﻿434 
  KEPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [8] 
  

  

  "The 
  steps 
  by 
  which 
  a 
  laud 
  mammal 
  may 
  have 
  been 
  modified 
  into 
  a 
  

   purely 
  aquatic 
  one 
  are 
  clearly 
  indicated 
  by 
  the 
  stages 
  which 
  still 
  

   survive 
  ainong 
  the 
  Garmvora, 
  in 
  the 
  Otarice 
  aud 
  in 
  the 
  true 
  seals. 
  A 
  

   further 
  change 
  in 
  the 
  same 
  direction 
  would 
  produce 
  an 
  auimal 
  some, 
  

   what 
  resembling 
  a 
  dolphin, 
  and 
  it 
  has 
  been 
  thought 
  that 
  this 
  may 
  have 
  

   been 
  the 
  route 
  by 
  which 
  the 
  cetacean 
  form 
  has 
  beeu 
  developed. 
  There 
  

   are, 
  however, 
  great 
  difficulties 
  in 
  the 
  way 
  of 
  tbis 
  view. 
  If 
  the 
  hind 
  

   limbs 
  had 
  ever 
  been 
  developed 
  into 
  the 
  very 
  efficient 
  aquatic 
  propelling 
  

   organs 
  they 
  present 
  in 
  the 
  seals, 
  it 
  is 
  not 
  easy 
  to 
  imagine 
  how 
  they 
  

   could 
  have 
  become 
  completely 
  atrophied 
  and 
  their 
  function 
  transferred 
  

   to 
  the 
  tail. 
  It 
  is 
  more 
  likely 
  that 
  the 
  Avhales 
  were 
  derived 
  from 
  animals 
  

   with 
  long 
  tails, 
  which 
  were 
  used 
  in 
  swimming, 
  eventually 
  with 
  such 
  

   effect 
  that 
  the 
  hind 
  limbs 
  became 
  no 
  longer 
  necessary. 
  The 
  powerful 
  

   tail, 
  with 
  its 
  lateral 
  cutaneous 
  flanges, 
  of 
  an 
  American 
  species 
  of 
  otter 
  

   (Ptcronura 
  SandbacMi) 
  may 
  give 
  an 
  idea 
  of 
  this 
  member 
  in 
  the 
  primi- 
  

   tive 
  Cetaceans." 
  * 
  

  

  Professor 
  Flower 
  has. 
  since 
  reiterated 
  the 
  preceding 
  views 
  with 
  more 
  

   emphasis, 
  as 
  follows: 
  

  

  " 
  One 
  of 
  the 
  methods 
  by 
  which 
  a 
  laud 
  mammal 
  may 
  have 
  been 
  changed 
  

   into 
  an 
  aquatic 
  one 
  is 
  clearly 
  shown 
  in 
  the 
  stages 
  which 
  still 
  survive 
  

   among 
  the 
  Carnivora. 
  The 
  seals 
  are 
  obviously 
  modifications 
  of 
  the 
  land 
  

   Carnivora, 
  the 
  Otarioe 
  or 
  sea 
  lions 
  and 
  sea 
  bears, 
  being 
  curiously 
  inter- 
  

   mediate. 
  Many 
  naturalists 
  have 
  been 
  tempted 
  to 
  think 
  that 
  the 
  whales 
  

   represent 
  a 
  still 
  further 
  stage 
  of 
  the 
  same 
  kind 
  of 
  modification. 
  So 
  

   firmly 
  has 
  this 
  idea 
  taken 
  root 
  that 
  in 
  most 
  popular 
  works 
  on 
  zoology, 
  

   in 
  which 
  an 
  attempt 
  is 
  made 
  to 
  trace 
  the 
  pedigree 
  of 
  existing 
  mammals, 
  

   the 
  Cetacea 
  are 
  definitely 
  placed 
  as 
  offshoots 
  of 
  the 
  Pinnipedia, 
  which 
  

   in 
  their 
  turn 
  are 
  derived 
  from 
  the 
  Carnivora. 
  But 
  there 
  is 
  to 
  my 
  mind 
  

   a 
  fatal 
  objection 
  to 
  this 
  view. 
  The 
  seal, 
  of 
  course, 
  has 
  much 
  in 
  common 
  

   with 
  the 
  whale, 
  inasmuch 
  as 
  it 
  is 
  a 
  mammal 
  adapted 
  for 
  an 
  aquatic 
  life, 
  

   but 
  it 
  has 
  been 
  converted 
  to 
  its 
  general 
  fish-like 
  form 
  by 
  the 
  peculiar 
  

   development 
  of 
  its 
  hind 
  limbs 
  into 
  instruments 
  of 
  propulsion 
  through 
  the 
  

   water; 
  for 
  though 
  the 
  thighs 
  and 
  legs 
  are 
  small, 
  the 
  feet 
  are 
  large, 
  aud 
  

   are 
  the 
  special 
  organs 
  of 
  locomotion 
  in 
  the 
  water, 
  the 
  tail 
  being 
  quite 
  

   rudimentary. 
  The 
  two 
  feet 
  applied 
  together 
  form 
  an 
  organ 
  very 
  like 
  

   the 
  tail 
  of 
  a 
  fish 
  or 
  whale, 
  and 
  functionally 
  representing 
  it, 
  but 
  only 
  

   functionally, 
  for 
  the 
  time 
  has, 
  I 
  trust, 
  quite 
  gone 
  by 
  when 
  the 
  Cetacea 
  

   were 
  defined 
  as 
  animals 
  with 
  the 
  l 
  hinder 
  limbs 
  united, 
  forming 
  a. 
  forked 
  

   horizontal 
  tail.' 
  .In 
  the 
  whales, 
  as 
  we 
  have 
  seen, 
  the 
  hind 
  limbs 
  are 
  

   aborted, 
  and 
  the 
  tail 
  developed 
  into 
  a 
  powerful 
  swimming 
  organ. 
  Now 
  

   it 
  is 
  difficult 
  to 
  suppose 
  that, 
  when 
  the 
  hind 
  limbs 
  had 
  once 
  become 
  so 
  

   well 
  adapted 
  to 
  a 
  function 
  so 
  essential 
  to 
  the 
  welfare 
  of 
  the 
  animal 
  as 
  

   that 
  of 
  swimming, 
  they 
  could 
  ever 
  have 
  become 
  reduced 
  and 
  their 
  action 
  

   transferred 
  to 
  the 
  tail. 
  The 
  animal 
  must 
  have 
  been 
  in 
  a 
  too 
  helpless 
  con- 
  

  

  *W. 
  H. 
  Flower, 
  Articlo 
  Mammalia, 
  Encycl. 
  Brittau., 
  9th 
  ed., 
  4to, 
  vol. 
  xv, 
  p. 
  394. 
  

   Edinburgh: 
  Black, 
  1883. 
  

  

  