﻿56 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  more 
  remarkable 
  invasions 
  were 
  noted. 
  It 
  is 
  also 
  possible, 
  and 
  we 
  are 
  

   inclined 
  to 
  think 
  more 
  than 
  probable, 
  that, 
  in 
  most 
  of 
  the 
  countries 
  

   where 
  locust 
  visitations 
  have 
  long 
  been 
  observed, 
  their 
  invasions 
  have 
  

   become 
  more 
  frequent 
  than 
  formerly, 
  but 
  the 
  records 
  of 
  visitation 
  can 
  

   not 
  be 
  relied 
  upon 
  for 
  the 
  determination 
  of 
  this 
  question. 
  Be 
  this 
  as 
  it 
  

   may, 
  the 
  facts 
  we 
  have 
  presented 
  are 
  sufficient 
  to 
  show 
  conclusively 
  that 
  

   their 
  migrations 
  are 
  not 
  governed 
  by 
  any 
  regular 
  periodicity, 
  and 
  hence 
  

   depend 
  upon 
  some 
  influence 
  which 
  is 
  irregular 
  in 
  its 
  operations, 
  as, 
  for 
  

   example, 
  climatic 
  changes. 
  

  

  Yet, 
  notwithstanding 
  this 
  conclusion, 
  we 
  cannot 
  pass 
  on 
  without 
  call- 
  

   ing 
  attention 
  to 
  the 
  fact 
  that 
  if 
  we 
  take 
  the 
  years 
  of 
  the 
  great 
  general 
  in- 
  

   vasions 
  of 
  Central 
  Europe, 
  1333, 
  1650, 
  1693, 
  1748, 
  and 
  1825 
  ; 
  of 
  Spain, 
  1495, 
  

   1542, 
  1619, 
  and 
  1682 
  ; 
  of 
  Algiers 
  and 
  adjoining 
  regions, 
  1799,1845, 
  1866, 
  

   and 
  the 
  recent 
  one 
  of 
  1878 
  $ 
  and 
  the 
  noted 
  locust 
  years 
  in 
  our 
  own 
  west- 
  

   ern 
  country, 
  to 
  wit, 
  1820, 
  1855, 
  1866, 
  and 
  1874-76, 
  the 
  interim 
  in 
  each 
  

   case 
  is 
  very 
  nearly 
  a 
  multiple 
  of 
  11 
  years. 
  

  

  II. 
  — 
  PERMANENT 
  BREEDINGS 
  GROUNDS 
  OR 
  AREAS 
  OF 
  PERMANENT 
  

  

  DISTRIBUTION. 
  

  

  That 
  migratory 
  locusts 
  occasionally 
  extend 
  their 
  flights 
  into 
  sections 
  

   where 
  they 
  are 
  not 
  found 
  as 
  permanent 
  residents 
  is 
  too 
  well 
  known 
  to 
  

   require 
  proof, 
  and 
  that 
  they 
  sometimes 
  continue 
  in 
  these 
  extralimital 
  

   areas 
  for 
  two 
  or 
  three 
  years 
  by 
  reproduction 
  has 
  been 
  clearly 
  demon- 
  

   strated. 
  As 
  a 
  proof 
  of 
  this 
  assertion 
  we 
  have 
  only 
  to 
  refer 
  to 
  the 
  paper 
  

   by 
  Koppen 
  already 
  mentioned, 
  and 
  our 
  former 
  report. 
  Therefore, 
  in 
  at- 
  

   tempting 
  to 
  mark 
  the 
  boundaries 
  of 
  the 
  distribution 
  of 
  these 
  erratic 
  in- 
  

   sects, 
  it 
  has 
  been 
  found 
  necessary 
  to 
  draw 
  at 
  least 
  two 
  lines, 
  one 
  to 
  bound 
  

   the 
  inner 
  or 
  permanent 
  area 
  and 
  another 
  to 
  designate 
  the 
  limits 
  of 
  fluc- 
  

   tuation, 
  or, 
  to 
  quote 
  the 
  words 
  of 
  M. 
  Preudhomme 
  de 
  Borre 
  : 
  152 
  

  

  In 
  this 
  study, 
  so 
  interesting, 
  there 
  is 
  one 
  point 
  on 
  which 
  we 
  should 
  insist. 
  It 
  is 
  this 
  : 
  

   that 
  the 
  observations 
  of 
  M. 
  Koppen 
  tend 
  to 
  confirm 
  the 
  principle 
  of 
  zoological 
  geo- 
  

   graphy, 
  that 
  the 
  area 
  of 
  a 
  species 
  cannot 
  be 
  limited 
  on 
  the 
  map 
  by 
  a 
  simple 
  curve, 
  

   but 
  between 
  places 
  where 
  the 
  species 
  exist 
  in 
  a 
  constant 
  or 
  normal 
  manner 
  and 
  those 
  

   where 
  its 
  absence 
  is 
  constant 
  there 
  is 
  always 
  a 
  zone, 
  often 
  very 
  broad, 
  of 
  temporary 
  

   visitations, 
  which 
  is 
  to 
  the 
  area 
  properly 
  so 
  called 
  what 
  the 
  penumbra 
  is 
  to 
  the 
  light, 
  

   within 
  the 
  zone, 
  of 
  which 
  the 
  exterior 
  limit 
  is 
  much 
  more 
  easily 
  traced 
  than 
  the 
  inner; 
  

   this 
  last 
  is 
  subject 
  to 
  continual 
  oscillations 
  with 
  some 
  undulatory 
  movements 
  depend- 
  

   ent 
  on 
  the 
  centrifugal 
  or 
  expansive 
  tendency 
  of 
  the 
  species 
  and 
  from 
  the 
  resistance 
  

   which 
  opposes 
  it, 
  and 
  external 
  circumstances, 
  and 
  evidently 
  also 
  the 
  tendency 
  of 
  other 
  

   Bpecies 
  to 
  spread 
  out, 
  with 
  which 
  it 
  carries 
  on 
  a 
  struggle 
  for 
  existence. 
  

  

  Koppen, 
  in 
  order 
  to 
  express 
  fully 
  the 
  relation 
  of 
  P. 
  migratorius 
  to 
  the 
  

   regions 
  in 
  which 
  it 
  has 
  been 
  observed, 
  found 
  it 
  necessary 
  to 
  trace 
  upon 
  

   the 
  map 
  three 
  concentric 
  lines, 
  one 
  marking 
  the 
  limit 
  of 
  its 
  permanent 
  

   distribution, 
  corresponding 
  to 
  what 
  we 
  in 
  our 
  first 
  report 
  termed 
  " 
  per- 
  

   manent 
  breeding-grounds 
  " 
  ; 
  a 
  second, 
  outside 
  of 
  this, 
  marking 
  the 
  limits 
  

   of 
  its 
  temporary 
  existence 
  in 
  all 
  its 
  stages 
  of 
  development 
  j 
  and 
  a 
  third 
  or 
  

  

  162 
  See 
  former 
  >i^ 
  ort, 
  p. 
  475. 
  

  

  