﻿ON 
  SOME 
  MOVEMENTS 
  AND 
  UEACTFONS 
  OF 
  HYDRA. 
  621 
  

  

  requires 
  a 
  combination 
  of 
  a 
  chemical 
  and 
  a 
  mechanical 
  

   stimulus 
  to 
  produce 
  a 
  food 
  reaction. 
  If 
  starvation 
  is 
  extreme 
  

   a 
  chemical 
  stimulus 
  alone 
  suffices. 
  

  

  12. 
  A 
  inechanical 
  stimulus 
  will 
  not 
  produce 
  a 
  discharge 
  of 
  

   nematocysts 
  ; 
  a 
  chemical 
  stimulus 
  will. 
  

  

  13. 
  The 
  action 
  of 
  the 
  chemical 
  is 
  probably 
  quite 
  direct, 
  not 
  

   involving 
  the 
  nervous 
  system. 
  Nematocyst 
  discharge 
  is 
  

   restricted 
  absolutely 
  to 
  the 
  area 
  touched 
  directly 
  by 
  the 
  

   chemical. 
  

  

  14. 
  The 
  nematocysts 
  can, 
  and 
  do, 
  pierce 
  the 
  epidermis 
  of 
  

   the 
  prey 
  at 
  which 
  they 
  are 
  discharged. 
  

  

  15. 
  Hydra 
  seems 
  to 
  be 
  able 
  to 
  paralyse 
  prey 
  without 
  dis- 
  

   charging 
  nematocysts. 
  

  

  Bibliography. 
  

  

  Baker, 
  H. 
  — 
  1743. 
  'Essays 
  on 
  tlie 
  Natural 
  History 
  of 
  the 
  Polypes,' 
  London, 
  

  

  17i3. 
  

   Baldwin, 
  J. 
  Mark. 
  — 
  '97. 
  'Mental 
  Development 
  in 
  the 
  Cliild 
  and 
  the 
  Race 
  : 
  

  

  Methods 
  and 
  Processes,' 
  New 
  York, 
  1897 
  (Second 
  Edition). 
  

   CiEsiELSKi, 
  T. 
  — 
  '7i. 
  'Beitra^'C 
  zur 
  Bioiogie 
  der 
  Pflanzen 
  (Cohn),' 
  Bd. 
  i, 
  

  

  zweites 
  Hel't., 
  p. 
  1. 
  

   Chun, 
  Cakl. 
  — 
  '93. 
  "Die 
  Canarischen 
  Siphonophoren. 
  II. 
  Monophyideu," 
  

  

  ' 
  Abliandl. 
  d. 
  Senkenh. 
  Nat. 
  Gesell.,' 
  1893. 
  

   Grenacher, 
  H. 
  — 
  '95. 
  'Zool. 
  Anzeiger,' 
  Bd. 
  viii, 
  1895, 
  p. 
  310. 
  

   Hartog, 
  M. 
  M.— 
  '80. 
  'Quart. 
  Journ. 
  Micr. 
  Sci.' 
  (N. 
  S.), 
  vol. 
  xx, 
  p. 
  248, 
  

  

  1880 
  A. 
  Same 
  volume 
  and 
  page. 
  

   Jennings, 
  H. 
  S. 
  — 
  '97. 
  'Journal 
  of 
  Physiology,' 
  vol. 
  xxi, 
  pp. 
  258 
  — 
  322. 
  

  

  1902. 
  'American 
  Journal 
  of 
  Physiology,' 
  vol. 
  viii, 
  pp. 
  23 
  — 
  GO. 
  [This 
  

  

  paper 
  contains 
  references 
  to 
  most 
  of 
  Jennings's 
  previous 
  papers.] 
  

   V. 
  Lendenfeld, 
  R. 
  — 
  '83. 
  'Zeitschr. 
  f. 
  wiss. 
  Zoologie,' 
  Bd. 
  xxxviii, 
  pp. 
  

  

  355—371. 
  

   Loeb, 
  J. 
  — 
  '91. 
  ' 
  Untersuchungen 
  zur 
  Pliysiologischen 
  Morphologic 
  der 
  

  

  Thiere,' 
  "I. 
  Ueber 
  Heteromorphose," 
  Wirzburg, 
  1891. 
  

  

  Makshall, 
  W.— 
  '82. 
  'Zeitschr. 
  f. 
  wiss. 
  Zoologie,' 
  BJ. 
  xxxvii, 
  pp. 
  664—702. 
  

  

  Peahl, 
  R. 
  — 
  '01 
  — 
  '03. 
  'Quart. 
  Journ. 
  Micr. 
  Sci.' 
  

  

  llosEL 
  V. 
  RosEXHor. 
  — 
  1755. 
  'Insektenbelustigungen,' 
  Theil 
  iii, 
  Niirnberg, 
  

   1755. 
  

  

  