﻿458 
  REPORT 
  OF 
  COMMISSIONER 
  OP 
  PISH 
  AND 
  FISHERIES. 
  [32] 
  

  

  lated 
  to 
  each 
  other 
  as 
  to 
  origin 
  through 
  a 
  remote 
  common 
  ancestry. 
  

   It 
  is 
  nevertheless 
  difficult 
  to 
  understand 
  the 
  way 
  in 
  which 
  the 
  caudal 
  

   musculature 
  of 
  the 
  Cetacea 
  has 
  been 
  developed 
  with 
  the 
  concomitant 
  

   differentiation 
  of 
  the 
  caudal 
  vertebra? 
  into 
  an 
  anterior 
  and 
  posterior 
  

   series, 
  unless 
  it 
  be 
  supposed 
  that, 
  as 
  the 
  flukes 
  become 
  more 
  or 
  less 
  

   rigid 
  the 
  posterior 
  vertebra? 
  included 
  between 
  their 
  bases 
  would 
  tend 
  

   to 
  degenerate, 
  whereas 
  the 
  anterior 
  series 
  of 
  vertebra; 
  would 
  tend 
  to 
  

   develop 
  in 
  proportion 
  to 
  their 
  functional 
  importance 
  as 
  a 
  substitute 
  for 
  

   the 
  skeleton 
  of 
  the 
  hind 
  limbs. 
  This 
  still 
  leaves 
  the 
  question 
  as 
  to 
  the 
  

   origin 
  of 
  the 
  degenerate 
  caudal 
  vertebra? 
  of 
  the 
  pinnipeds 
  unanswered 
  

   and 
  brings 
  us 
  face 
  to 
  face 
  with 
  au 
  aspect 
  of 
  the 
  question 
  which 
  does 
  

   seem 
  to 
  throw 
  some 
  light 
  upon 
  this 
  phase 
  of 
  the 
  subject. 
  I 
  hardly 
  

   think 
  any 
  naturalist 
  will 
  dispute 
  the 
  conclusion 
  that 
  a 
  mammalian 
  type 
  

   could 
  have 
  originated 
  anywhere 
  else 
  than 
  on 
  land 
  in 
  order 
  to 
  success- 
  

   fully 
  develop 
  its 
  air-breathing 
  and 
  characteristic 
  modifications 
  of 
  struct- 
  

   ure. 
  Such 
  a 
  conclusion 
  carries 
  with 
  it 
  the 
  implication 
  that 
  the 
  whales 
  

   have 
  been 
  derived 
  from 
  laud 
  forms, 
  as 
  seems 
  indeed 
  to 
  be 
  conclusively 
  

   proved 
  by 
  the 
  adult 
  anatomy 
  and 
  especially 
  tbe 
  presence 
  of 
  certain 
  

   structures 
  which 
  are 
  on 
  the 
  way 
  to 
  complete 
  atrophy. 
  In 
  land 
  mam- 
  

   mals, 
  however, 
  the 
  tail 
  is 
  in 
  reality 
  always 
  degenerate 
  and 
  often 
  quite 
  

   as 
  much 
  so 
  as 
  in 
  the 
  seals, 
  for 
  no 
  matter 
  how 
  long 
  the 
  tail 
  may 
  be, 
  if 
  

   the 
  diameter 
  of 
  its 
  base 
  is 
  far 
  less 
  than 
  that 
  through 
  the 
  pelvic 
  region 
  

   immediately 
  in 
  front 
  of 
  its 
  base, 
  we 
  may 
  be 
  certain 
  that 
  degeneracy 
  

   from 
  the 
  primordial 
  type, 
  as 
  seen 
  in 
  fishes, 
  amphibians, 
  and 
  some 
  rep- 
  

   tiles, 
  has 
  occurred. 
  In 
  the 
  last-mentioned 
  types 
  there 
  is 
  no 
  such 
  abrupt 
  

   distinction 
  between 
  the 
  trunk 
  and 
  tail 
  as 
  in 
  land 
  mammals. 
  The 
  infer- 
  

   ence, 
  therefore, 
  is 
  that 
  the 
  tail 
  of 
  cetaceans, 
  though 
  probably 
  derived 
  

   from 
  oue 
  in 
  which 
  there 
  were 
  more 
  vertebral 
  segments 
  than 
  are 
  found 
  

   in 
  the 
  tail 
  of 
  any 
  existing 
  pinniped, 
  has 
  been 
  developed 
  from 
  that 
  of 
  

   a 
  land 
  mammal 
  in 
  which 
  the 
  tail 
  was 
  already 
  degenerate 
  and 
  of 
  com- 
  

   paratively 
  little 
  functional 
  importance, 
  just 
  as 
  we 
  have 
  seen 
  is 
  the 
  case 
  

   in 
  the 
  seals. 
  

  

  The 
  difficulty 
  which 
  seemed 
  to 
  present 
  itself 
  in 
  regard 
  to 
  the 
  degen- 
  

   eracy 
  of 
  the 
  pinniped 
  tail, 
  therefore 
  also 
  disappears, 
  and 
  a 
  new 
  question 
  

   arises, 
  viz 
  : 
  How 
  was 
  the 
  gradual 
  muscular 
  degeneracy 
  of 
  the 
  hind 
  limbs 
  

   of 
  our 
  ideal 
  protocetacean 
  form 
  related 
  to 
  the 
  increasing 
  functional 
  im- 
  

   portance 
  of 
  the 
  tail 
  with 
  a 
  gradual 
  new 
  development 
  of 
  muscle 
  over 
  a 
  

   region 
  where 
  it 
  had 
  been 
  once 
  before 
  lost, 
  in 
  the 
  course 
  of 
  the 
  evolution 
  

   of 
  the 
  mammalian 
  type? 
  The 
  answer 
  to 
  this, 
  it 
  seems 
  to 
  me, 
  has 
  been 
  

   already 
  given, 
  but 
  it 
  may 
  be 
  well 
  to 
  discuss 
  it 
  anew 
  in 
  another 
  form. 
  

  

  As 
  the 
  fish-like 
  form 
  of 
  the 
  hind 
  part 
  of 
  the 
  pinniped's 
  body 
  became 
  

   more 
  pronounced 
  as 
  a 
  result 
  of 
  advancing 
  inclusion, 
  we 
  saw 
  that 
  the 
  

   hyposkeletal 
  flexors 
  of 
  the 
  back 
  part 
  of 
  the 
  trunk 
  became 
  more 
  devel- 
  

   oped. 
  With 
  increasing 
  enfeeblement 
  of 
  the 
  hind 
  limbs 
  the 
  caudal 
  skele- 
  

   ton 
  and 
  musculature 
  would 
  become 
  stronger, 
  indeed 
  the 
  oue 
  would 
  

   gradually 
  exchange 
  functions.with 
  the 
  other, 
  so 
  that 
  no 
  violent 
  or 
  sudden 
  

  

  