﻿G04 
  GEORGE 
  WAGNER. 
  

  

  on 
  this 
  point 
  is 
  lacking, 
  Hydra 
  being 
  purely 
  radiate, 
  as 
  far 
  

   as 
  is 
  known. 
  

  

  On 
  the 
  whole 
  Hydra, 
  in 
  its 
  manner 
  of 
  reaction 
  toward 
  

   mechanical 
  stimuli^ 
  is 
  a 
  close 
  parallel 
  of 
  Stentor 
  and 
  Vorti- 
  

   cella. 
  Jennings 
  ('02), 
  in 
  his 
  paper 
  on 
  these 
  forms, 
  has 
  dis- 
  

   cussed, 
  at 
  some 
  length, 
  the 
  psychological 
  questions 
  involved. 
  

   This 
  discussion 
  applies 
  with 
  equal 
  force 
  to 
  the 
  reactions 
  of 
  

   Hydra. 
  

  

  Rheoteopism. 
  

  

  In 
  order 
  to 
  determine 
  whether 
  Hydra 
  reacted 
  in 
  any 
  definite 
  

   way 
  to 
  a 
  current 
  of 
  water 
  a 
  very 
  simple 
  apparatus 
  was 
  con- 
  

   structed 
  by 
  taking 
  a 
  glass 
  tube 
  eighteen 
  inches 
  long 
  and 
  

   about 
  one 
  and 
  a 
  half 
  inches 
  inside 
  diameter. 
  A 
  small 
  hole 
  

   was 
  made 
  into 
  one 
  side 
  near 
  the 
  middle 
  for 
  the 
  introduction 
  

   of 
  the 
  animals. 
  The 
  tube 
  was 
  placed 
  horizontally, 
  and 
  so 
  

   arranged 
  that 
  water 
  flowed 
  into 
  it 
  over 
  a 
  dam 
  made 
  of 
  a 
  

   bisected 
  cork^ 
  and 
  flowed 
  out 
  at 
  the 
  other 
  end 
  over 
  a 
  similar 
  

   obstruction. 
  After 
  a 
  number 
  of 
  Hydra 
  were 
  introduced 
  the 
  

   current 
  of 
  water 
  was 
  turned 
  on. 
  It 
  could 
  be 
  increased 
  or 
  

   diminished 
  by 
  regulation 
  of 
  the 
  amount 
  of 
  water 
  supplied, 
  

   and 
  especially 
  by 
  tilting 
  the 
  tube. 
  In 
  this 
  apparatus 
  I 
  had 
  

   Hydra 
  under 
  observation 
  for 
  a 
  number 
  of 
  days, 
  but 
  there 
  

   was 
  absolutely 
  no 
  sign 
  of 
  response 
  to 
  the 
  currreut. 
  The 
  

   current 
  was 
  certainly 
  much 
  stronger 
  than 
  that 
  to 
  Avhich 
  the 
  

   Hydra 
  is 
  ordinarily 
  exposed 
  in 
  nature. 
  Yet 
  there 
  was 
  no 
  

   travelling 
  either 
  up 
  or 
  down 
  stream, 
  nor 
  any 
  curvature 
  of 
  the 
  

   body 
  with 
  or 
  against 
  the 
  current. 
  There 
  is 
  thus 
  no 
  evidence 
  

   of 
  rheotropism 
  in 
  Hydra. 
  

  

  Righting 
  Reaction. 
  

  

  Hydra 
  usually 
  has 
  its 
  foot 
  attached 
  to 
  the 
  substratum, 
  

   while 
  body 
  and 
  tentacles, 
  moderately 
  extended, 
  project 
  out 
  

  

  