﻿MIND 
  OF 
  AN 
  INSECT 
  — 
  SNODGRASS 
  399 
  

  

  common 
  origin 
  of 
  all 
  forms 
  of 
  animal 
  life 
  almost 
  demands 
  as 
  a 
  

   corollary 
  a 
  belief 
  in 
  the 
  universal 
  presence 
  or 
  potentiality 
  of 
  con^ 
  

   sciousness. 
  However, 
  in 
  dealing 
  with 
  the 
  results 
  of 
  experimental 
  

   work, 
  we 
  must 
  take 
  an 
  attitude 
  free 
  from 
  all 
  bias 
  of 
  theory, 
  lest 
  our 
  

   conclusions, 
  or 
  even 
  our 
  observations, 
  be 
  warped 
  in 
  the 
  making. 
  

  

  Though 
  the 
  true 
  nature 
  of 
  the 
  insect 
  mind 
  can 
  not 
  be 
  known 
  to 
  us, 
  

   there 
  is 
  still 
  ample 
  reason 
  for 
  studying 
  the 
  reactions 
  of 
  insects 
  to 
  

   sensory 
  stimuli; 
  the 
  information 
  so 
  obtained 
  will 
  give 
  the 
  closest 
  

   approach 
  to 
  an 
  understanding 
  of 
  the 
  relation 
  between 
  insect 
  be- 
  

   havior 
  and 
  the 
  environment, 
  a 
  thing 
  much 
  to 
  be 
  desired 
  for 
  many 
  

   practical 
  reasons. 
  The 
  economic 
  entomologist 
  finds 
  his 
  efforts 
  at 
  the 
  

   control 
  of 
  injurious 
  species 
  thwarted 
  on 
  all 
  sides 
  by 
  the 
  resources 
  of 
  

   the 
  insects, 
  resources 
  which 
  arise 
  from 
  mysterious 
  powers 
  with 
  which 
  

   the 
  insects 
  seem 
  to 
  be 
  endowed. 
  It 
  is 
  only 
  by 
  discovering 
  the 
  secrets 
  

   of 
  the 
  insects 
  that 
  the 
  practical 
  entomologist 
  will 
  be 
  able 
  to 
  put 
  him- 
  

   self 
  on 
  an 
  equal 
  footing 
  with 
  his 
  adversaries. 
  

  

  REACTION 
  TO 
  GRAVITT 
  (GEOTROPISM) 
  

  

  Insects 
  are 
  highly 
  responsive 
  to 
  gravity; 
  they 
  immediately 
  right 
  

   themselves 
  when 
  placed 
  on 
  their 
  backs, 
  which 
  act, 
  of 
  course, 
  might 
  

   be 
  attributed 
  to 
  a 
  mere 
  response 
  to 
  reversed 
  contact, 
  but 
  the 
  fact 
  

   that 
  insects 
  maintain 
  their 
  position 
  in 
  the 
  air 
  during 
  flight 
  shows 
  

   that 
  they 
  must 
  have 
  a 
  well-developed 
  sense 
  of 
  equilibrium. 
  Besides 
  

   this, 
  insects 
  know 
  up 
  from 
  down 
  in 
  space, 
  and 
  many 
  species 
  are 
  

   definitely 
  geotropic, 
  that 
  is, 
  on 
  upright 
  or 
  inclined 
  surfaces 
  they 
  go 
  

   invariably 
  upward 
  or 
  downward. 
  The 
  response 
  has 
  usually 
  some 
  

   relation 
  to 
  the 
  normal 
  feeding 
  or 
  other 
  habits 
  of 
  the 
  species. 
  Young 
  

   leaf-eating 
  caterpillars, 
  if 
  hatched 
  on 
  the 
  trunk 
  of 
  a 
  tree, 
  do 
  not 
  

   perish 
  for 
  lack 
  of 
  food; 
  being 
  negatively 
  geotropic, 
  their 
  first 
  con- 
  

   tinuous 
  movements 
  take 
  them 
  upward 
  to 
  the 
  branches 
  and 
  outward 
  

   to 
  the 
  foliage. 
  Mature 
  nymphs 
  of 
  the 
  cicada, 
  on 
  reaching 
  the 
  surface 
  

   of 
  the 
  earth 
  after 
  a 
  long 
  sojourn 
  beneath 
  its 
  surface, 
  are 
  likewise 
  

   negatively 
  geotropic. 
  They 
  crawl 
  skyward 
  on 
  the 
  first 
  upright 
  sur- 
  

   face 
  they 
  encounter. 
  Positive 
  geotropism 
  is 
  exhibited 
  by 
  many 
  tree- 
  

   inhabiting 
  caterpillars 
  just 
  before 
  the 
  time 
  of 
  the 
  pupal 
  transforma- 
  

   tion, 
  and 
  the 
  urge 
  to 
  go 
  downward 
  takes 
  them 
  to 
  the 
  earth, 
  within 
  

   which 
  some 
  species 
  bury 
  themselves 
  to 
  undergo 
  their 
  metamorphoses. 
  

  

  Considering 
  the 
  many 
  ways 
  by 
  which 
  insects 
  react 
  to 
  gravity, 
  and 
  

   especially 
  their 
  sense 
  of 
  balance 
  while 
  on 
  the 
  wing, 
  it 
  is 
  curious 
  that 
  

   no 
  organs 
  have 
  been 
  discovered 
  in 
  them, 
  except 
  in 
  a 
  few 
  doubtful 
  

   cases, 
  to 
  which 
  a 
  sense 
  of 
  equilibrium 
  can 
  be 
  referred. 
  Vertebrate 
  

   animals 
  have 
  a 
  well-developed 
  organ 
  of 
  equilibrium 
  in 
  the 
  semicir- 
  

   cular 
  canals 
  and 
  other 
  structures 
  of 
  the 
  inner 
  ear, 
  by 
  which 
  they 
  are 
  

  

  