﻿104 
  EEPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  larly 
  ; 
  this 
  is 
  especially 
  found 
  in 
  the 
  district 
  lying 
  between 
  the 
  Libyan 
  Desert 
  and 
  

   Iran, 
  between 
  the 
  Arabian 
  and 
  Persian 
  Gulfs 
  ; 
  in 
  Arabistan, 
  shut 
  in 
  by 
  its 
  adjacent 
  

   States, 
  and, 
  in 
  a 
  broader 
  sense, 
  with 
  the 
  regions 
  of 
  the 
  Jordan 
  and 
  Euphrates 
  south- 
  

   ward 
  toward 
  Jemen. 
  

  

  As- 
  a 
  further 
  evidence 
  that 
  all 
  these 
  conditions 
  are 
  necessary 
  to 
  their 
  

   excessive 
  increase 
  and 
  the 
  development 
  of 
  the 
  migratory 
  instinct, 
  it 
  is 
  

   found 
  that 
  P. 
  migratorius 
  is 
  unable 
  to 
  maintain 
  continued 
  existence 
  in 
  

   Germany 
  or 
  Poland 
  ; 
  and 
  that 
  G. 
  spretus 
  cannot 
  remain 
  permanent 
  on 
  

   the 
  prairies 
  of 
  Texas, 
  Kansas, 
  or 
  Nebraska, 
  or, 
  in 
  fact, 
  in 
  any 
  portion 
  

   of 
  the 
  area 
  we 
  have 
  denominated 
  the 
  " 
  temporary 
  region." 
  The 
  same 
  

   thing 
  is 
  also 
  doubtless 
  true 
  in 
  reference 
  to 
  the 
  other 
  migratory 
  species. 
  

  

  It 
  is 
  apparent, 
  therefore, 
  that 
  a 
  more 
  than 
  ordinarily 
  dry 
  and 
  rarefied 
  

   air 
  is 
  necessary 
  to 
  the 
  development 
  of 
  the 
  migratory 
  instinct 
  ; 
  at 
  least 
  

   we 
  are 
  justified 
  by 
  the 
  facts 
  in 
  assuming 
  this. 
  If 
  it 
  is 
  argued 
  that 
  this 
  

   condition 
  is 
  necessary 
  to 
  their 
  excessive 
  increase 
  in 
  numbers, 
  and 
  that 
  

   this 
  increase 
  makes 
  change 
  of 
  place 
  necessary 
  in 
  order 
  to 
  procure 
  food, 
  

   and 
  that 
  this 
  is 
  the 
  cause 
  of 
  migration, 
  we 
  reply 
  that 
  C. 
  spretus, 
  at 
  least, 
  

   is 
  essentially 
  migratory 
  in 
  its 
  native 
  habitat, 
  and 
  that 
  it 
  will 
  migrate 
  

   whether 
  in 
  excessive 
  numbers 
  or 
  not 
  ; 
  and 
  that 
  the 
  same 
  fact 
  appears 
  

   to 
  be 
  true 
  of 
  P. 
  migratorius. 
  It 
  follows, 
  then, 
  that 
  the 
  disposition 
  to 
  

   migrate 
  does 
  not 
  depend 
  upon 
  numbers, 
  but 
  is 
  owing 
  to 
  some 
  other 
  

   cause 
  5 
  for 
  why 
  should 
  C. 
  spretus 
  and 
  P. 
  migratorius 
  become 
  so 
  excess- 
  

   ively 
  multiplied 
  under 
  this 
  influence 
  and 
  other 
  species 
  under 
  the 
  same 
  

   conditions 
  not 
  ? 
  

  

  As 
  a 
  further 
  proof 
  that 
  want 
  of 
  food 
  is 
  not 
  only 
  not 
  the 
  remote 
  cause 
  

   of 
  migration, 
  but 
  is 
  not 
  always 
  the 
  immediate 
  cause, 
  we 
  may 
  adduce 
  the 
  

   now 
  well-known 
  fact 
  that 
  swarms 
  reared 
  in 
  the 
  temporary 
  regions 
  will 
  

   leave 
  the 
  fields 
  of 
  wheat 
  and 
  barley, 
  and 
  the 
  rich 
  grass 
  of 
  the 
  prairies, 
  

   to 
  return 
  to 
  the 
  barren 
  plains 
  from 
  which 
  their 
  ancestors 
  came. 
  It 
  is 
  

   also 
  a 
  fact 
  that 
  those 
  reared 
  in 
  the 
  mountain 
  canons, 
  where 
  there 
  is 
  

   abundant 
  food, 
  even 
  though 
  there 
  be 
  but 
  few 
  compared 
  with 
  the 
  supply 
  

   of 
  food, 
  will, 
  when 
  they 
  have 
  reached 
  the 
  proper 
  age, 
  fly 
  away 
  with 
  the 
  

   first 
  favorable 
  wind. 
  Nor 
  is 
  this 
  only 
  an 
  occasional 
  occurrence 
  but 
  a 
  

   constant 
  habit 
  ; 
  in 
  fact 
  it 
  is 
  almost 
  universally 
  the 
  case. 
  Both 
  on 
  the 
  

   plains 
  and 
  in 
  the 
  mountains, 
  even 
  when 
  there 
  is 
  abundant 
  food 
  at 
  hand, 
  

   often 
  when 
  the 
  day 
  is 
  warm 
  and 
  clear 
  and 
  no 
  wind 
  is 
  blowing, 
  they 
  may 
  

   be 
  seen 
  circling 
  upwards, 
  evidently 
  desiring, 
  as 
  shown 
  by 
  their 
  uneasy 
  

   movements, 
  to 
  move 
  away, 
  only 
  waiting 
  for 
  the 
  air 
  to 
  assist 
  them. 
  

  

  These 
  facts, 
  which 
  are 
  brought 
  out 
  more 
  fully 
  elsewhere, 
  I 
  thiuk 
  show 
  

   conclusively 
  that 
  the 
  desire 
  to 
  migrate 
  is 
  not 
  caused 
  by 
  want 
  of 
  food. 
  

   And 
  as 
  it 
  is 
  manifested 
  to 
  the 
  same 
  extent 
  in 
  their 
  native 
  habitats 
  as 
  in 
  

   the 
  temporary 
  regions, 
  when 
  parasites 
  are 
  absent 
  as 
  well 
  as 
  present, 
  it 
  

   cannot 
  depend 
  upon 
  the 
  presence 
  of 
  parasites. 
  

  

  As 
  we 
  have 
  heretofore 
  stated, 
  Bowles 
  assumes 
  that 
  the 
  males 
  are 
  

   largely 
  in 
  excess 
  of 
  the 
  females 
  ; 
  that 
  their 
  ardor 
  is 
  excessive, 
  while 
  the 
  

   females, 
  needing 
  a 
  larger 
  supply 
  of 
  food, 
  are 
  always 
  intent 
  on 
  feeding. 
  

   That 
  when 
  the 
  sun 
  has 
  dried 
  off 
  the 
  dew 
  in 
  the 
  morning, 
  the 
  females, 
  to 
  

  

  