﻿406 
  

  

  ANNUAL 
  REPORT 
  SMITHSONIAIST 
  INSTITUTION, 
  1927 
  

  

  REACTION 
  TO 
  SOUND 
  ( 
  PH0N0TR0PI8M 
  ) 
  

  

  The 
  subject 
  of 
  insect 
  hearing 
  has 
  not 
  been 
  a 
  particularly 
  attrac- 
  

   tive 
  one 
  to 
  experimenters, 
  because 
  insects 
  generallj^ 
  make 
  no 
  response 
  

   to 
  ordinary 
  sounds. 
  Yet 
  the 
  " 
  singing 
  " 
  of 
  certain 
  male 
  insects 
  would 
  

   seem 
  to 
  imply 
  a 
  sense 
  of 
  hearing 
  in 
  the 
  females 
  at 
  least 
  of 
  the 
  same 
  

   species, 
  and 
  sense 
  organs 
  commonly 
  regarded 
  as 
  auditory 
  are 
  found 
  

   specially 
  developed 
  in 
  the 
  groups 
  of 
  singing 
  insects. 
  Many 
  other 
  in- 
  

   sects, 
  hovrever, 
  make 
  various 
  kinds 
  of 
  sounds, 
  some 
  of 
  which 
  are 
  

   merely 
  incidental 
  to 
  the 
  rubbing 
  of 
  skeletal 
  parts 
  on 
  each 
  other, 
  

   but 
  others 
  are 
  produced 
  by 
  special 
  rasping 
  surfaces. 
  

  

  Most 
  insects 
  are 
  well 
  provided 
  with 
  special 
  sense 
  organs 
  of 
  the 
  

   type 
  known 
  as 
  " 
  chordotonal," 
  in 
  the 
  sense 
  cells 
  of 
  which 
  there 
  are 
  

  

  specially 
  developed 
  sense 
  rods, 
  

   or 
  scolopalse, 
  attached 
  by 
  their 
  

   outer 
  ends 
  to 
  the 
  surface 
  cuti- 
  

   cula. 
  These 
  organs 
  occur 
  at 
  

   various 
  places 
  in 
  the 
  body 
  and 
  

   in 
  the 
  appendages. 
  They 
  have 
  

   no 
  external 
  receptive 
  parts, 
  but 
  

   in 
  some 
  cases 
  an 
  area 
  of 
  the 
  

   body 
  wall 
  surrounding 
  the 
  point 
  

   of 
  attachment 
  is 
  reduced 
  to 
  a 
  

   thin 
  tympanumlike 
  membrane. 
  

   Tympanal 
  chordotonal 
  organs 
  

   occur 
  on 
  the 
  base 
  of 
  the 
  abdomen 
  

   in 
  grasshoppers, 
  cicadas, 
  and 
  

   certain 
  moths, 
  on 
  the 
  base 
  of 
  

   the 
  thorax 
  in 
  other 
  moths 
  (fig. 
  

   5, 
  Tn)^ 
  and 
  on 
  the 
  forelegs 
  in 
  

   the 
  katydids 
  and 
  crickets. 
  A 
  special 
  chordotonal 
  organ 
  known 
  as 
  the 
  

   organ 
  of 
  Johnston 
  is 
  found 
  in 
  the 
  second 
  antennal 
  segment 
  of 
  nearly 
  

   all 
  insects, 
  the 
  sense 
  cells 
  being 
  attached 
  to 
  the 
  articular 
  membrane 
  

   at 
  the 
  base 
  of 
  the 
  movable 
  part 
  beyond. 
  Chordotonal 
  organs 
  in 
  gen- 
  

   eral, 
  as 
  suggested 
  by 
  Eggers, 
  may 
  be 
  vibration 
  receptors, 
  those 
  

   within 
  the 
  body 
  registering 
  the 
  vibratory 
  motion 
  of 
  the 
  muscles 
  in 
  

   action, 
  those 
  in 
  the 
  antennae 
  taking 
  account 
  of 
  the 
  movements 
  of 
  

   this 
  organ. 
  It 
  follows, 
  then, 
  that 
  a 
  chordotonal 
  organ 
  attached 
  to 
  a 
  

   membrane 
  capable 
  of 
  vibrating 
  to 
  sound 
  waves 
  might 
  become 
  a 
  

   sound 
  receptor, 
  or 
  also, 
  that 
  a 
  highly 
  developed 
  organ 
  of 
  Johnston, 
  

   such 
  as 
  that 
  of 
  the 
  mosquitoes 
  and 
  gnats, 
  might 
  respond 
  to 
  sound 
  

   vibrations. 
  

  

  Though 
  insects 
  are 
  usually 
  unresponsive 
  to 
  sounds, 
  their 
  indiffer- 
  

   ence 
  to 
  noise 
  can 
  not 
  be 
  taken 
  as 
  evidence 
  of 
  deafness. 
  Several 
  

  

  Fig. 
  5. 
  — 
  ^A 
  noctuid 
  moth 
  with 
  the 
  left 
  wings 
  

   removed, 
  showing 
  the 
  tympanal 
  organ 
  (Tm) 
  

   on 
  the 
  base 
  of 
  the 
  thorax 
  

  

  