﻿XIX 
  -ON 
  THE 
  DEVELOPMENT 
  OF 
  THE 
  CETACEA, 
  TOGETHER 
  

   WITH 
  A 
  CONSIDERATION 
  OF 
  THE 
  PROBABLE 
  HOMOLOGIES 
  OF 
  

   THE 
  FLUKES 
  OF 
  CETACEANS 
  AND 
  SIRENIANS.* 
  

  

  By 
  John 
  A. 
  Ryder. 
  

  

  TABLE 
  OF 
  CONTENTS. 
  

  

  Paga 
  

  

  Introductory 
  1 
  

  

  I. 
  — 
  The 
  contrasts 
  between 
  the 
  marine, 
  amphibious, 
  and 
  terrestrial 
  mam- 
  

   malia 
  3 
  

  

  II. 
  — 
  Development 
  23 
  

  

  III. 
  — 
  The 
  hypertrophy 
  and 
  differentiation 
  of 
  the 
  cau 
  dal 
  vertebrae 
  of 
  Cetaceans 
  

  

  into 
  two 
  series 
  30 
  

  

  IV. 
  — 
  Degeneracy 
  of 
  the 
  pelvic 
  girdle 
  and 
  hind 
  limbs 
  in 
  Cetacea 
  33 
  

  

  V. 
  — 
  The 
  caudal 
  muscles 
  of 
  Cetacea 
  38 
  

  

  VI. 
  — 
  The 
  lumbo-caudal 
  plexus 
  of 
  nerves 
  in 
  Cetaceans 
  43 
  

  

  VII. 
  —The 
  translocation 
  of 
  the 
  distal 
  ends 
  of 
  the 
  hind-limbs 
  in 
  the 
  Sirenians. 
  49 
  

   VIII. 
  — 
  On 
  what 
  appear 
  to 
  be 
  tactile 
  hairs 
  or 
  vibrissse 
  in 
  Cetaceans 
  and 
  Sire- 
  

   nians 
  - 
  - 
  54 
  

  

  IX.— 
  Summary 
  56 
  

  

  INTRODUCTORY. 
  

  

  The 
  acquisition 
  of 
  materials 
  for 
  the 
  prosecution 
  of 
  the 
  study 
  of 
  Ceta- 
  

   cean 
  development 
  is 
  attended 
  with 
  difficulties, 
  and 
  the 
  student 
  who 
  is 
  

   fortunate 
  enough 
  to 
  have 
  access 
  to 
  a 
  rare 
  series 
  of 
  even 
  pretty 
  well 
  ad- 
  

   vanced 
  embryos, 
  measuring 
  from 
  1 
  inch 
  up 
  to 
  5£ 
  inches 
  long, 
  may 
  well 
  

   consider 
  how 
  precious 
  and 
  important 
  such 
  materials 
  are 
  at 
  this 
  time, 
  

   when 
  the 
  study 
  of 
  the 
  development 
  of 
  living 
  forms 
  has 
  taken 
  such 
  a 
  

   high 
  place 
  as 
  a 
  part 
  of 
  the 
  proper 
  scientific 
  method 
  to 
  be 
  applied 
  by 
  

   the 
  naturalist 
  to 
  the 
  resolution 
  of 
  questions 
  of 
  affinity 
  and 
  the 
  genesis 
  

   of 
  extreme 
  structural 
  modifications. 
  

  

  The 
  following 
  notes, 
  interspersed 
  as 
  they 
  will 
  be 
  with 
  reflections 
  

  

  *A 
  very 
  brief 
  and 
  imperfect 
  sketch 
  of 
  the 
  contents 
  of 
  this 
  paper 
  has 
  appeared 
  under 
  

   the 
  following 
  title: 
  "On 
  the 
  probable 
  origin, 
  homologies, 
  and 
  development 
  of 
  the 
  

   flukes 
  of 
  Cetaceans 
  and 
  Sirenians." 
  (Am. 
  Naturalist, 
  May, 
  1885, 
  pp. 
  515-519.) 
  The 
  

   development 
  of 
  the 
  mammary 
  glands 
  has 
  also 
  been 
  more 
  fully 
  discussed 
  by 
  me 
  else- 
  

   where, 
  viz, 
  in 
  a 
  paper 
  entitled, 
  " 
  On 
  the 
  development 
  of 
  the 
  mammary 
  glands 
  and 
  

   genitalia 
  of 
  the 
  Cetacea." 
  (Bull. 
  United 
  States 
  Fish 
  Commission, 
  Vol. 
  V, 
  1885.) 
  

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  427 
  

  

  