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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  The 
  hiindfishes 
  are 
  also 
  very 
  unique 
  in 
  their 
  organization. 
  Two 
  

   of 
  the 
  known 
  species 
  have 
  well-developed 
  eyes, 
  and 
  live 
  in 
  lowland 
  

   streams 
  and 
  springs. 
  Such 
  are 
  doubtless 
  ancestors 
  of 
  the 
  eyeless 
  

   forms 
  of 
  the 
  cave 
  streams, 
  but 
  the 
  immediate 
  progenitors 
  and 
  rela- 
  

   tives 
  of 
  the 
  latter 
  seem 
  to 
  be 
  extinct. 
  They 
  were 
  fresh-water 
  forms, 
  

   and 
  of 
  the 
  same 
  general 
  stock 
  as 
  the 
  ancestors 
  of 
  the 
  killifishes, 
  mud- 
  

   minnows, 
  and 
  pike. 
  

  

  The 
  killifishes 
  and 
  the 
  allied 
  families 
  have 
  their 
  greatest 
  abundance 
  

   in 
  tropical 
  America, 
  which 
  is 
  probably 
  the 
  place 
  of 
  their 
  origin. 
  

   Some 
  of 
  them 
  are 
  especially 
  fishes 
  of 
  the 
  brackish 
  waters, 
  never 
  ven- 
  

   turing 
  far 
  out 
  to 
  sea. 
  Others 
  ascend 
  streams; 
  and 
  these 
  frequent 
  

   spring 
  waters, 
  and 
  waters 
  which 
  are 
  cold 
  and 
  clear. 
  Others, 
  non- 
  

   migratory, 
  occur 
  in 
  spring 
  waters 
  only. 
  

  

  The 
  three 
  species 
  of 
  mud 
  minnow 
  are 
  now 
  very 
  widely 
  separated 
  

   as 
  to 
  habitat, 
  although 
  very 
  similar 
  to 
  each 
  other 
  in 
  structure. 
  One 
  

   belongs 
  properly 
  to 
  our 
  Middle 
  West, 
  one 
  to 
  Atlantic 
  shore 
  drainage, 
  

   the 
  third 
  to 
  the 
  streams 
  of 
  Austria. 
  They 
  are 
  probably 
  remains 
  of 
  

   a 
  past 
  fauna, 
  in 
  which 
  the 
  group 
  was 
  more 
  fully 
  represented. 
  Our 
  

   mud 
  minnows 
  {Uinbra 
  ItTni 
  and 
  U. 
  'pygmcea) 
  are 
  am.ong 
  the 
  most 
  

   tenacious 
  of 
  life 
  of 
  all 
  fishes, 
  and 
  will 
  often 
  live 
  for 
  weeks 
  in 
  damp 
  

   muck 
  after 
  the 
  waters 
  of 
  a 
  pond 
  have 
  evaporated. 
  

  

  Of 
  the 
  six 
  or 
  eight 
  known 
  species 
  of 
  pike^ 
  one 
  is 
  cosmopolitan, 
  

   being 
  spread 
  over 
  northern 
  Asia 
  and 
  Europe 
  as 
  well 
  as 
  America, 
  

   while 
  the 
  other 
  species 
  are 
  somewhat 
  restricted 
  in 
  their 
  range. 
  The 
  

   common 
  pike 
  {Esox 
  lucius) 
  is 
  probably 
  the 
  parent 
  stock 
  of 
  all, 
  but 
  

   most 
  likely 
  originally 
  American. 
  The 
  affinities 
  of 
  the 
  mud 
  minnow 
  

   with 
  the 
  pike 
  are 
  not 
  remote, 
  and 
  doubtless 
  forms 
  between 
  the 
  two 
  

   have 
  existed. 
  

  

  The 
  hlackflsh 
  {Dallia 
  pectoralis) 
  of 
  Alaska 
  is 
  another 
  relative 
  of 
  

   the 
  mud 
  minnow 
  and 
  pike. 
  The 
  single 
  known 
  species 
  is 
  found 
  in 
  

   Alaska 
  and 
  eastern 
  Siberia 
  and 
  resists 
  cold 
  — 
  even 
  freezing 
  — 
  ^better 
  

   than 
  any 
  other 
  species. 
  It, 
  too, 
  is 
  probably 
  an 
  isolated 
  relic 
  of 
  a 
  

   disappearing 
  group. 
  

  

  The 
  common 
  eel 
  {Anguilla 
  species) 
  is 
  more 
  or 
  less 
  regularly 
  

   catadromous, 
  spawning 
  in 
  remote 
  seas. 
  Our 
  single 
  species 
  is 
  doubt- 
  

   less 
  of 
  marine 
  origin. 
  The 
  same 
  genus 
  is 
  widely 
  diffused 
  in 
  eastern 
  

   America, 
  in 
  Europe, 
  and 
  Asia, 
  though 
  curiously 
  wanting 
  on 
  our 
  

   Pacific 
  coasts 
  as 
  well 
  as 
  in 
  South 
  America. 
  

  

  The 
  sticklehacks 
  and 
  the 
  silversides 
  are 
  seashore 
  fishes, 
  the 
  former 
  

   of 
  cold, 
  the 
  latter 
  of 
  warm 
  regions. 
  Some 
  species 
  of 
  each 
  are 
  now 
  

   permanent 
  residents 
  of 
  fresh 
  water. 
  The 
  sticklebacks 
  especially 
  

   show 
  all 
  degrees 
  of 
  transition, 
  the 
  strictly 
  fluviatile 
  forms 
  being 
  as 
  

   usual 
  smaller 
  in 
  size 
  and 
  weaker 
  in 
  armature 
  than 
  the 
  marine 
  ones, 
  

   even 
  when 
  belonging 
  to 
  the 
  same 
  species. 
  

  

  