﻿122 
  THE 
  ZOOLOGIST. 
  

  

  most 
  land 
  animals 
  could, 
  and 
  did 
  on 
  necessity, 
  swim, 
  and 
  there- 
  

   fore 
  to 
  a 
  great 
  extent 
  overcome 
  these 
  obstacles. 
  Still 
  there 
  was 
  

   so 
  much 
  to 
  be 
  said 
  on 
  both 
  sides 
  of 
  the 
  question, 
  that 
  I 
  have 
  

   continued 
  gathering 
  evidence, 
  and 
  have 
  thought 
  it 
  well 
  to 
  pub- 
  

   lish 
  some 
  of 
  the 
  facts 
  thus 
  acquired, 
  in 
  the 
  hope 
  that 
  other 
  

   zoologists 
  may 
  also 
  bring 
  grist 
  to 
  the 
  mill. 
  A 
  biological 
  enquiry 
  

   which 
  is 
  still 
  unencumbered 
  with 
  a 
  theory 
  is 
  surely 
  a 
  very 
  un- 
  

   common 
  phase 
  of 
  modern 
  thought, 
  and 
  should 
  be 
  attractive 
  on 
  

   that 
  ground 
  alone. 
  It 
  is, 
  however, 
  suggestive 
  to 
  the 
  last 
  degree, 
  

   and 
  appertains 
  as 
  much 
  to 
  the 
  requirements 
  of 
  the 
  historical 
  

   method, 
  or 
  perhaps 
  more 
  so, 
  than 
  to 
  the 
  seductive 
  paths 
  of 
  

   speculation. 
  I 
  have 
  dealt 
  with 
  the 
  question 
  in 
  its 
  rather 
  con- 
  

   tradictory 
  phases, 
  in 
  this 
  instalment 
  recognizing 
  the 
  divergent 
  

   action 
  of 
  rivers 
  on 
  animal 
  distribution, 
  and 
  in 
  a 
  subsequent 
  paper 
  

   propose 
  to 
  record 
  some 
  distributional 
  action 
  of 
  rivers, 
  and 
  to 
  

   give 
  details 
  of 
  land 
  animals 
  that 
  can, 
  or 
  rather 
  have 
  been 
  

   observed 
  to 
  swim. 
  

  

  Although 
  rivers 
  in 
  the 
  course 
  of 
  time 
  have 
  often, 
  and 
  do 
  

   often, 
  shift 
  their 
  channels, 
  as 
  Lyell 
  demonstrated 
  of 
  the 
  Thames 
  

   and 
  Mersey, 
  sometimes 
  deserting 
  and 
  subsequently 
  resuming 
  

   their 
  former 
  beds, 
  as 
  shown, 
  for 
  instance, 
  by 
  the 
  courses 
  of 
  the 
  

   Ardeche,* 
  they 
  still, 
  in 
  most 
  cases, 
  possess 
  a 
  considerable 
  

   antiquity,! 
  and 
  have 
  proved 
  factors 
  in 
  the 
  determination 
  of 
  

  

  :;; 
  Mardigny, 
  cf. 
  Marsh, 
  ' 
  Man 
  and 
  Nature,' 
  p. 
  402. 
  

  

  f 
  According 
  to 
  Prof. 
  Geikie, 
  there 
  can 
  be 
  no 
  doubt 
  that 
  both 
  in 
  Europe 
  

   and 
  North 
  America 
  the 
  rivers 
  at 
  a 
  comparatively 
  recent 
  geological 
  period 
  

   had 
  a 
  much 
  greater 
  volume 
  than 
  they 
  now 
  possess 
  ('Text-Book 
  Geology,' 
  

   2nd 
  edit. 
  p. 
  370). 
  In 
  North 
  America 
  the 
  duration 
  of 
  the 
  Niagara 
  has 
  been 
  

   computed 
  as 
  equalling 
  32,000 
  years 
  (J. 
  W. 
  Spencer, 
  'Am. 
  Journ. 
  Sci.,' 
  

   December, 
  1894). 
  These 
  changes 
  cannot 
  always 
  be 
  ascribed 
  to 
  a 
  great 
  

   antiquity. 
  Dr. 
  Gregory, 
  in 
  discussing 
  the 
  former 
  sources 
  of 
  the 
  Nile, 
  

   remarks 
  : 
  — 
  " 
  The 
  proof 
  which 
  I 
  hope 
  subsequently 
  to 
  publish 
  of 
  the 
  Pleisto- 
  

   cene 
  age 
  of 
  some 
  of 
  the 
  meridional 
  faults, 
  and 
  of 
  the 
  existence 
  of 
  a 
  former 
  

   outlet 
  from 
  Baringo 
  over 
  the 
  Lobat 
  Pass 
  to 
  the 
  north, 
  shows 
  that 
  the 
  river 
  

   system 
  must 
  have 
  been 
  very 
  differently 
  arranged 
  in 
  times 
  geologically 
  quite 
  

   recent" 
  (' 
  Geographical 
  Journal,' 
  vol. 
  iv. 
  p. 
  513). 
  Monsioa, 
  a 
  Bechuanaland 
  

   chief, 
  at 
  the 
  time 
  (1890) 
  more 
  than 
  eighty 
  years 
  of 
  age, 
  told 
  Mr. 
  Bryden 
  that 
  

   " 
  he 
  remembered 
  Sea-cows 
  (Hipioopotamus) 
  in 
  the 
  Molopo, 
  and 
  the 
  Molopo 
  

   of 
  to-day, 
  which, 
  like 
  other 
  South 
  African 
  rivers, 
  has 
  dwindled 
  greatly, 
  would 
  

   find 
  it 
  a 
  hard 
  matter 
  to 
  hold 
  a 
  single 
  Sea-cow 
  " 
  (' 
  Gun 
  and 
  Camera 
  in 
  South 
  

   Africa,' 
  p. 
  39). 
  Mr. 
  Bryden 
  further 
  remarks 
  : 
  — 
  "Anciently, 
  and 
  before 
  some 
  

  

  