﻿108 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  additional 
  impulse. 
  I 
  think 
  it 
  more 
  than 
  probable 
  that 
  the 
  effect 
  of 
  the 
  

   dry 
  and 
  rarefied 
  condition 
  of 
  the 
  air 
  upon 
  them 
  is 
  such 
  that 
  when 
  they 
  

   arrive 
  at 
  the 
  perfect 
  state 
  and 
  the 
  season 
  of 
  their 
  amours 
  arrives 
  the 
  

   migratory 
  impulse 
  is 
  increased 
  by 
  irritation 
  of 
  some 
  kind 
  which 
  causes 
  

   an 
  uneasy, 
  restless 
  feeling. 
  Although 
  I 
  do 
  not 
  believe 
  their 
  migrations 
  

   are 
  for 
  the 
  purpose 
  of 
  carrying 
  on 
  their 
  amours, 
  yet 
  I 
  think 
  it 
  highly 
  

   probable 
  that 
  at 
  this 
  stage 
  of 
  their 
  lives 
  the 
  migratory 
  impulse 
  is 
  strong- 
  

   est, 
  and 
  that 
  the 
  excited 
  condition 
  of 
  all 
  the 
  internal 
  organs 
  is 
  probably 
  

   one 
  cause 
  of 
  its 
  being 
  strongest 
  at 
  this 
  time. 
  But 
  that 
  the 
  migratory 
  

   impulse 
  does 
  not 
  depend 
  upon 
  the 
  perfected 
  condition 
  of 
  the 
  insects 
  is 
  

   shown 
  by 
  the 
  strong 
  disposition 
  of 
  the 
  young 
  to 
  migrate. 
  Hence, 
  the 
  

   <?ause 
  which 
  operates 
  to 
  produce 
  this 
  effect 
  acts 
  upon 
  the 
  larvae 
  and 
  

   pupae 
  as 
  well 
  as 
  the 
  perfect 
  insects. 
  

  

  There 
  are 
  some 
  things 
  connected 
  with 
  the 
  movements 
  of 
  the 
  locusts 
  

   which 
  appear 
  to 
  indicate 
  something 
  more 
  than 
  an 
  impulse 
  simply 
  to 
  fly, 
  

   ivhich 
  is 
  the 
  weak 
  point 
  of 
  the 
  theory 
  if 
  limited 
  to 
  irritating 
  or 
  uneasy 
  

   sensations 
  as 
  the 
  only 
  cause 
  of 
  migration 
  ; 
  one 
  is 
  the 
  evident 
  disposition 
  

   often 
  manifested 
  by 
  the 
  locusts 
  to 
  go 
  in 
  a 
  given 
  direction. 
  This 
  was 
  

   4shown 
  in 
  our 
  first 
  report 
  and 
  need 
  not 
  be 
  repeated 
  here. 
  

  

  That 
  hunger 
  will 
  cause 
  them 
  to 
  move 
  from 
  place 
  to 
  place 
  in 
  search 
  of 
  

   food 
  is 
  certainly 
  true, 
  but 
  it 
  would 
  be 
  a 
  violent 
  presumption 
  to 
  say 
  that 
  

   a 
  swarm 
  in 
  Montana 
  starts 
  from 
  there 
  on 
  a 
  voyage 
  to 
  Nebraska 
  in 
  

   search 
  of 
  food, 
  or 
  from 
  Southern 
  Eussia 
  to 
  Germany. 
  Having 
  the 
  mi- 
  

   gratory 
  instinct 
  already 
  implanted 
  in 
  them, 
  and 
  with 
  it 
  the 
  adaptation 
  

   to 
  long 
  flights, 
  when 
  once 
  they 
  start 
  in 
  search 
  of 
  food 
  it 
  is 
  not 
  incon- 
  

   sistent 
  with 
  reason 
  to 
  suppose 
  they 
  continue 
  on 
  their 
  course 
  as 
  driven 
  

   by 
  the 
  wind 
  until 
  they 
  find 
  food 
  or 
  are 
  exhausted. 
  So 
  far 
  we 
  can 
  con- 
  

   nect 
  cause 
  and 
  effect, 
  but 
  we 
  must 
  confess 
  that 
  there 
  are 
  still 
  facts 
  

   connected 
  with 
  their 
  movements 
  unexplained. 
  For 
  example, 
  as 
  will 
  here- 
  

   after 
  be 
  shown 
  in 
  the 
  chapter 
  on 
  meteorological 
  influences, 
  those 
  bred 
  in 
  

   the 
  temporary 
  regions 
  in 
  their 
  attempts 
  to 
  return 
  to 
  their 
  native 
  breed- 
  

   ing-grounds 
  are 
  not 
  governed 
  by 
  the 
  prevailing 
  course 
  of 
  the 
  winds, 
  for 
  

   if 
  this 
  were 
  so 
  some 
  would 
  go 
  in 
  one 
  direction 
  and 
  some 
  in 
  another 
  j 
  

   whereas 
  those 
  bred 
  in 
  Nebraska 
  and 
  southward 
  exhibit 
  a 
  uniform 
  dis- 
  

   position 
  to 
  go 
  northward 
  or 
  northwest 
  even 
  when 
  the 
  prevailing 
  course 
  

   of 
  the 
  wind 
  is 
  adverse. 
  

  

  