
  not 
  move 
  definitely 
  toward 
  or 
  away 
  from 
  

   the 
  soui'ce 
  of 
  stimulation. 
  No 
  matter 
  where 
  the 
  stimulus 
  is 
  

   applied 
  the 
  single 
  response 
  is 
  simply 
  a 
  contraction, 
  partial 
  or 
  

   complete. 
  Now, 
  as 
  the 
  foot 
  is 
  attached 
  to 
  the 
  substratum, 
  it 
  

   definitely 
  fixes 
  the 
  direction 
  in 
  which 
  contraction 
  will 
  move 
  

   the 
  Hydra 
  as 
  a 
  whole. 
  Contraction 
  causes 
  a 
  moving 
  of 
  the 
  

   mass 
  of 
  the 
  Hydra 
  towards 
  the 
  foot. 
  The 
  contraction 
  so 
  

   fixed, 
  there 
  can 
  of 
  course 
  not 
  be 
  any 
  fixed 
  relation 
  between 
  it 
  

   and 
  the 
  place 
  at 
  which 
  the 
  stimulus 
  is 
  applied 
  ; 
  for 
  no 
  matter 
  

   where 
  the 
  stimulus 
  acts, 
  the 
  direction 
  of 
  the 
  contraction 
  is 
  

   always 
  the 
  same. 
  In 
  hundreds 
  of 
  experiments 
  I 
  have 
  not 
  

   seen 
  a 
  single 
  case 
  where 
  Hydra 
  showed 
  any 
  bending 
  either 
  of 
  

  

  