﻿[11] 
  DEVELOPMENT 
  OF 
  THE 
  CETACEA. 
  437 
  

  

  in 
  which 
  the 
  tip 
  of 
  the 
  tail 
  forms 
  a 
  perfectly 
  round, 
  sometimes 
  slightly 
  

   exserted 
  hemispherical 
  tip 
  beyond 
  the 
  hinder 
  end 
  of 
  the 
  growing 
  fluke 
  

   folds 
  before 
  the 
  latter 
  have 
  lost 
  their 
  rounded 
  or 
  lobate 
  form. 
  This 
  

   notch 
  between 
  the 
  flukes 
  I 
  regard 
  as 
  representing 
  in 
  the 
  hind 
  limb 
  both 
  

   the 
  posterior 
  axillary 
  notches 
  or 
  re-entering 
  angles 
  behind 
  the 
  bases 
  of 
  

   the 
  fore 
  limbs 
  in 
  Cetacea. 
  It 
  represents 
  the 
  interval 
  between 
  the 
  edges 
  

   of 
  the 
  displaced 
  and 
  degenerate 
  pedes, 
  and 
  not 
  the 
  perineum 
  which 
  has 
  

   been 
  left 
  far 
  in 
  advance 
  of 
  the 
  flukes, 
  owing 
  to 
  the 
  manner 
  in 
  which 
  the 
  

   pedal 
  rudiments 
  have 
  been 
  carried 
  backwards 
  in 
  the 
  course 
  of 
  the 
  

   progress 
  of 
  the 
  degeneration 
  of 
  the 
  proximal 
  parts 
  of 
  the 
  limbs 
  due 
  to 
  

   inclusion, 
  and 
  the 
  gradual 
  hypertrophy 
  of 
  other 
  parts. 
  The 
  tail 
  has 
  

   therefore 
  assumed 
  the 
  function 
  of 
  the 
  hind 
  limbs 
  in 
  the 
  cetaceans, 
  and 
  

   although 
  no 
  longer 
  available 
  as 
  an 
  organ 
  of 
  locomotion 
  on 
  land, 
  as 
  are 
  

   the 
  hind 
  limbs 
  of 
  iflnnipeds: 
  it 
  is 
  strange 
  that 
  the 
  forces 
  of 
  Nature, 
  which 
  

   have 
  obviously 
  been 
  tending 
  to 
  the 
  same 
  end 
  in 
  the 
  latter 
  as 
  in 
  the 
  

   former, 
  should 
  have 
  had 
  to 
  evolve, 
  according 
  to 
  the 
  old 
  view, 
  a 
  new 
  

   organ 
  when 
  through 
  natural 
  processes 
  of 
  degeneration 
  in 
  one 
  direction, 
  

   coupled 
  with 
  hypertrophy 
  in 
  another, 
  an 
  old 
  one 
  could 
  be 
  transformed 
  

   into 
  the 
  structure 
  demanded 
  by 
  new 
  conditions. 
  

  

  The 
  partial 
  loss 
  of 
  the 
  ungues 
  in 
  the 
  pes 
  of 
  pinnipeds 
  has 
  been 
  re- 
  

   placed 
  by 
  a 
  condition 
  in 
  which 
  they 
  are 
  completely 
  absent 
  in 
  the 
  flukes 
  

   of 
  the 
  cetaceans 
  and 
  sirenians, 
  the 
  hairless 
  pedal 
  integuments 
  extend- 
  

   ing 
  in 
  the 
  first 
  far 
  beyond 
  the 
  nails. 
  This 
  hairless 
  and 
  nailless 
  condi- 
  

   tion 
  of 
  the 
  cetaceans 
  is 
  doubtless 
  correlated 
  with 
  habit, 
  and 
  has 
  be- 
  

   gun 
  to 
  manifest 
  itself 
  on 
  the 
  limbs 
  of 
  pinnipeds, 
  in 
  fact 
  has 
  been 
  almost 
  

   completely 
  attained 
  by 
  the 
  nearly 
  nude 
  walrus, 
  the 
  simple 
  teeth 
  of 
  which 
  

   arc 
  also 
  not 
  to 
  be 
  left 
  out 
  of 
  account 
  iu 
  this 
  comparison. 
  

  

  (G) 
  Anatomical 
  and 
  embryological 
  data. 
  — 
  Huxley, 
  with 
  his 
  usual 
  sa- 
  

   gacity, 
  has 
  told 
  us 
  by 
  implication 
  in 
  language 
  of 
  inimitable 
  clearness, 
  

   in 
  speaking 
  of 
  the 
  structural 
  characters 
  of 
  the 
  Pinnipeds, 
  what 
  are 
  

   some 
  of 
  the 
  morphological 
  changes 
  suffered 
  by 
  these 
  animals 
  in 
  the 
  

   course 
  of 
  their 
  evolution. 
  Although 
  in 
  part 
  almost 
  a 
  restatement 
  of 
  

   what 
  has 
  been 
  already 
  said, 
  I 
  may 
  be 
  pardoned 
  for 
  quoting 
  the 
  observ- 
  

   ations 
  of 
  so 
  eminent 
  an 
  authority. 
  He 
  says, 
  * 
  " 
  The 
  Pinnipedia, 
  or 
  seals 
  

   and 
  walruses, 
  are 
  those 
  Garnivora 
  which 
  come 
  nearest 
  the 
  Cetacea. 
  The 
  

   tail 
  is 
  united 
  by 
  a 
  fold 
  of 
  skin 
  which 
  extends 
  beyond 
  its 
  middle, 
  with 
  

   the 
  integument 
  covering 
  the 
  hind 
  legs. 
  These 
  are, 
  in 
  most 
  species, 
  

   permanently 
  stretched 
  out 
  in 
  a 
  line 
  with 
  the 
  axis 
  of 
  the 
  trunk." 
  The 
  

   English 
  anatomist 
  was 
  obviously 
  impressed 
  by 
  the 
  inclusion 
  by 
  integu- 
  

   ment 
  of 
  the 
  femoral 
  and 
  crural 
  parts 
  of 
  the 
  hind 
  limbs^ 
  together 
  with 
  

   the 
  tail, 
  as 
  seen 
  in 
  Pinnipeds. 
  

  

  Huxley 
  then 
  proceeds 
  (I.e.): 
  " 
  The 
  toes 
  are 
  completely 
  united 
  by 
  strong 
  

   webs, 
  and 
  the 
  straight 
  nails 
  are 
  sometimes 
  reduced 
  in 
  number, 
  or 
  even 
  

   altogether 
  abortive. 
  The 
  inner 
  and 
  outer 
  digits 
  of 
  the 
  pes 
  are 
  very 
  

   large." 
  

  

  * 
  Anatomy 
  of 
  vertebrated 
  animals, 
  p. 
  359. 
  

  

  