﻿AIR-SACS 
  OF 
  THE 
  LOCUST. 
  181 
  

  

  treme 
  ramifications 
  only 
  retaining 
  their 
  original 
  setiform 
  structure 
  and 
  distribution. 
  

   In 
  the 
  truly 
  apterous 
  insects 
  the 
  tracheae 
  are 
  invariably 
  arborescent, 
  and 
  diminish 
  in 
  

   size 
  from 
  their 
  origiu 
  to 
  their 
  extremest 
  point 
  in 
  their 
  perfect 
  as 
  in 
  their 
  larva 
  condi- 
  

   tion, 
  and 
  they 
  are 
  invariably 
  smaller 
  in 
  diameter 
  and 
  have 
  fewer 
  ramifications 
  in 
  

   the 
  most 
  inactive 
  species. 
  

  

  In 
  the 
  flying 
  locusts 
  the 
  air-sacs 
  or 
  vesicles 
  are 
  not 
  less 
  numerous 
  

   than 
  in 
  the 
  bee, 
  and 
  we 
  think 
  that 
  in 
  proportion 
  to 
  the 
  body 
  they 
  are 
  

   more 
  numerous, 
  while 
  it 
  is 
  obvious 
  that 
  there 
  is 
  a 
  greater 
  number 
  of 
  

   large 
  sacs. 
  When 
  we 
  add 
  to 
  these 
  the 
  large 
  number 
  of 
  broad, 
  expanded, 
  

   or 
  dilated 
  air-tubes, 
  some 
  of 
  which 
  would 
  easily 
  be 
  confounded 
  with 
  the 
  

   sacs 
  themselves, 
  we 
  can 
  appreciate 
  the 
  wonderful 
  powers 
  of 
  the 
  Kocky 
  

   Mountain 
  locust 
  as 
  an 
  aeronaut. 
  With 
  a 
  greater 
  expanse 
  of 
  wing 
  than 
  

   in 
  any 
  of 
  its 
  congeners, 
  and 
  as 
  complex 
  an 
  arrangement 
  of 
  air-tubes 
  and 
  

   sacs, 
  it 
  is 
  able 
  to 
  rise 
  from 
  the 
  grouud 
  in 
  the 
  morning 
  and, 
  if 
  the 
  day 
  

   proves 
  clear, 
  remain 
  floating 
  in 
  the 
  air 
  for 
  hours, 
  until 
  near 
  sunset, 
  

   borne 
  hither 
  and 
  thither 
  by 
  gentle 
  baffling 
  breezes, 
  or 
  wafted 
  straight 
  on 
  

   in 
  its 
  course 
  eastward 
  from 
  its 
  mountain 
  home 
  for 
  miles 
  over 
  the 
  plains, 
  

   should 
  the 
  breeze 
  be 
  strong 
  and 
  steady. 
  Meanwhile 
  scarcely 
  as 
  much 
  

   muscular 
  force 
  is 
  spent 
  through 
  the 
  day 
  as 
  is 
  exerted 
  during 
  a 
  few 
  

   vigorous 
  hops 
  when 
  it 
  alights 
  on 
  the 
  ground. 
  • 
  

  

  In 
  the 
  possession 
  and 
  use 
  during 
  flight 
  of 
  these 
  air-sacs, 
  locusts 
  and 
  

   other 
  insects 
  may, 
  as 
  Newport 
  suggests, 
  be 
  compared 
  with 
  birds. 
  

  

  In 
  birds 
  the 
  respiratory 
  organs 
  are 
  not 
  only 
  vesicular 
  but 
  are 
  more 
  extensively 
  dis- 
  

   tributed 
  over 
  the 
  whole 
  body 
  than 
  in 
  any 
  other 
  vertobrata. 
  These, 
  as 
  every 
  anato- 
  

   mist 
  knows, 
  are 
  not 
  confined 
  merely 
  to 
  the 
  great 
  cavities 
  of 
  the 
  body, 
  but 
  are 
  extended 
  

   to 
  every 
  part 
  of 
  the 
  skeleton, 
  as 
  in 
  insects. 
  They 
  communicate 
  directly 
  with 
  the 
  

