﻿MIND 
  OF 
  AN 
  INSECT 
  SNODGRASS 
  

  

  395 
  

  

  In 
  the 
  higher 
  vertebrates, 
  the 
  seat 
  of 
  the 
  mental 
  faculties 
  is 
  

   undoubtedly 
  in 
  the 
  cerebral 
  hemispheres 
  of 
  the 
  brain, 
  where, 
  beneath 
  

   the 
  cellular 
  cortex, 
  there 
  are 
  great 
  masses 
  of 
  association 
  fibers 
  min- 
  

   gled 
  with 
  innumerable 
  nerve 
  endings 
  from 
  the 
  sense 
  organs 
  and 
  with 
  

   the 
  roots 
  of 
  nerves 
  connecting 
  with 
  motor 
  neurons 
  going 
  to 
  all 
  parts 
  

   of 
  the 
  body. 
  Within 
  the 
  insect 
  brain 
  likewise 
  are 
  various 
  bodies 
  of 
  

   association 
  fibers, 
  which 
  undoubtedly 
  are 
  important 
  internuncial 
  or 
  

   correlating 
  centers 
  in 
  the 
  insect 
  nervous 
  system. 
  (Fig. 
  3.) 
  Some 
  

   of 
  these 
  bodies 
  vary 
  in 
  size 
  and 
  complexity 
  within 
  certain 
  groups 
  of 
  

   insects 
  corresponding 
  in 
  a 
  general 
  way 
  to 
  what 
  might 
  be 
  regarded 
  

   as 
  the 
  mental 
  index 
  of 
  each 
  species, 
  judged 
  from 
  its 
  known 
  behavior. 
  

   The 
  correspondence 
  is 
  not 
  close 
  enough 
  in 
  all 
  insects, 
  however, 
  to 
  

   make 
  it 
  certain 
  that 
  any 
  part 
  of 
  the 
  insect 
  brain 
  is 
  a 
  definite 
  " 
  psy- 
  

   chical 
  center." 
  Experiments 
  have 
  shown 
  that 
  the 
  initiating 
  impulse 
  

  

  Fig. 
  3. 
  — 
  Cross-sections 
  of 
  the 
  brain 
  of 
  a 
  roach, 
  showing 
  diagrammatically 
  the 
  sensory 
  

   centers 
  of 
  the 
  brain, 
  and 
  the 
  courses 
  of 
  the 
  principal 
  nerve 
  tracts. 
  (From 
  Bret- 
  

   schneider) 
  

  

  A, 
  A, 
  centers 
  of 
  the 
  optic 
  ganglia 
  ; 
  AntNv, 
  base 
  of 
  antennal 
  nerve 
  ; 
  B, 
  protocerebral 
  

   bridge 
  ; 
  C, 
  central 
  body 
  ; 
  CoeCon, 
  circumoesophageal 
  connective 
  ; 
  D, 
  D, 
  corpora 
  pe- 
  

   dunculata, 
  or 
  " 
  mushroom 
  bodies 
  " 
  ; 
  O, 
  an 
  ocellus, 
  or 
  simple 
  eye 
  ; 
  OpNv, 
  optic 
  nerve 
  

   to 
  compound 
  eye 
  

  

  for 
  the 
  instinctive 
  acts 
  of 
  insects 
  originates 
  in 
  the 
  brain, 
  and 
  all 
  

   behavior 
  that 
  depends 
  on 
  the 
  sense 
  organs 
  innervated 
  from 
  the 
  

   brain 
  necessarily 
  is 
  activated 
  from 
  the 
  brain 
  center; 
  but, 
  as 
  will 
  be 
  

   shown 
  later, 
  the 
  brain 
  may 
  otherwise 
  be 
  quite 
  unnecessary 
  for 
  the 
  

   proper 
  performance 
  of 
  reflexes 
  in 
  a 
  complicated 
  instinct, 
  if 
  the 
  latter 
  

   can 
  be 
  stimulated 
  by 
  artificial 
  means. 
  

  

  The 
  evolution 
  of 
  the 
  nervous 
  mechanism 
  within 
  the 
  invertebrates 
  

   and 
  the 
  vertebrates 
  shows 
  only 
  the 
  development 
  of 
  one 
  structural 
  

   principle, 
  that 
  of 
  the 
  synapse 
  — 
  evidence 
  that 
  there 
  has 
  been 
  also 
  an 
  

   evolution 
  of 
  only 
  one 
  functional 
  principle, 
  with 
  nowhere 
  the 
  addi- 
  

   tion 
  of 
  a 
  new 
  and 
  peculiarly 
  " 
  mental 
  " 
  element. 
  The 
  basic 
  mecha- 
  

   nism, 
  however, 
  has 
  been 
  capable 
  of 
  development 
  along 
  two 
  

   divergent 
  lines 
  : 
  One, 
  specializing 
  on 
  the 
  permanently 
  closed 
  type 
  of 
  

   structure, 
  has 
  developed 
  the 
  reflex 
  method 
  of 
  function, 
  which 
  has 
  

   produced 
  its 
  best 
  results 
  in 
  the 
  highly 
  specialized 
  instincts 
  of 
  insects 
  ; 
  

  

  