﻿OK 
  SOME 
  MOVEMEKTS 
  A'ND 
  L'EACTIONS 
  OF 
  HYDRA. 
  585 
  

  

  On 
  Some 
  Movements 
  and 
  Reactions 
  of 
  Hydra. 
  

  

  By 
  

   Oeorge 
  Wagner, 
  M.A., 
  

  

  Instructor 
  in 
  Zoology, 
  University 
  of 
  Wisconsin. 
  

  

  This 
  study 
  of 
  the 
  movements 
  and 
  reactions 
  of 
  Hydra 
  was 
  

   undertaken 
  at 
  the 
  suggestion 
  of 
  Professor 
  H. 
  S. 
  Jennings, 
  

   whose 
  own 
  researches 
  (^97 
  — 
  '02) 
  on 
  the 
  reactions 
  of 
  protozoans 
  

   have 
  added 
  new 
  interest 
  to 
  this 
  line 
  of 
  work. 
  

  

  Trembley 
  (1744) 
  described 
  the 
  normal 
  movements 
  of 
  Hydra 
  

   in 
  considerable 
  detail. 
  Further 
  observations 
  on 
  the 
  same 
  

   subject 
  were 
  made 
  by 
  Baker 
  (1743), 
  Rosel 
  von 
  Rosenhof 
  

   (1755j, 
  Marshall 
  ('82), 
  and 
  Zoja 
  ('90). 
  The 
  works 
  of 
  Baker 
  

   and 
  von 
  Rosenhof 
  have 
  not 
  been 
  accessible 
  to 
  me. 
  Wilson 
  

   ('91) 
  made 
  a 
  detailed 
  study 
  of 
  phototaxis 
  in 
  Hydra, 
  while 
  

   Pearl 
  ('01) 
  investigated 
  its 
  behaviour 
  toward 
  the 
  constant 
  

   electric 
  current. 
  

  

  Normal 
  Movements. 
  — 
  Trembley 
  (I. 
  c.) 
  made 
  a 
  thorough 
  

   study 
  of 
  the 
  movements 
  of 
  Hydra, 
  and 
  his 
  description 
  of 
  them 
  

   is 
  fairly 
  complete. 
  Hydra 
  is 
  usually 
  attached 
  by 
  its 
  foot 
  to 
  

   some 
  solid 
  substratum, 
  as 
  a 
  submerged 
  stem 
  or 
  branch, 
  or 
  a 
  

   floating 
  leaf, 
  less 
  frequently 
  to 
  the 
  surface 
  film. 
  When 
  not 
  

   so 
  attached 
  it 
  is 
  helpless, 
  for 
  it 
  has 
  not 
  the 
  power 
  of 
  swimming. 
  

   When 
  attached 
  the 
  body 
  is 
  usually 
  moderately 
  expanded, 
  

   seldom 
  extremely 
  so. 
  In 
  Hydra 
  viridis 
  the 
  tentacles, 
  also 
  

   moderately 
  expanded, 
  extend 
  obliquely 
  outward 
  and 
  forward, 
  

   forming 
  the 
  framework 
  of 
  a 
  sort 
  of 
  funnel 
  with 
  the 
  hypostome 
  

   at 
  the 
  bottom. 
  In 
  Hydra 
  fusca, 
  and 
  especially 
  Hydra 
  

  

  VOL. 
  48, 
  PART 
  4. 
  NEW 
  SERIES. 
  * 
  42 
  

  

  