﻿130 
  THE 
  ZOOLOGIST. 
  

  

  species 
  from 
  those 
  found 
  in 
  the 
  sources 
  of 
  the 
  same 
  rivers. 
  The 
  

   nature 
  of 
  the 
  tropical 
  ocean 
  into 
  which 
  all 
  the 
  Himalayan 
  rivers 
  

   debouche 
  is 
  no 
  doubt 
  the 
  proximate 
  cause 
  of 
  the 
  absence 
  of 
  

   Salmonida." 
  * 
  

  

  As 
  with 
  " 
  Mimicry 
  " 
  and 
  " 
  Protective 
  Eesemblance," 
  the 
  

   solution 
  of 
  the 
  riddle 
  of 
  geographical 
  distribution 
  must 
  depend 
  

   largely 
  on 
  the 
  teachings 
  of 
  geology 
  and 
  palaeontology. 
  The 
  

   explanation 
  of 
  the 
  present 
  is 
  only 
  made 
  possible 
  by 
  the 
  story 
  of 
  

   the 
  past. 
  Embryology, 
  Anthropology 
  (including 
  Sociology) 
  — 
  

   nay, 
  even 
  most 
  biological 
  enquiries 
  — 
  are 
  better 
  understood 
  the 
  

   farther 
  we 
  go 
  back. 
  In 
  the 
  beginning 
  was 
  the 
  great 
  evolutionary 
  

   impulse. 
  Dr. 
  Gregory 
  has 
  well 
  remarked 
  : 
  " 
  The 
  anomalies 
  of 
  

   zoological 
  distribution, 
  especially 
  in 
  regard 
  to 
  the 
  fresh-water 
  

   faunas, 
  appear 
  still 
  more 
  difficult 
  of 
  explanation, 
  unless 
  con- 
  

   sidered 
  in 
  the 
  light 
  of 
  geological 
  changes." 
  t 
  Some 
  of 
  the 
  

   large 
  rivers 
  still 
  contain 
  living 
  links 
  with 
  the 
  Triassic 
  strata 
  of 
  

   Europe, 
  and 
  secondary 
  rocks 
  of 
  India 
  and 
  South 
  Africa, 
  in 
  the 
  

   existing 
  Lung-fishes 
  (Lepidosirenidce). 
  In 
  the 
  Burnett 
  and 
  Mary 
  

   rivers 
  of 
  Queensland, 
  the 
  Australian 
  Lung-fish 
  (Ceratodusforsteri) 
  

   is 
  generally 
  considered 
  a 
  distinct 
  generic 
  survival, 
  whilst 
  the 
  

   Mud-fish 
  of 
  the 
  Amazons 
  (Lcpidosiren 
  paradoxa), 
  and 
  its 
  African 
  

   relation 
  {Protopterus 
  annectans), 
  so 
  abundant 
  in 
  the 
  Gambia, 
  

   bear 
  witness 
  not 
  only 
  to 
  the 
  antiquity 
  of 
  the 
  animal 
  type, 
  but 
  

   also 
  to 
  the 
  age 
  of 
  the 
  streams 
  in 
  which 
  they 
  are 
  still 
  found. 
  

  

  The 
  rivers 
  of 
  the 
  American 
  continent 
  have 
  a 
  similar 
  character. 
  

   Mr. 
  Wallace 
  has 
  given 
  the 
  cases 
  of 
  certain 
  species 
  of 
  Saki 
  Monkey 
  

  

  :;: 
  ' 
  Himalaj^an 
  Journals,' 
  vol. 
  ii. 
  p. 
  187. 
  — 
  The 
  Salmon 
  is 
  unknown 
  in 
  any 
  

   of 
  the 
  rivers 
  flowing 
  into 
  the 
  Mediterranean 
  (' 
  Roy. 
  Nat. 
  Hist.' 
  vol. 
  v. 
  p. 
  495). 
  

   It 
  is 
  also 
  stated 
  that 
  in 
  South 
  Africa, 
  Crocodiles 
  " 
  are 
  only 
  found 
  in 
  the 
  rivers 
  

   which 
  run 
  to 
  the 
  eastward" 
  (J. 
  Garbett 
  Wood, 
  'Through 
  Matabeleland,' 
  

   p. 
  43). 
  The 
  temperature 
  of 
  rivers 
  also 
  may 
  vary 
  in 
  places 
  in 
  a 
  very 
  quali- 
  

   fying 
  manner 
  for 
  piscian 
  distribution. 
  E. 
  Andre 
  describes 
  a 
  stream 
  as 
  being 
  

   in 
  temperature 
  several 
  degrees 
  lower 
  than 
  that 
  of 
  the 
  Caura, 
  owing 
  to 
  its 
  

   being 
  completely 
  shaded 
  from 
  the 
  rays 
  of 
  the 
  sun 
  by 
  the 
  tall 
  trees 
  of 
  the 
  

   forest 
  through 
  which 
  it 
  flows 
  (' 
  A 
  Naturalist 
  in 
  the 
  Guianas,' 
  p. 
  137). 
  Of 
  

   course 
  waterfalls 
  are 
  always 
  obstacles. 
  " 
  In 
  the 
  Yosemite 
  Valley, 
  in 
  Cali- 
  

   fornia, 
  for 
  example, 
  the 
  Trout 
  ascend 
  the 
  Merced 
  river 
  to 
  the 
  base 
  of 
  a 
  

   vertical 
  fall. 
  They 
  cannot 
  rise 
  above 
  this, 
  and 
  so 
  the 
  streams 
  and 
  lakes 
  

   above 
  this 
  fall 
  are 
  destitute 
  of 
  fish 
  " 
  (Jordan 
  and 
  Kellogg, 
  ' 
  Animal 
  Life,' 
  

   p. 
  274). 
  

  

  f 
  'Geographical 
  Journal,' 
  vol. 
  iv. 
  p. 
  512, 
  

  

  