﻿[27] 
  DEVELOPMENT 
  OF 
  THE 
  CETACEA. 
  453 
  

  

  mal 
  mammals 
  and 
  cetaceans 
  is 
  seen 
  in 
  pinniped 
  embryos. 
  Finally, 
  

   the 
  posterior 
  lirab-folds 
  also 
  fail 
  to 
  develop 
  a 
  skeleton 
  in 
  their 
  medullary 
  

   substance. 
  

  

  Eschricht 
  (Untersuch. 
  iiocr 
  die 
  nordischen 
  Wallthiere, 
  1849, 
  p. 
  78) 
  re- 
  

   marks 
  of 
  the 
  development 
  of 
  the 
  flukes, 
  "Bei 
  ihrem 
  ersten 
  Auftreten 
  

   erscheinen 
  die 
  Schwanzfliigel 
  der 
  Cetaceen 
  als 
  zwei 
  sehrzarte 
  Hautfal- 
  

   teu 
  ganz 
  am 
  aussersteu 
  Ende 
  des 
  Schwanzes. 
  Auf 
  dieser 
  Entwicke- 
  

   luugsstufe 
  hat 
  der 
  Schwanz 
  die 
  Form 
  einer 
  kleinen 
  Lanze." 
  He 
  then 
  

   describes 
  the 
  mode 
  in 
  which 
  the 
  folds 
  rapidly 
  elongate 
  or 
  widen 
  laterally, 
  

   becoming 
  more 
  and 
  more 
  acuminate 
  and 
  longer 
  and 
  somewhat 
  falcate. 
  

   Different 
  stages 
  of 
  the 
  lobate 
  condition 
  may 
  be 
  noted 
  in 
  the 
  embryos 
  

   figured 
  in 
  the 
  plates 
  accompanying 
  this 
  paper, 
  as 
  shown 
  di 
  grammati- 
  

   cally 
  iu 
  fig. 
  15, 
  pi. 
  II. 
  

  

  Dr. 
  Jeffries 
  Wyman 
  (in 
  Proc. 
  Bost. 
  Soc. 
  Nat. 
  Hist., 
  Ill, 
  1848-'51, 
  p. 
  

   «55.*>), 
  on 
  the 
  Cth 
  of 
  November, 
  1850, 
  made 
  the 
  following 
  remarks 
  on 
  the 
  

   development 
  of 
  the 
  flukes 
  of 
  Balcena 
  mysticetus, 
  basing 
  his 
  observations 
  

   on 
  a 
  foetus 
  of 
  that 
  species, 
  G 
  inches 
  in 
  length 
  : 
  "Instead 
  of 
  the 
  long 
  flukes 
  

   and 
  central 
  depression 
  (caudal 
  notch) 
  seen 
  in 
  the 
  tail 
  of 
  the 
  adult, 
  the 
  

   tail 
  of 
  the 
  embryo 
  was 
  rounded 
  as 
  in 
  the 
  tail 
  of 
  the 
  manatee 
  ; 
  there 
  was 
  

   also 
  a 
  vertical 
  crest 
  above 
  and 
  below 
  the 
  tail." 
  

  

  Some 
  of 
  the 
  older 
  authors 
  regarded 
  the 
  flukes 
  of 
  cetaceans 
  as 
  repre- 
  

   senting 
  the 
  hinder 
  pair 
  of 
  limbs 
  in 
  normal 
  mammals, 
  such 
  expressions 
  

   as 
  " 
  cum 
  pedes 
  in 
  caudatn 
  coadunaii 
  n 
  * 
  occurriug 
  iu 
  their 
  writings, 
  by 
  

   which 
  it 
  is 
  implied 
  that 
  the 
  feet 
  have 
  been 
  fused, 
  together 
  with 
  the 
  tail, 
  

   into 
  a 
  conjoined 
  organ. 
  They 
  were 
  nearer 
  right 
  than 
  they 
  knew, 
  but 
  

   were 
  without 
  scientific 
  reasons 
  for 
  their 
  statements, 
  yet, 
  as 
  late 
  as 
  1849, 
  

   D. 
  F. 
  Eschricht 
  (op. 
  tit, 
  p. 
  78) 
  criticises 
  this 
  old 
  view 
  as 
  follows 
  and 
  

   considers 
  it 
  to 
  be 
  quite 
  untenable, 
  urging, 
  indeed, 
  that 
  when 
  the 
  ques- 
  

   tion 
  is 
  viewed 
  in 
  the 
  light 
  of 
  embryology, 
  those 
  data 
  which 
  are 
  not 
  at 
  

   least 
  unfavorable 
  to 
  such 
  an 
  interpretation 
  are 
  quite 
  insufficient 
  to 
  sus- 
  

   tain 
  it. 
  But 
  I 
  will 
  here 
  reproduce 
  his 
  remarks 
  and 
  then 
  criticise 
  them 
  

   further 
  : 
  

  

  "Die 
  Schwanzfliigel 
  der 
  Wallthiere 
  werden 
  sehr 
  allgemein 
  fiir 
  rudi- 
  

   inentare 
  Bauchgliedcr 
  angesehen, 
  wofiir 
  in 
  der 
  That 
  ihr 
  ausschliess- 
  

   liches 
  Vorkommen 
  bei 
  ihnen 
  und 
  den 
  Sireuiformien, 
  also 
  grade 
  nnr 
  bei 
  

   den 
  Saugethieren, 
  denen 
  wirkliche 
  Bauchglieder 
  abgehen, 
  sehr 
  viel 
  

   sprechen 
  kann. 
  Es 
  zeigt 
  sich 
  aber 
  diese 
  Analogie, 
  wenu 
  man 
  die 
  Ent- 
  

   wickelungsgeschichte, 
  diesen 
  Probirstein 
  der 
  anatomischen 
  Analogien, 
  

   zu 
  Hiilfe 
  zieht, 
  wo 
  nicht 
  unhaltbar, 
  doch 
  wenigstens 
  sehr 
  uuvollstandig. 
  

  

  * 
  This 
  quotation 
  is 
  from 
  the 
  Systcma 
  Natures 
  of 
  Liunteus, 
  12th 
  ed., 
  Tom. 
  I, 
  pars 
  I, 
  p. 
  

   105, 
  Holmise, 
  1767. 
  It 
  occurs 
  in 
  a 
  foot 
  note, 
  and. 
  entire 
  reads 
  as 
  follows 
  : 
  " 
  Cetis 
  qui- 
  

   busdam 
  pinna 
  dorsalis, 
  omnibus 
  pinna 
  caudce 
  et 
  jiectoralcs 
  ; 
  nullisp. 
  ani,aut 
  ventrales 
  cum 
  

   pedes 
  in 
  caudam 
  coadunali. 
  Drs. 
  Gill 
  and 
  Baur 
  have 
  called 
  rny 
  attention 
  to 
  this 
  inter- 
  

   esting 
  observation 
  hy 
  Linnaeus, 
  who, 
  however, 
  does 
  not 
  assign 
  any 
  reasons 
  for 
  his 
  

   opinion 
  as 
  expressed 
  ahove. 
  Gmeliu, 
  in 
  the 
  later 
  editions 
  of 
  the 
  Systema, 
  expunged 
  

   the 
  ahove-cited 
  foot-note. 
  

  

  