﻿ON 
  SOVIE 
  MOVEMENTS 
  AND 
  REACTIONS 
  OF 
  HYDKA. 
  605 
  

  

  into 
  the 
  water. 
  In 
  Hydi-a 
  viridis, 
  as 
  well 
  as 
  iu 
  the 
  other 
  

   forms, 
  the 
  tentacles 
  frequently 
  attach 
  themselves 
  to 
  the 
  sub- 
  

   stratum 
  and 
  assist 
  in 
  movement. 
  But 
  they 
  remain 
  so 
  attached 
  

   only 
  for 
  very 
  brief 
  periods. 
  The 
  foot, 
  on 
  the 
  other 
  hand, 
  is 
  

   seldom 
  detached. 
  Loeb 
  ('91) 
  has 
  shown 
  that 
  Cerianthus, 
  

  

  EiG. 
  4-. 
  — 
  B-ighting 
  reaction 
  of 
  Hydra 
  viridis. 
  A. 
  Hydra 
  placed 
  

   in 
  reversed 
  position, 
  tentacles 
  attached 
  to 
  substratum. 
  B. 
  Body 
  

   extending, 
  foot 
  end 
  bending 
  over. 
  C. 
  Foot 
  attached, 
  tentacles 
  

   ready 
  to 
  loosen. 
  D. 
  Upright 
  position 
  regained. 
  

  

  placed 
  in 
  an 
  nnnatural 
  position, 
  will 
  strive 
  successfully 
  even 
  

   under 
  difficulties 
  to 
  place 
  itself 
  in 
  such 
  a 
  position 
  that 
  its 
  

   long 
  axis 
  is 
  vertical, 
  with 
  head 
  up, 
  and 
  foot 
  attached 
  to 
  the 
  

   substratum. 
  In 
  Hydra 
  a 
  simple 
  experiment 
  shows 
  that 
  a 
  

   similar 
  righting 
  reaction 
  occurs. 
  A 
  green 
  Hydra, 
  strongly 
  

   contracted, 
  is 
  taken 
  and 
  placed 
  so 
  that 
  it 
  rests 
  on 
  the 
  bottom 
  

   of 
  a 
  watchglass 
  on 
  its 
  tentacles, 
  which 
  act 
  like 
  the 
  legs 
  of 
  a 
  

  

  