﻿182 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  slowly 
  but 
  gradually 
  increased, 
  until 
  a 
  few 
  seconds 
  before 
  it 
  attempted 
  to 
  expand 
  its 
  

   wings 
  and 
  to 
  elevate 
  itself 
  upon 
  them, 
  when 
  the 
  acts 
  of 
  respiration 
  became 
  exceedingly 
  

   rapid, 
  and 
  amounted 
  to 
  at 
  least 
  120 
  per 
  minute. 
  These 
  were 
  most 
  rapidly 
  performed, 
  

   and 
  were 
  then 
  suddenly 
  arrested 
  at 
  the 
  instant 
  before 
  it 
  attempted 
  to 
  unfold 
  the 
  

   wings. 
  During 
  this 
  increased 
  respiration 
  the 
  abdomen 
  of 
  the 
  insect 
  was 
  distinctly 
  

   enlarged, 
  and 
  it 
  was 
  quite 
  evident 
  that 
  this 
  enlargement 
  and 
  the 
  expansion 
  of 
  its 
  

   wings 
  were 
  being 
  effected 
  by 
  forced 
  inspirations, 
  and 
  maintained 
  by 
  the 
  expansion 
  

   of 
  the 
  air-sacs 
  over 
  the 
  whole 
  body, 
  and 
  the 
  communication 
  of 
  these 
  with 
  the 
  tracheal 
  

   vessels 
  in 
  the 
  wings 
  themselves, 
  As, 
  however, 
  the 
  wings 
  had 
  become 
  stiffened 
  and 
  

   dried 
  through 
  many 
  hours, 
  it 
  did 
  not 
  completely 
  succeed 
  in 
  its 
  attempts 
  to 
  escape, 
  

   but 
  only 
  partially 
  raised 
  itself 
  upon 
  them. 
  The 
  results 
  were 
  nevertheless 
  sufficiently 
  

   satisfactory 
  to 
  prove 
  to 
  me 
  that 
  the 
  respiratory 
  organs 
  became 
  distended 
  previous 
  to 
  

   the 
  act 
  of 
  flight, 
  as 
  the 
  entire 
  body 
  was 
  distinctly 
  enlarged 
  ; 
  the 
  effect 
  of 
  which 
  en- 
  

   largement, 
  together 
  with 
  an 
  increased 
  evolution 
  of 
  heat 
  in 
  the 
  body, 
  as 
  the 
  result 
  of 
  

   increased 
  respiration, 
  must, 
  of 
  consequence, 
  be 
  to 
  diminish 
  the 
  specific 
  gravity 
  of 
  the 
  

   insect, 
  and 
  thus, 
  by 
  lessening 
  the 
  degree 
  of 
  muscular 
  force 
  required 
  to 
  raise 
  it 
  on 
  its 
  

   wings, 
  considerably 
  augment 
  its 
  powers 
  of 
  locomotion, 
  which 
  seems 
  to 
  be 
  the 
  chief 
  

   use 
  for 
  which 
  the 
  vesicles 
  are 
  developed. 
  

  

  Origin 
  of 
  the 
  air-sacs. 
  — 
  When 
  we 
  carefully 
  examine 
  the 
  tracheaB 
  and 
  

   observe 
  that 
  in 
  the 
  locusts 
  many 
  are 
  dilated 
  and 
  so 
  expanded 
  that 
  at 
  

   first 
  one 
  is 
  inclined 
  to 
  regard 
  them 
  as 
  simply 
  long 
  vesicles, 
  and 
  then 
  

   observe 
  the 
  form 
  of 
  some 
  of 
  the 
  vesicles 
  and 
  their 
  relations 
  to 
  the 
  trache® 
  

   from 
  which 
  they 
  originate, 
  one 
  is 
  inclined 
  to 
  accept 
  the 
  following 
  theory 
  

   as 
  to 
  their 
  origin 
  given 
  by 
  the 
  distinguished 
  English 
  anatomist 
  whom 
  

   we 
  have 
  just 
  quoted. 
  

