﻿ON 
  SOME 
  MOVEMENTS 
  AND 
  REACTIONS 
  OF 
  HYDRA. 
  619 
  

  

  over 
  the 
  ai-ea 
  directly 
  touched 
  by 
  the 
  stain-cloud 
  were 
  stained 
  

   green, 
  and 
  that 
  nematocyts 
  were 
  discharged 
  only 
  over 
  the 
  

   area 
  so 
  stained. 
  

  

  Similar 
  results 
  are 
  obtained 
  by 
  experimenting 
  with 
  tenta- 
  

   cles 
  cut 
  off 
  from 
  the 
  body. 
  A 
  tentacle 
  can 
  thus 
  be 
  cat 
  at 
  

   any 
  place 
  without 
  causing 
  any 
  gi-eat 
  discharge 
  of 
  nematocysts. 
  

   If 
  such 
  a 
  tentacle 
  is 
  then 
  stimulated 
  with 
  methyl 
  green 
  it 
  

   will 
  discharge 
  nematocysts 
  profusely, 
  just 
  as 
  it 
  would 
  have 
  

   done 
  had 
  it 
  remained 
  attached 
  to 
  the 
  body. 
  The 
  discharge 
  

   is 
  restricted 
  absolutely 
  to 
  the 
  region 
  touched 
  by 
  the 
  solution 
  

   of 
  the 
  chemical. 
  

  

  The 
  discharge 
  of 
  nematocysts 
  depends 
  then 
  entirely 
  upon 
  

   chemical 
  stimulation. 
  The 
  action 
  of 
  the 
  stimulus 
  is 
  probably 
  a 
  

   very 
  direct 
  one 
  on 
  the 
  protoplasm 
  of 
  the 
  cnidoblast, 
  for 
  if 
  

   there 
  were 
  involved 
  a 
  nervous 
  mechanism 
  of 
  such 
  complexity 
  

   as 
  Chun 
  (I.e.) 
  supposes, 
  we 
  could 
  reasonably 
  expect 
  the 
  dis- 
  

   charge 
  to 
  reach 
  beyond 
  so 
  strictly 
  limited 
  an 
  area. 
  It 
  is 
  also 
  

   obvious 
  that 
  the 
  cnidocil 
  can 
  only 
  serve 
  a 
  sensory 
  function, 
  

   as 
  was 
  suggested 
  by 
  Schneider 
  ('90). 
  The 
  results 
  with 
  

   isolated 
  tentacles 
  certainly 
  dispose 
  of 
  v. 
  Lendenfeld's 
  theory 
  

   of 
  the 
  discharge 
  as 
  controlled 
  by 
  the 
  will 
  of 
  the 
  animal. 
  

  

  To 
  ray 
  teacher 
  and 
  friend. 
  Professor 
  H. 
  S. 
  Jennings, 
  I 
  am 
  

   deeply 
  indebted 
  for 
  constant 
  aid 
  and 
  encouragement 
  in 
  this 
  

   work. 
  It 
  was 
  undertaken 
  at 
  his 
  suggestion 
  and 
  carried 
  out 
  

   in 
  his 
  laboratory. 
  To 
  Professor 
  Reighard 
  I 
  am 
  grateful 
  for 
  

   more 
  than 
  ordinary 
  courtesies 
  extended 
  to 
  me 
  while 
  in 
  the 
  

   laboratories 
  in 
  his 
  charg-e. 
  

  

  Summary. 
  

  

  The 
  principal 
  points 
  that 
  I 
  have 
  attempted 
  to 
  bring 
  out 
  

   in 
  this 
  paper 
  are 
  : 
  

  

  1. 
  An 
  undisturbed 
  Hydra 
  does 
  not 
  remain 
  motionless, 
  but 
  

   contracts 
  at 
  fairly 
  regular 
  intervals. 
  After 
  contraction 
  it 
  

   expands 
  in 
  such 
  a 
  way 
  as 
  to 
  occupy 
  a 
  different 
  position 
  from 
  

   that 
  previously 
  occupied. 
  

  

  