﻿ORGANISM 
  AND 
  MECHANISM 
  123 
  

  

  compelling 
  constitutional 
  homesickness. 
  Professor 
  Yung 
  of 
  

   Geneva 
  took 
  twenty 
  bees 
  from 
  a 
  hive 
  near 
  the 
  lake, 
  put 
  them 
  

   into 
  a 
  box, 
  and 
  carried 
  them 
  six 
  kilometres 
  into 
  the 
  coun- 
  

   try, 
  where 
  he 
  set 
  them 
  free. 
  Seventeen 
  returned 
  to 
  the 
  hive. 
  

  

  V 
  * 
  f 
  

  

  some 
  of 
  them 
  in 
  an 
  hour. 
  

  

  The 
  fresh-water 
  mussel 
  carries 
  her 
  young 
  ones 
  in 
  her 
  outer 
  

   gill 
  plate, 
  and 
  keeps 
  them 
  there, 
  even 
  long 
  after 
  they 
  are 
  

   ready 
  to 
  emerge, 
  until 
  a 
  stickleback 
  or 
  a 
  minnow 
  comes 
  into 
  

   the 
  immediate 
  vicinity. 
  When 
  the 
  fish 
  comes 
  near, 
  the 
  

   mother-mussel, 
  whom 
  it 
  is 
  no 
  libel 
  to 
  call 
  i 
  acephalous 
  ', 
  

   liberates 
  a 
  crowd 
  of 
  the 
  pinhead-like 
  larva?, 
  which 
  swim 
  out 
  

   into 
  the 
  water, 
  snapping 
  their 
  tiny 
  toothed 
  valves, 
  and 
  

   secreting 
  viscid 
  attaching 
  threads. 
  They 
  have 
  the 
  begin- 
  

   nings 
  of 
  a 
  nervous 
  system; 
  they 
  are 
  sensitised 
  to 
  some 
  

   stimulus 
  from 
  the 
  fish 
  ; 
  thev 
  fasten 
  on 
  to 
  it 
  and 
  be;in 
  an- 
  

  

  v 
  O 
  

  

  other 
  chapter 
  of 
  their 
  life. 
  Even 
  in 
  the 
  laboratory, 
  when 
  

   thev 
  have 
  been 
  removed 
  from 
  the 
  mother, 
  thev 
  become 
  ex- 
  

  

  .' 
  I-' 
  

  

  traordiuarily 
  excited 
  if 
  a 
  morsel 
  of 
  minnow 
  be 
  dropped 
  into 
  

   the 
  dish 
  in 
  which 
  they 
  are. 
  They 
  respond 
  definitely 
  to 
  the 
  

   only 
  stimulus 
  which 
  will 
  enable 
  them 
  to 
  continue 
  their 
  life. 
  

   In 
  some 
  North 
  American 
  fresh-water 
  mussels 
  only 
  one 
  par- 
  

   ticular 
  kind 
  of 
  fish 
  will 
  serve 
  the 
  purpose 
  of 
  temporary 
  host. 
  

   In 
  the 
  remarkable 
  life-history 
  of 
  the 
  liver-fluke 
  of 
  the 
  

   sheep, 
  microscopic 
  ciliated 
  larvae 
  emerge 
  from 
  egg-cases 
  

   which 
  have 
  fallen 
  into 
  water. 
  These 
  larvae 
  have 
  no 
  organs 
  

   in 
  the 
  strict 
  sense, 
  no 
  hint 
  of 
  a 
  nervous 
  system, 
  and 
  only 
  a 
  

   few 
  cells 
  altogether. 
  They 
  have 
  energy 
  enough 
  to 
  go 
  on 
  

   swimming 
  for 
  about 
  a 
  day 
  in 
  the 
  water-pool. 
  They 
  may 
  

   come 
  in 
  contact 
  with 
  many 
  things, 
  sticks 
  and 
  straws, 
  roots 
  

   of 
  aquatic 
  plants 
  and 
  various 
  aquatic 
  animals, 
  but 
  there 
  is 
  

   (in 
  Britain) 
  only 
  one 
  touch 
  to 
  which 
  they 
  respond 
  that 
  

   of 
  the 
  small 
  fresh-water 
  snail, 
  Limncea 
  iruncaiula, 
  the 
  only 
  

  

  