﻿RIVEBS 
  AS 
  FACTORS 
  IN 
  ANIMAL 
  DISTRIBUTION. 
  127 
  

  

  admits 
  the 
  divisional 
  effect 
  of 
  this 
  river 
  on 
  the 
  fauna 
  of 
  the 
  

   country 
  when 
  he 
  defines 
  the 
  West 
  African 
  subregion 
  as 
  extend- 
  

   ing 
  " 
  as 
  far 
  south 
  as 
  the 
  Congo."* 
  

  

  Confining 
  our 
  attention 
  to 
  the 
  same 
  continent, 
  we 
  may 
  find 
  

   examples 
  from 
  other 
  rivers. 
  The 
  main 
  stream 
  of 
  the 
  Mackenzie 
  

   River 
  — 
  a 
  considerable 
  tributary 
  of 
  the 
  Tana, 
  and 
  so 
  named 
  by 
  

   Chanler 
  and 
  Von 
  Hohnel— 
  may, 
  according 
  to 
  Neumann, 
  be 
  taken 
  

   as 
  the 
  line 
  of 
  demarcation 
  limiting 
  the 
  ranges 
  of 
  both 
  Coke's 
  

   Hartebeeste 
  and 
  Grevy's 
  Zebra.t 
  Selous, 
  writing 
  in 
  1881 
  on 
  the 
  

   Giraffe, 
  states 
  that 
  till 
  within 
  the 
  last 
  few 
  years 
  it 
  was 
  never 
  

   found 
  eastward 
  of 
  the 
  Eiver 
  Gwelo 
  (a 
  tributary 
  of 
  the 
  Zambesi 
  

   north 
  of 
  Matabeleland), 
  though 
  it 
  was 
  always 
  very 
  plentiful 
  in 
  

   the 
  sand-belts 
  to 
  the 
  westward 
  of 
  that 
  river. 
  This 
  fact 
  is 
  the 
  

   more 
  curious, 
  since 
  the 
  soil, 
  vegetation, 
  and 
  general 
  appearance 
  

   of 
  the 
  country 
  are 
  precisely 
  similar 
  on 
  both 
  sides 
  of 
  the 
  river, 
  

   which 
  during 
  a 
  great 
  portion 
  of 
  the 
  year 
  is 
  only 
  a 
  succession 
  of 
  

   pools, 
  and 
  therefore 
  does 
  not 
  offer 
  the 
  slightest 
  obstacle 
  to 
  any 
  

   animal 
  desirous 
  of 
  crossing 
  it. 
  During 
  the 
  last 
  three 
  or 
  four 
  

   years 
  a 
  few 
  Giraffes 
  have 
  extended 
  their 
  range 
  further 
  east- 
  

   wards 
  We 
  may 
  perhaps 
  here 
  hazard 
  the 
  supposition 
  that 
  in 
  

   more 
  ancient 
  times 
  this 
  waterway 
  was 
  of 
  a 
  deeper 
  and 
  more 
  

   extensive 
  description, 
  and 
  that 
  the 
  experience 
  of 
  a 
  restricted 
  

   range 
  once 
  caused 
  by 
  a 
  physical 
  barrier, 
  became 
  by 
  hereditary 
  

   transmission 
  a 
  conservative 
  "instinct" 
  in 
  the 
  minds 
  of 
  these 
  

   animals, 
  who 
  thus 
  seldom 
  or 
  never 
  attempted 
  to 
  ford 
  what 
  was 
  

   at 
  one 
  time 
  a 
  dangerous 
  or 
  impassable 
  current. 
  How 
  often 
  in 
  

   the 
  mental 
  evolution 
  of 
  ourselves 
  the 
  memory 
  of 
  a 
  dead 
  legend 
  

   keeps 
  us 
  from 
  the 
  easy 
  path 
  of 
  truth. 
  It 
  may 
  also 
  be 
  that 
  the 
  

   presence 
  of 
  Crocodiles 
  or 
  Alligators 
  may 
  often 
  prove 
  efficacious 
  

   in 
  preventing 
  animals 
  extending 
  their 
  range 
  beyond 
  a 
  river. 
  

   Bryden, 
  when 
  hunting 
  on 
  the 
  banks 
  of 
  the 
  Botletli, 
  in 
  South 
  

   Africa, 
  found 
  that 
  the 
  Lechwe 
  (Cobus 
  leche), 
  when 
  pursued, 
  

  

  * 
  ' 
  Text-Book 
  of 
  Zoogeography,' 
  p. 
  101. 
  

  

  f 
  ' 
  Elephant 
  Hunting 
  in 
  East 
  Equatorial 
  Africa,' 
  p. 
  27. 
  

  

  \ 
  Quoted 
  by 
  Lydekker, 
  ' 
  Roy. 
  Nat. 
  Hist.' 
  vol. 
  ii. 
  p. 
  333. 
  — 
  According 
  to 
  

   Sandeman, 
  " 
  a 
  Giraffe 
  is 
  the 
  most 
  defenceless 
  animal 
  imaginable, 
  and 
  has 
  

   nothing 
  to 
  show 
  fight 
  with 
  even 
  if 
  so 
  inclined 
  ; 
  it 
  is 
  easily 
  tired 
  out 
  and 
  run 
  

   down, 
  so, 
  although 
  fleet 
  for 
  a 
  short 
  distance, 
  it 
  does 
  not 
  afford 
  much 
  sport 
  " 
  

   (' 
  Eight 
  Months 
  in 
  an 
  Ox 
  Waggon,' 
  p. 
  324). 
  

  

  