﻿124 
  THE 
  ZOOLOGIST. 
  

  

  mediate 
  change 
  in 
  the 
  character 
  and 
  aspect 
  of 
  the 
  country. 
  No 
  

   sooner 
  is 
  the 
  range 
  passed 
  than 
  we 
  meet 
  with 
  the 
  Red-breasted 
  

   Cockatoo 
  (Cacatua 
  roseicapilla) 
  , 
  which 
  is 
  never 
  found 
  on 
  the 
  

   eastern 
  side."* 
  Darwin, 
  of 
  course, 
  noticed 
  and 
  recorded 
  the 
  

   same 
  facts. 
  He 
  writes: 
  — 
  "On 
  the 
  opposite 
  sides 
  of 
  lofty 
  and 
  

   continuous 
  mountain 
  ranges, 
  of 
  great 
  deserts, 
  and 
  even 
  of 
  large 
  

   rivers, 
  we 
  find 
  different 
  productions." 
  f 
  Students 
  of 
  mammalian 
  

   geographical 
  distribution 
  often 
  find 
  the 
  great 
  rivers 
  real 
  divisional 
  

   lines. 
  Quite 
  recently 
  W. 
  L. 
  Sclater, 
  in 
  separating 
  the 
  subregions 
  

   of 
  the 
  Ethiopian 
  region, 
  has 
  used 
  the 
  watersheds 
  of 
  the 
  Senegal, 
  

   Congo, 
  and 
  Tana 
  rivers 
  for 
  that 
  purpose.! 
  Even 
  the 
  distribution 
  

   of 
  the 
  Tsetse-fly 
  is 
  similarly 
  affected. 
  Anderson 
  states 
  that 
  

   " 
  cattle 
  may 
  be 
  seen 
  grazing 
  securely 
  on 
  one 
  side 
  of 
  a 
  river, 
  

   whilst 
  the 
  opposite 
  bank 
  swarms 
  with 
  the 
  Tsetse. 
  "$ 
  Livingstone 
  

   found 
  the 
  banks 
  of 
  the 
  Chobe 
  River 
  separating 
  the 
  areas 
  of 
  this 
  

   insect. 
  " 
  We 
  lived 
  two 
  months 
  in 
  their 
  habitat, 
  which 
  was 
  in 
  

   this 
  case 
  as 
  sharply 
  defined 
  as 
  in 
  many 
  others, 
  for 
  the 
  south 
  

   bank 
  of 
  the 
  Chobe 
  was 
  infested 
  by 
  them, 
  and 
  the 
  northern 
  bank, 
  

   where 
  our 
  cattle 
  was 
  placed, 
  only 
  fifty 
  yards 
  distant, 
  contained 
  

   not 
  a 
  single 
  specimen." 
  || 
  And 
  Austen, 
  who 
  has 
  recently 
  mono- 
  

   graphed 
  these 
  flies, 
  states 
  that, 
  although 
  the 
  Tsetse 
  no 
  doubt 
  

   occurs 
  throughout 
  Portuguese 
  West 
  Africa, 
  there 
  appears 
  to 
  be 
  

   no 
  record 
  whatever 
  of 
  its 
  having 
  been 
  met 
  with 
  south 
  of 
  the 
  

   Congo. 
  IT 
  

  

  It 
  is, 
  however, 
  again 
  necessary 
  to 
  reiterate 
  here, 
  and 
  that 
  

   most 
  strongly, 
  that 
  no 
  universal 
  law 
  of 
  the 
  kind 
  can 
  be 
  found, 
  nor 
  

   is 
  the 
  existence 
  of 
  such 
  a 
  constant 
  factor 
  in 
  animal 
  distribution 
  

   advocated,** 
  the 
  desire 
  of 
  the 
  writer 
  being 
  merely 
  to 
  show 
  that 
  

   there 
  are 
  facts 
  to 
  prove 
  such 
  a 
  connection 
  in 
  many 
  cases, 
  and 
  

  

  * 
  ' 
  Among 
  Cannibals,' 
  p. 
  34. 
  

  

  f 
  ' 
  Origin 
  of 
  Species,' 
  6th 
  edit. 
  p. 
  317. 
  

  

  J 
  ' 
  Geographical 
  Journal,' 
  vol. 
  vii. 
  p. 
  287 
  ; 
  and 
  in 
  collaboration 
  with 
  

   P. 
  L. 
  Sclater, 
  'Geography 
  of 
  Mammals,' 
  p. 
  100. 
  

  

  § 
  ' 
  Lake 
  Ngami,' 
  p. 
  4S8. 
  

  

  || 
  ' 
  Miss. 
  Trav. 
  and 
  Researches 
  in 
  S. 
  Africa,' 
  p. 
  81. 
  

  

  IT 
  ' 
  Monograph 
  of 
  the 
  Tsetse-Flies,' 
  pp. 
  29-30. 
  

  

  :;::;: 
  In 
  his 
  paper 
  on 
  " 
  Biologic 
  Regions 
  and 
  Tabulation 
  Areas," 
  Mr. 
  C. 
  B. 
  

   Clarke 
  states 
  that 
  a 
  great 
  river 
  will 
  not 
  do 
  for 
  use 
  as 
  a 
  permanent 
  boundary 
  

   line, 
  " 
  as 
  nearly 
  all 
  the 
  plants 
  that 
  grow 
  on 
  one 
  bank 
  may 
  usually 
  be 
  found 
  

   on 
  the 
  other 
  " 
  (' 
  Phil. 
  Trans.' 
  vol. 
  clxxxiii. 
  p. 
  376). 
  Readers 
  of 
  Buckle's 
  ' 
  Hist. 
  

   Civilization 
  ' 
  will 
  probably 
  remember 
  an 
  early 
  footnote 
  to 
  the 
  effect 
  that 
  

  

  