  

  The 
  respiratory 
  organs 
  are 
  always 
  simply 
  tracheal 
  in 
  the 
  larva 
  state 
  of 
  all 
  insects, 
  

   and 
  it 
  is 
  not 
  until 
  the 
  period 
  of 
  change 
  to 
  the 
  pupa 
  is 
  fast 
  approaching 
  that 
  they 
  begin 
  

   to 
  be 
  enlarged 
  even 
  in 
  those 
  in 
  which 
  vesicles 
  are 
  afterwards 
  the 
  most 
  numerous. 
  The 
  

   enlargement, 
  as 
  I 
  have 
  elsewhere 
  shown, 
  commences 
  in 
  Lepidopterous 
  insects 
  at 
  about 
  

   the 
  time 
  when 
  the 
  larva 
  ceases 
  to 
  feed. 
  It 
  is 
  perceptible 
  first 
  in 
  the 
  longitudinal 
  

   tracheae 
  of 
  the 
  thoracic 
  segments 
  of 
  the 
  Sphinx, 
  immediately 
  before 
  the 
  insect 
  enters 
  

   the 
  earth 
  ; 
  and 
  by 
  the 
  time 
  that 
  the 
  cell 
  in 
  which 
  it 
  is 
  to 
  undergo 
  its 
  transformation 
  

   is 
  completed, 
  the 
  tracheae 
  from 
  the 
  second 
  to 
  the 
  fifth 
  spiracles 
  are 
  distinctly 
  enlarged. 
  

   In 
  the 
  diurnal 
  species, 
  which 
  do 
  not 
  enter 
  the 
  earth 
  but 
  undergo 
  their 
  changes 
  in 
  the 
  

   open 
  air, 
  the 
  dilatation 
  of 
  the 
  tracheae 
  commences 
  while 
  the 
  insects 
  are 
  spinning 
  their 
  

   silken 
  threads. 
  When 
  this 
  labor 
  is 
  finished 
  and 
  they 
  have 
  remained 
  for 
  a 
  few 
  hours 
  

   at 
  rest, 
  the 
  skin 
  is 
  fissured 
  along 
  the 
  dorsal 
  surface 
  of 
  the 
  thoracic 
  segments 
  and 
  thrown 
  

   off, 
  the 
  change 
  to 
  the 
  pupa 
  is 
  effected, 
  and 
  the 
  longitudinal 
  tracheae 
  in 
  the 
  fifth 
  and 
  

   sixth 
  segments 
  are 
  dilated 
  into 
  vesicles, 
  which 
  continue 
  to 
  be 
  enlarged 
  during 
  the 
  first 
  

   few 
  days 
  after 
  the 
  change. 
  The 
  tracheae 
  of 
  the 
  third 
  and 
  fourth 
  segments 
  each 
  give 
  

   off 
  a 
  small 
  trunk 
  on 
  their 
  external 
  surface, 
  which 
  is 
  divided 
  into 
  two 
  branches, 
  and 
  is 
  

   involved 
  in 
  a 
  fold 
  of 
  the 
  new 
  tegument 
  that 
  is 
  formd 
  beneath 
  the 
  old 
  skin 
  of 
  the 
  larva 
  

   some 
  days 
  before 
  its 
  change. 
  The 
  fold 
  of 
  tegument 
  on 
  each 
  side 
  of 
  the 
  third 
  and 
  

   fourth 
  segments 
  is 
  supplied 
  with 
  ramifications 
  of 
  tracheae 
  from 
  these 
  minute 
  trunks, 
  

   and 
  very 
  closely 
  resembles 
  in 
  appearance 
  the 
  external 
  abdominal 
  branchiae 
  of 
  the 
  

   aquatic 
  larvae 
  of 
  Neuroptera. 
  It 
  is 
  these 
  folds 
  which 
  become 
  the 
  most 
  important 
  or- 
  

   gans 
  in 
  the 
  j)erfect 
  state 
  of 
  the 
  insect, 
  its 
  wings. 
  When 
  the 
  old 
  skin 
  of 
  the 
  larva 
  is 
  

   fissured 
  and 
  the 
  thoracic 
  segments 
  become 
  shortened, 
  as 
  the 
  skin 
  is 
  thrown 
  off, 
  pre- 
  

   vious 
  to 
  their 
  forming 
  one 
  region, 
  the 
  thorax, 
  the 
  tracheae 
  in 
  these 
  folds 
  are 
  rapidly 
  en- 
  

   larged 
  and 
  elongated, 
  and 
  mainly 
  assist 
  in 
  inducing 
  a 
  rush 
  of 
  blood 
  into 
  these 
  struct- 
  

   ures, 
  which 
  are 
  thus 
  expanded 
  on 
  the 
  sides 
  of 
  the 
  new 
  pupa 
  as 
  the 
  rudimentary 
  wings. 
  

   This 
  elongation 
  of 
  the 
  small 
  trunks 
  at 
  the 
  sides 
  of 
  the 
  longitudinal 
  tracheae 
  in 
  the 
  

   thorax 
  relieves 
  them 
  of 
  a 
  portion 
  of 
  that 
  tension 
  which 
  results 
  from 
  the 
  powerful 
  

  

  