﻿[9] 
  DEVELOPMENT 
  OF 
  THE 
  CETACEA. 
  435 
  

  

  dition 
  to 
  maintain 
  its 
  existence 
  during 
  tlie 
  transference 
  if 
  it 
  took 
  place, 
  

   as 
  we 
  must 
  suppose, 
  gradually. 
  It 
  is 
  far 
  more 
  reasonable 
  to 
  suppose 
  

   that 
  whales 
  were 
  derived 
  from 
  animals 
  with 
  large 
  tails, 
  which 
  were 
  used 
  

   in 
  swimming, 
  eventually, 
  with 
  such 
  effect 
  that 
  the 
  hind 
  limbs 
  became 
  

   no 
  longer 
  necessary, 
  and 
  so 
  gradually 
  disappeared. 
  The 
  powerful 
  tail, 
  

   with 
  lateral 
  cutaneous 
  flanges, 
  of 
  an 
  American 
  species 
  of 
  otter 
  (Ptero- 
  

   nura 
  Sandbachii), 
  or 
  the 
  still 
  more 
  familiar 
  tail 
  of 
  the 
  beaver, 
  may 
  give 
  

   some 
  idea 
  of 
  this 
  member 
  in 
  the 
  primitive 
  Cetacea. 
  I 
  think 
  that 
  this 
  

   consideration 
  disposes 
  of 
  the 
  principal 
  argument 
  that 
  the 
  whales 
  are 
  

   related 
  to 
  the 
  seals, 
  as 
  most 
  of 
  the 
  other 
  resemblances, 
  such 
  as 
  those 
  in 
  

   the 
  characters 
  of 
  their 
  teeth, 
  are 
  evidently 
  analogous 
  resemblances 
  re- 
  

   lated 
  to 
  similarity 
  of 
  habit.' 
  7 
  * 
  

  

  (5) 
  Another 
  view 
  of 
  the 
  phytogeny 
  of 
  cetaceans. 
  — 
  I 
  do 
  not 
  assert 
  that 
  

   the 
  hinder 
  limbs 
  are 
  united 
  to 
  form 
  a 
  forked 
  horizontal 
  tail 
  ; 
  what 
  I 
  do 
  

   assert 
  is 
  that, 
  in 
  consequence 
  of 
  the 
  rotation 
  and 
  extension 
  backwards 
  

   of 
  the 
  hind 
  limbs 
  of 
  a 
  type 
  in 
  which 
  the 
  hind 
  limbs 
  were 
  thus 
  thrown 
  

   back 
  parallel 
  with 
  the 
  tail 
  and 
  included 
  by 
  the 
  integument 
  of 
  the 
  body, 
  

   these 
  limbs 
  were 
  rendered 
  more 
  or 
  less 
  immobile, 
  as 
  a 
  result 
  of 
  which 
  

   the 
  limb 
  skeleton, 
  its 
  muscles 
  and 
  the 
  pelvis 
  have 
  atrophied, 
  leaving, 
  

   however, 
  the 
  integuments 
  of 
  the 
  feet 
  in 
  a 
  posterior 
  position 
  on 
  either 
  

   side 
  of 
  the 
  end 
  of 
  the 
  tail 
  as 
  the 
  rudiments 
  of 
  flukes. 
  This, 
  I 
  submit, 
  

   is 
  to 
  me 
  a 
  far 
  more 
  reasonable 
  hypothesis 
  than 
  any 
  which 
  derives 
  the 
  

   flukes 
  from 
  an 
  entirely 
  different 
  source, 
  viz, 
  the 
  cutaneous 
  flanges 
  of 
  

   the 
  tail 
  of 
  the 
  sea-otter. 
  

  

  The 
  argument 
  that 
  " 
  the 
  animal 
  must 
  have 
  been 
  in 
  a 
  too 
  helpless 
  con- 
  

   dition 
  to 
  maintain 
  its 
  existence 
  during 
  the 
  transference 
  if 
  it 
  took 
  place, 
  

   as 
  we 
  must 
  suppose, 
  gradually," 
  can 
  be 
  met 
  by 
  citing 
  the 
  seals 
  them- 
  

   selves, 
  animals 
  which 
  certainly 
  are 
  somewhat 
  helpless 
  on 
  laud, 
  yet 
  re- 
  

   markably 
  graceful 
  and 
  active 
  in 
  the 
  water. 
  The 
  Cetacea, 
  on 
  the 
  other 
  

   hand, 
  are 
  quite 
  helpless 
  on 
  land, 
  but 
  certainly 
  not 
  in 
  the 
  water, 
  the 
  

   medium 
  in 
  which 
  this 
  gradual 
  transference 
  of 
  function 
  must 
  have 
  oc- 
  

   curred 
  after 
  the 
  hind 
  limbs 
  became 
  more 
  and 
  more 
  useless 
  as 
  a 
  means 
  

   of 
  progression 
  on 
  land, 
  when 
  such 
  a 
  Protocetacean 
  form 
  would 
  not 
  

   again 
  venture 
  upon 
  the 
  latter. 
  It 
  is 
  thus 
  rendered 
  evident 
  that 
  

   Professor 
  Flower's 
  arguments 
  are 
  not 
  as 
  insuperable 
  as 
  they 
  at 
  flrst 
  

   appear. 
  

  

  While 
  the 
  otters 
  have 
  the 
  required 
  number 
  of 
  caudal 
  vertebrae 
  which 
  

   would 
  lit 
  them 
  to 
  represent 
  in 
  that 
  respect 
  the 
  type 
  from 
  which 
  the 
  

   cetaceans 
  have 
  descended, 
  the 
  assumption 
  that 
  the 
  lateral 
  integument- 
  

   ary 
  ridges 
  on 
  the 
  tail 
  of 
  Pteronura 
  might 
  be 
  exaggerated 
  by 
  gradual 
  

   evolution 
  into 
  the 
  huge 
  flukes 
  of 
  a 
  Megaptera 
  or 
  Balwna 
  is, 
  to 
  say 
  the 
  

   least, 
  far 
  less 
  satisfactory 
  than 
  the 
  hypothesis 
  that 
  these 
  structures 
  are 
  

   the 
  representatives 
  of 
  once 
  functional 
  feet. 
  Moreover, 
  the 
  first 
  traces 
  

   of 
  the 
  flukes 
  of 
  Cetacea 
  do 
  not 
  at 
  first 
  appear 
  ontogenetically, 
  as 
  they 
  

  

  * 
  Whales, 
  past 
  and 
  present, 
  and 
  their 
  probable 
  origin. 
  Nature, 
  XXVIII, 
  1883, 
  p. 
  

   229.. 
  Froni 
  a 
  lecture 
  delivered 
  before 
  the 
  Royal 
  Institution, 
  May 
  25, 
  1883. 
  

  

  