﻿412 
  ANNUAL 
  EEPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  according 
  to 
  Kopec, 
  the 
  brain 
  furnishes, 
  besides 
  initiative 
  impulses, 
  

   a 
  tonus 
  to 
  the 
  entire 
  muscular 
  system, 
  for 
  all 
  the 
  muscles 
  become 
  lax 
  

   when 
  the 
  brain 
  is 
  removed. 
  Each 
  half 
  of 
  the 
  brain 
  affects 
  in 
  this 
  

   manner 
  only 
  the 
  muscles 
  of 
  its 
  own 
  side 
  of 
  the 
  body. 
  The 
  normal 
  

   silkworm 
  moths. 
  Miss 
  McCracken 
  says, 
  will 
  not 
  respond 
  to 
  artificial 
  

   stimuli 
  ; 
  Kopec 
  shows 
  that 
  the 
  inhibiting 
  centers 
  to 
  such 
  stimulation 
  

   lie 
  in 
  the 
  suboesophageal 
  ganglion. 
  Thus 
  the 
  normal 
  insect 
  is 
  com- 
  

   pelled 
  to 
  act 
  only 
  on 
  the 
  stimuli 
  received 
  from 
  the 
  brain. 
  

  

  When 
  it 
  is 
  said 
  that 
  the 
  brain 
  gives 
  the 
  initiative 
  impetus 
  to 
  a 
  

   series 
  of 
  instinct 
  reflexes 
  it 
  is 
  not 
  to 
  be 
  understood 
  that 
  the 
  stimulus 
  

   arises 
  spontaneously 
  within 
  the 
  brain. 
  The 
  brain 
  itself 
  must 
  receive 
  

   a 
  stimulus 
  from 
  some 
  other 
  source. 
  In 
  many 
  cases 
  the 
  primary 
  

   stimulus 
  for 
  an 
  action 
  initiated 
  through 
  the 
  brain 
  comes 
  probably 
  

   from 
  a 
  sense 
  organ 
  or 
  a 
  set 
  of 
  sense 
  organs, 
  the 
  brain 
  acting 
  merely 
  

   as 
  the 
  receiving 
  station 
  for 
  an 
  afferent 
  sensory 
  impulse, 
  which 
  is 
  dis- 
  

   tributed 
  from 
  it 
  to 
  the 
  ventral 
  ganglia 
  as 
  an 
  activating 
  force 
  that 
  

   sets 
  in 
  motion 
  the 
  nervous 
  apparatus 
  that 
  controls 
  the 
  final 
  reflex. 
  

   When 
  the 
  inhibitory 
  suboesophageal 
  ganglion 
  is 
  removed, 
  external 
  

   stimuli 
  not 
  dependent 
  on 
  the 
  brain 
  centers 
  may 
  directly 
  affect 
  the 
  

   reflex 
  centers 
  of 
  the 
  ventral 
  cord. 
  

  

  Primary 
  stimuli, 
  however, 
  can 
  not 
  always 
  be 
  assigned 
  to 
  an 
  ex- 
  

   ternal 
  sensory 
  cause; 
  an 
  important 
  class 
  of 
  behavior 
  phenomena 
  in 
  

   insects 
  must 
  be 
  attributed 
  to 
  internal 
  stimuli. 
  The 
  physical 
  nature 
  of 
  

   internal 
  stimuli 
  in 
  insects 
  is 
  not 
  known, 
  but 
  the 
  stimulating 
  effect 
  

   supposedly 
  comes 
  from 
  substances 
  produced 
  by 
  the 
  metabolism 
  of 
  the 
  

   organism, 
  comparable 
  to 
  the 
  hormones 
  which 
  correlate 
  physiological 
  

   processes 
  in 
  vertebrates. 
  Hormones 
  are 
  the 
  bod}'^ 
  messengers 
  by 
  

   which 
  one 
  organ 
  arouses 
  a 
  second 
  into 
  activity 
  when 
  the 
  time 
  is 
  ripe 
  

   for 
  combined 
  action, 
  or 
  for 
  two 
  organs 
  to 
  play 
  successive 
  roles 
  in 
  a 
  

   sequence 
  of 
  activities. 
  The 
  stimulus 
  that 
  impels 
  the 
  tent 
  caterpillars 
  

   to 
  leave 
  their 
  shelters 
  at 
  a 
  certain 
  time 
  each 
  day 
  and 
  go 
  out 
  on 
  the 
  

   branches 
  of 
  the 
  tree 
  to 
  feed 
  is 
  not, 
  most 
  probably, 
  a 
  sensation 
  of 
  

   hunger 
  but 
  a 
  physiological 
  activation 
  of 
  the 
  motor 
  mechanism, 
  

   effective 
  possibly 
  through 
  the 
  brain, 
  but 
  arising 
  internally 
  from 
  some 
  

   stimulus 
  engendered 
  by 
  the 
  lack 
  of 
  food 
  in 
  the 
  crop. 
  When 
  the 
  food 
  

   sac 
  is 
  filled, 
  another 
  impulse 
  sends 
  the 
  insects 
  back 
  into 
  the 
  tent, 
  in 
  

   the 
  protection 
  of 
  which 
  they 
  remain 
  during 
  the 
  period 
  of 
  digestion. 
  

   (See 
  Smithsonian 
  Report 
  for 
  1922, 
  p. 
  350.) 
  The 
  cocoon-spinning 
  

   instinct 
  of 
  a 
  caterpillar 
  becomes 
  active 
  at 
  a 
  certain 
  stage 
  of 
  the 
  

   insect's 
  life, 
  namely, 
  that 
  stage 
  just 
  preceding 
  the 
  series 
  of 
  metabolic 
  

   processes 
  which 
  will 
  transform 
  the 
  larva 
  into 
  a 
  moth, 
  and 
  there 
  can 
  

   be 
  little 
  doubt 
  that 
  substances 
  which 
  may 
  be 
  by-products 
  of 
  these 
  

   processes 
  act 
  directly 
  or 
  indirectly 
  as 
  the 
  stimulus 
  that 
  initiates 
  the 
  

   spinning 
  reflex. 
  The 
  special 
  method 
  and 
  technique 
  of 
  cocoon 
  build- 
  

   ing, 
  however, 
  are 
  inheritances 
  of 
  each 
  species, 
  and, 
  once 
  the 
  spinning 
  

  

  