﻿ON 
  SOME 
  MOVEMENTS 
  AND 
  REACTrONS 
  OP 
  HYDRA. 
  589 
  

  

  When 
  one 
  observes 
  Hydra 
  (again 
  especially 
  Hydra 
  v 
  i 
  r 
  i 
  d 
  i 
  s) 
  

   for 
  a 
  longer 
  time 
  one 
  is 
  impressed 
  with 
  the 
  fact 
  that 
  it 
  can 
  

   and 
  does 
  move 
  from 
  place 
  to 
  place 
  with 
  considerable 
  rapidity. 
  

   If 
  a 
  quantity 
  of 
  freshly 
  collected 
  Oeratophyllum 
  is 
  put 
  into 
  

   an 
  aqnarium 
  that 
  is 
  unequally 
  illuminated, 
  the 
  Hydra 
  present 
  

   will 
  wander 
  from 
  the 
  Oeratophyllum 
  to 
  the 
  better 
  lighted 
  

   wall 
  of 
  the 
  aquarium 
  often 
  within 
  twenty-four 
  hours. 
  As 
  

   Hydra 
  cannot 
  swim 
  this 
  involves 
  a 
  rather 
  circuitous 
  journey. 
  

   But 
  even 
  without 
  such 
  a 
  directive 
  stimulus 
  its 
  movements 
  are 
  

   considerable. 
  For 
  example, 
  a 
  green 
  Hydra 
  was 
  placed 
  in 
  a 
  

   glass 
  dish, 
  and 
  this 
  was 
  set 
  over 
  a 
  sheet 
  of 
  ruled 
  paper 
  on 
  the 
  

   laboratory 
  table. 
  The 
  lines 
  of 
  the 
  paper 
  were 
  so 
  numbered 
  

   that 
  the 
  position 
  of 
  the 
  Hydra 
  could, 
  at 
  any 
  time, 
  be 
  charted 
  

   on 
  a 
  second 
  piece 
  of 
  ruled 
  paper 
  similarly 
  numbered. 
  The 
  

   chart 
  of 
  the 
  journeys 
  of 
  this 
  Hydra 
  is 
  shown 
  in 
  Fig. 
  2. 
  Al- 
  

   though 
  the 
  illumination 
  was 
  not 
  entirely 
  equal 
  from 
  all 
  sides 
  

   yet 
  it 
  was 
  not 
  one-sided 
  enough 
  to 
  influence 
  the 
  movements. 
  

   At 
  all 
  events 
  the 
  record 
  shows 
  no 
  such 
  effect. 
  

  

  Now, 
  how 
  are 
  these 
  movements 
  brought 
  about 
  ? 
  The 
  

   method 
  can 
  easily 
  be 
  seen 
  by 
  placing 
  a 
  single 
  Hydra 
  in 
  a 
  

   small 
  dish 
  and 
  observing 
  it 
  under 
  a 
  dissecting 
  microscope. 
  

   The 
  body, 
  expanded 
  and 
  with 
  expanded 
  tentacles, 
  bends 
  over 
  

   to 
  one 
  side. 
  As 
  soon 
  as 
  the 
  tentacles 
  touch 
  the 
  bottom 
  they 
  

   attach 
  themselves 
  and 
  contract. 
  (Zykoff 
  [^98] 
  claims 
  that 
  this 
  

   attachment 
  of 
  the 
  tentacles 
  is 
  by 
  means 
  of 
  pseudopodia, 
  but 
  

   during 
  observations 
  covering 
  many 
  mouths 
  I 
  have 
  never 
  seen 
  

   the 
  formations 
  he 
  figures.) 
  Now 
  one 
  of 
  two 
  things 
  happens 
  : 
  

  

  (1) 
  The 
  foot 
  may 
  loosen 
  its 
  hold 
  on 
  the 
  bottom, 
  and 
  the 
  body 
  

   contract. 
  In 
  this 
  manner 
  the 
  animal 
  comes 
  to 
  stand 
  on 
  its 
  

   tentacles 
  with 
  the 
  foot 
  pointing 
  upward. 
  The 
  body 
  now 
  bends 
  

   over 
  again 
  until 
  the 
  foot 
  attaches 
  itself 
  close 
  to 
  the 
  attached 
  

   tentacles. 
  These 
  loosen 
  in 
  their 
  turn, 
  and 
  so 
  the 
  Hydra 
  is 
  

   again 
  in 
  its 
  normal 
  position. 
  The 
  successive 
  steps 
  of 
  the 
  

   movement 
  are 
  illustrated 
  in 
  Fig. 
  3. 
  Trembley 
  described 
  the 
  

   movement, 
  and 
  illustrated 
  it 
  (1. 
  c. 
  Memoire 
  1, 
  PI. 
  3, 
  figs. 
  1-9) 
  ; 
  

  

  (2) 
  In 
  the 
  other 
  case 
  the 
  foot 
  is 
  not 
  detached, 
  but 
  glides 
  

   along 
  the 
  bottom 
  until 
  it 
  stands 
  close 
  to 
  the 
  tentacles, 
  which 
  

  

  