﻿[9] 
  DEVELOPMENT 
  OF 
  OSSEOUS 
  FISHES. 
  497 
  

  

  dition 
  of 
  the 
  vesicle 
  in 
  a 
  larva 
  just 
  hatched 
  and 
  figured 
  on 
  plate 
  ii 
  of 
  

   the 
  paper 
  cited. 
  At 
  that 
  time 
  I 
  named 
  the 
  space 
  in 
  the 
  supracephalic 
  

   vesicle 
  of 
  the 
  Spanish 
  mackerel, 
  the 
  " 
  supracephalic 
  sinus." 
  Now. 
  while 
  

   it 
  is 
  clear 
  that 
  this 
  sinus 
  is 
  the 
  houiologue 
  of 
  the 
  ranch 
  larger 
  one 
  in 
  the 
  

   larvae 
  of 
  Gadus, 
  it 
  is 
  also 
  clear 
  that 
  in 
  the 
  latter 
  it 
  extends 
  not 
  alone 
  

   over 
  the 
  brain 
  as 
  in 
  Scomberomorus, 
  but 
  even 
  back 
  dorsally 
  beyond 
  the 
  

   hinder 
  limits 
  of 
  the 
  body 
  cavity. 
  

  

  I 
  have 
  good 
  reasons 
  for 
  believing 
  that 
  a 
  sinus 
  of 
  the 
  same 
  character 
  

   overlies 
  the 
  brain 
  in 
  a 
  number 
  of 
  the 
  species 
  figured 
  by 
  A. 
  Agassiz 
  and 
  

   his 
  associate 
  Whitman 
  as 
  well 
  as 
  in 
  the 
  Lirvse 
  of 
  Trachinus 
  and 
  Motella 
  

   figured 
  by 
  Brook. 
  In 
  fact, 
  I 
  doubt 
  if 
  the 
  structure 
  represented 
  in 
  advance 
  

   of 
  the 
  first 
  developed 
  dorsal 
  fin-ray 
  on 
  the 
  head 
  of 
  the 
  larva 
  of 
  Lophivs 
  

   by 
  A. 
  Agassiz 
  27 
  is 
  a 
  fin 
  -fold 
  at 
  all, 
  but 
  merely 
  the 
  integumentary 
  vesicle 
  

   or 
  bulla 
  described 
  above, 
  though 
  the 
  contrary 
  is 
  expressly 
  stated 
  on 
  

   page 
  282 
  of 
  the 
  memoir 
  last 
  cited. 
  A 
  still 
  more 
  remarkable 
  instance 
  of 
  

   the 
  extension 
  apparently 
  backward 
  and 
  laterally 
  of 
  what 
  I 
  have 
  called 
  

   the 
  "supracephalic 
  sinus" 
  is 
  represented 
  however 
  by 
  Agassiz 
  and 
  Whit- 
  

   man 
  on 
  plate 
  xii, 
  figs. 
  7 
  and 
  8, 
  of 
  their 
  recent 
  memoir 
  (Pelagic 
  stages 
  

   of 
  young 
  fishes, 
  part 
  I, 
  4to, 
  1885). 
  In 
  this 
  form 
  the 
  sinus 
  has 
  been 
  ex- 
  

   tended 
  back 
  for 
  two 
  thirds 
  of 
  the 
  length 
  of 
  the 
  larva 
  and 
  also 
  over 
  the 
  

   sides 
  of 
  the 
  head. 
  The 
  form 
  in 
  question 
  is 
  supposed 
  by 
  its 
  describers 
  

   to 
  be 
  near 
  Motella. 
  

  

  It 
  is 
  therefore 
  probable, 
  taking 
  into 
  account 
  the 
  facts 
  recited 
  above, 
  

   that 
  the 
  true, 
  median, 
  dorsal 
  fin-fold 
  is 
  never 
  extended 
  as 
  far 
  forward 
  

   as 
  the 
  front 
  of 
  the 
  head, 
  as 
  J 
  had 
  assumed 
  in 
  my 
  paper 
  cited 
  above 
  on 
  

   the 
  development 
  of 
  the 
  median 
  fins, 
  but 
  that 
  such 
  an 
  apparent 
  anterior 
  

   dorsal 
  extension 
  of 
  the 
  fin-fold 
  is 
  due 
  to 
  the 
  illusion 
  produced 
  by 
  the 
  

   extreme 
  transparency 
  of 
  the 
  integument 
  of 
  the 
  dorsal 
  vesicle 
  or 
  bulla 
  

   just 
  described, 
  the 
  presence 
  of 
  which 
  is 
  not 
  easily 
  made 
  out 
  until 
  the 
  

   living 
  embryo 
  is 
  viewed 
  from 
  in 
  front. 
  The 
  true 
  median 
  fin-fold 
  in 
  the 
  

   larvae 
  of 
  Gadus 
  is 
  therefore 
  but 
  little 
  longer 
  proportionally 
  than 
  that 
  of 
  

   other 
  types 
  of 
  larvae 
  which 
  are 
  without 
  a 
  supracephalic 
  bulla. 
  The 
  

   archaic 
  extension 
  of 
  the 
  fin 
  folds 
  in 
  fishes 
  therefore, 
  it 
  seems, 
  must 
  have 
  

   been 
  about 
  the 
  same 
  as 
  that 
  generally 
  prevalent 
  to-day 
  in 
  young 
  larvae, 
  

   or 
  an 
  extension 
  of 
  the 
  fin-folds 
  which 
  is 
  most 
  nearly 
  approximated 
  by 
  

   such 
  adult 
  forms 
  as 
  the 
  Dipnoi. 
  

  

  The 
  contents 
  of 
  the 
  bulla 
  or 
  sinus 
  have 
  been 
  but 
  little 
  studied, 
  but 
  it 
  

   is 
  probable, 
  judging 
  from 
  certain 
  observations 
  upon 
  the 
  contents 
  of 
  the 
  

   fin-folds 
  of 
  larval 
  fishes 
  by 
  Emery, 
  28 
  that 
  this 
  bulla 
  in 
  Gadus 
  contains 
  

   coagulable 
  albumen. 
  I 
  have 
  found 
  such 
  a 
  coagulum 
  Li 
  the 
  fin-folds 
  of 
  

   hardened 
  embryos 
  of 
  Clupea. 
  And 
  in 
  embryos 
  of 
  Scomberomorus 
  I 
  found 
  

   loose 
  granular 
  matter 
  in 
  the 
  sinus 
  on 
  the 
  top 
  of 
  the 
  head 
  and 
  fin-folds. 
  

  

  27 
  A. 
  Agassiz. 
  On 
  the 
  young 
  stages 
  of 
  osseous 
  fishes. 
  Part 
  iii, 
  Proc. 
  Am. 
  Acad. 
  

   Arts 
  and 
  Sci., 
  xvii, 
  1882, 
  pis. 
  xvi, 
  xvii. 
  

  

  28 
  Emery. 
  Sulla 
  existenza 
  del 
  eosidetoo 
  tessuto 
  di 
  secretioiie 
  nei 
  vertebrati. 
  Atti 
  

   E. 
  Acad. 
  Sci., 
  Torino, 
  xviii, 
  1883. 
  

  

  S. 
  Mis. 
  70 
  32 
  

  

  