   interior 
  of 
  the 
  bones 
  of 
  the 
  wings 
  and 
  legs, 
  as 
  the 
  tracheae 
  of 
  the 
  thorax 
  are 
  extended 
  

   also 
  into 
  these 
  parts 
  in 
  insects. 
  This 
  distribution 
  in 
  both 
  is 
  more 
  extensive 
  and 
  com- 
  

   plete 
  in 
  the 
  most 
  active 
  species. 
  In 
  birds 
  which 
  are 
  unaccustomed 
  to 
  flight, 
  as 
  in 
  the 
  

   ostrich, 
  as 
  remarked 
  by 
  Mr. 
  Owen, 
  2 
  - 
  the 
  communication 
  of 
  the 
  respiratory 
  organs 
  with 
  

   the 
  bones 
  is 
  imperfect 
  ; 
  while 
  in 
  insects, 
  although 
  tracheae 
  exist 
  in 
  all, 
  the 
  vesicles 
  

   are 
  found 
  only 
  in 
  those 
  of 
  flight. 
  This 
  fact 
  extends 
  even 
  to 
  the 
  sexes 
  of 
  the 
  same 
  

   species. 
  Thus 
  vesicles 
  exist 
  in 
  the 
  males 
  of 
  the 
  common 
  glow-worm, 
  which 
  is 
  winged, 
  

   and 
  designed 
  to 
  search 
  out 
  the 
  apterous 
  female, 
  in 
  which 
  the 
  respiratory 
  organs 
  are 
  

   simply 
  tracheal. 
  The 
  like 
  conditions 
  exist 
  in 
  the 
  common 
  winter-moth, 
  Geometra 
  

   irunaria. 
  In 
  the 
  male 
  of 
  this 
  insect 
  I 
  have 
  found 
  the 
  vesicles 
  large 
  and 
  numerous, 
  

   but 
  not 
  a 
  trace 
  of 
  these 
  occurs 
  in 
  the 
  female. 
  The 
  trachea? 
  in 
  this 
  sex, 
  which 
  has 
  only 
  

   the 
  rudiments 
  of 
  wings, 
  are 
  larger 
  relatively 
  than 
  in 
  the 
  female 
  glow-worm, 
  and 
  are 
  

   precisely 
  in 
  that 
  condition 
  in 
  which 
  I 
  have 
  found 
  them 
  in 
  the 
  diurnal 
  Lepidoptera 
  

   •hortly 
  before 
  changing 
  to 
  the 
  pupa. 
  These 
  anatomical 
  facts 
  are 
  inferential 
  of 
  the 
  

   real 
  use 
  of 
  the 
  vesicles, 
  and 
  are 
  supported 
  by 
  an 
  observation 
  which 
  I 
  have 
  been 
  able 
  

   to 
  make 
  on 
  the 
  common 
  dung-beetle, 
  G-eotnqyes 
  stercorarius, 
  at 
  the 
  moment 
  when 
  it 
  is 
  

   preparing 
  to 
  take 
  flight. 
  A 
  specimen 
  of 
  this 
  insect 
  which 
  had 
  been 
  in 
  confinement 
  

   for 
  about 
  twenty-four 
  hours, 
  and 
  consequently 
  had 
  not 
  expanded 
  its 
  wings 
  during 
  

   that 
  time, 
  when 
  placed 
  on 
  a 
  table 
  immediately 
  prepared 
  to 
  escape. 
  After 
  walking 
  

   away 
  quickly 
  for 
  a 
  short 
  distance 
  it 
  began 
  to 
  respire 
  freely, 
  alternately 
  shortening 
  

   and 
  elongating 
  its 
  abdominal 
  segments 
  at 
  the 
  rate 
  of 
  about 
  forty 
  respirations 
  per 
  

   minute. 
  It 
  then 
  ceased 
  for 
  an 
  instant 
  and 
  slightly 
  separated 
  its 
  elytra 
  without 
  

   elevating 
  them, 
  and 
  began 
  again 
  to 
  respire 
  more 
  rapidly. 
  At 
  first 
  its 
  respiration 
  was 
  

  

  'Cyclopaedia 
  of 
  Anatomy 
  and 
  Physiology, 
  Art. 
  Aves., 
  vol. 
  i, 
  p. 
  341. 
  

  

  