﻿ANIMAL 
  BEHAVIOUR 
  179 
  

  

  using 
  psychological 
  terms. 
  We 
  inquire 
  into 
  the 
  creature's 
  

   power 
  of 
  profiting 
  by 
  experience, 
  as 
  to 
  its 
  pursuance 
  of 
  trial- 
  

   and-error 
  methods. 
  The 
  growth 
  of 
  experimental 
  psychology 
  

   has 
  furnished 
  many 
  a 
  welcome 
  check 
  to 
  interpretations, 
  show- 
  

   ing 
  some 
  to 
  be 
  too 
  simple 
  and 
  others 
  to 
  be 
  too 
  generous. 
  

   Some 
  weight 
  will 
  also 
  be 
  attached 
  to 
  the 
  degree 
  in 
  which 
  

   the 
  nervous 
  system 
  of 
  the 
  animal 
  in 
  question 
  resembles 
  ours, 
  

   or 
  that 
  of 
  some 
  types 
  previously 
  judged 
  to 
  be 
  capable 
  of, 
  

   let 
  us 
  say, 
  making 
  an 
  inference. 
  

  

  The 
  sound 
  practical 
  rule 
  is 
  to 
  try 
  to 
  re-describe 
  the 
  ob- 
  

   served 
  behaviour 
  in 
  as 
  simple 
  terms 
  as 
  possible 
  without 
  leav- 
  

   ing 
  out 
  any 
  essential 
  feature. 
  As 
  Prof. 
  Lloyd 
  Morgan 
  has 
  

   put 
  it, 
  " 
  In 
  no 
  case 
  may 
  we 
  interpret 
  an 
  action 
  as 
  the 
  out- 
  

   come 
  of 
  the 
  exercise 
  of 
  a 
  higher 
  psychical 
  faculty, 
  if 
  it 
  

   can 
  be 
  interpreted 
  as 
  the 
  outcome 
  of 
  the 
  exercise 
  of 
  one 
  

   which 
  stands 
  lower 
  in 
  the 
  psychological 
  scale 
  ' 
  (1894, 
  p. 
  53). 
  

   The 
  simplest 
  description 
  is 
  not 
  necessarily 
  the 
  true 
  one, 
  as 
  we 
  

   know 
  in 
  human 
  affairs 
  ; 
  but 
  the 
  scientific 
  method 
  is 
  to 
  hold 
  

   to 
  it 
  till 
  facts 
  force 
  us 
  to 
  give 
  it 
  up. 
  

  

  3. 
  Activities 
  of 
  Unicellular 
  Organisms. 
  

  

  Many 
  unicellular 
  organisms 
  show 
  restless 
  movements 
  

   which 
  may 
  be 
  ranked 
  at 
  the 
  foot 
  of 
  the 
  inclined 
  plane 
  of 
  

   behaviour. 
  As 
  long 
  as 
  certain 
  combustible 
  materials 
  within 
  

   the 
  organism 
  hold 
  out, 
  and 
  as 
  long 
  as 
  certain 
  external 
  stimuli 
  

   continue 
  to 
  act, 
  the 
  creatures 
  continue 
  moving; 
  and 
  we 
  see 
  

   them 
  responding 
  to 
  various 
  calls 
  which 
  summon 
  them 
  now 
  

   to 
  one 
  side 
  and 
  now 
  to 
  the 
  other. 
  This 
  is 
  like 
  the 
  unworked 
  

   ore 
  of 
  behaviour, 
  and 
  not 
  much 
  beyond 
  the 
  level 
  of 
  everyday 
  

   internal 
  activities. 
  We 
  may 
  speak 
  of 
  it 
  as 
  general 
  organismal 
  

   activity 
  among 
  unicellulars. 
  

  

  But 
  even 
  among 
  the 
  simplest 
  creatures 
  we 
  notice 
  three 
  

  

  