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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  We 
  may 
  consider 
  the 
  fresh-water 
  fishes 
  alone 
  for 
  the 
  purpose 
  

   of 
  the 
  present 
  paper; 
  for 
  them 
  we 
  may 
  divide 
  the 
  land 
  areas 
  into 
  

   districts 
  and 
  zones 
  not 
  differino; 
  fundamentally 
  from 
  those 
  marked 
  

   out 
  for 
  mammals 
  and 
  birds. 
  The 
  river 
  basin, 
  bounded 
  by 
  its 
  shores 
  

   and 
  with 
  the 
  sea 
  at 
  its 
  mouth, 
  shows 
  many 
  resemblances, 
  from 
  

   the 
  point 
  of 
  view 
  of 
  fish 
  dispersion, 
  to 
  an 
  island 
  considered 
  as 
  the 
  

   home 
  of 
  a 
  mammal. 
  It 
  is 
  evident 
  that 
  with 
  fishes 
  the 
  differences 
  

   in 
  latitude 
  outweigh 
  those 
  of 
  continental 
  areas, 
  and 
  a 
  primary 
  

   division 
  into 
  Old 
  World 
  and 
  New 
  World 
  would 
  not 
  be 
  tenable. 
  

  

  The 
  chief 
  areas 
  of 
  distribution 
  of 
  fresh-water 
  fishes 
  we 
  may 
  

   indicate 
  as 
  follows: 
  

  

  With 
  Doctor 
  Giinther 
  ^ 
  we 
  may 
  recognize 
  first 
  the 
  northern 
  zone, 
  

   characterized 
  familiarly 
  by 
  the 
  presence 
  of 
  the 
  sturgeon, 
  salmon, 
  

   trout, 
  whitefish, 
  pike, 
  lamprey, 
  stickleback, 
  and 
  other 
  types 
  of 
  which 
  

   the 
  genera 
  and 
  occasionally 
  the 
  species 
  are 
  identical 
  in 
  Europe, 
  

   Siberia, 
  Canada, 
  Alaska, 
  and 
  most 
  of 
  the 
  northern 
  United 
  States, 
  

   Japan, 
  and 
  China. 
  This 
  is 
  subject 
  to 
  cross 
  division 
  into 
  two 
  great 
  

   districts 
  — 
  the 
  first 
  Europe-Asiatic, 
  the 
  second 
  North 
  American. 
  

   These 
  two 
  agree 
  very 
  closely 
  to 
  the 
  northward, 
  but 
  diverge 
  widely 
  

   to 
  the 
  southward, 
  developing 
  a 
  variety 
  of 
  specialized 
  genera 
  and 
  

   species, 
  and 
  both 
  of 
  them 
  passing 
  finally 
  by 
  degrees 
  into 
  the 
  

   equatorial 
  zone. 
  

  

  Still 
  another 
  line 
  of 
  division 
  is 
  made 
  by 
  the 
  Ural 
  Mountains 
  

   in 
  the 
  Old 
  World 
  and 
  by 
  the 
  Rocky 
  Mountains 
  in 
  the 
  New 
  World. 
  

   In 
  both 
  cases 
  the 
  eastern 
  region 
  is 
  much 
  richer 
  in 
  genera 
  and 
  species, 
  

   as 
  well 
  as 
  in 
  autochthonous 
  forms^ 
  than 
  the 
  western. 
  The 
  reason 
  

   for 
  this 
  lies 
  in 
  the 
  vastly 
  greater 
  extent 
  olE 
  the 
  river 
  basins 
  of 
  China 
  

   and 
  the 
  eastern 
  United 
  States 
  as 
  compared 
  with 
  those 
  of 
  western 
  

   Europe 
  or 
  of 
  the 
  California 
  region. 
  

  

  Minor 
  divisions 
  are 
  those 
  which 
  separate 
  the 
  Great 
  Lakes 
  region 
  

   from 
  the 
  streams 
  tributary 
  to 
  the 
  Gulf 
  of 
  Mexico; 
  and 
  in 
  Asia, 
  

   those 
  which 
  separate 
  China 
  from 
  tributaries 
  of 
  the 
  Caspian, 
  the 
  

   Black, 
  and 
  the 
  Mediterranean 
  Seas. 
  

  

  The 
  equatorial 
  zone 
  is 
  roughly 
  indicated 
  by 
  the 
  Tropics 
  of 
  Cancer 
  

   and 
  Capricorn. 
  Its 
  essential 
  feature 
  is 
  that 
  of 
  the 
  constantly 
  high 
  

   temperature, 
  and 
  the 
  peculiarities 
  of 
  its 
  divisions 
  are 
  caused 
  by 
  

   barriers 
  of 
  sea 
  or 
  mountains. 
  

  

  In 
  the 
  Tropics 
  the 
  best 
  line 
  of 
  separation 
  into 
  two 
  divisions 
  lies 
  

   in 
  the 
  presence 
  or 
  absence 
  of 
  the 
  great 
  family 
  of 
  dace 
  or 
  minnows 
  

   (Cyprinidse), 
  to 
  which 
  nearly 
  half 
  of 
  the 
  species 
  of 
  fresh-water 
  

   fishes 
  of 
  the 
  world 
  belong. 
  The 
  entire 
  group, 
  now 
  spread 
  every- 
  

   where 
  except 
  in 
  the 
  Arctic, 
  Antarctic, 
  South 
  America, 
  Australia, 
  and 
  

  

  2 
  " 
  Introduction 
  to 
  the 
  Study 
  of 
  Fishes." 
  

  

  