﻿490 
  REPORT 
  OF 
  COMMISSIONER 
  OP 
  PISH 
  AND 
  FISHERIES. 
  [2] 
  

  

  age, 
  as 
  held 
  by 
  Hoffmann 
  (op. 
  cit.), 
  but 
  are 
  segmented 
  off 
  from 
  the 
  

   marginal 
  cells 
  of 
  the 
  segmenting 
  blastodisk 
  as 
  suggested 
  by 
  the 
  writer 
  

   in 
  his 
  first 
  paper 
  on 
  the 
  cod. 
  

  

  With 
  the 
  further 
  growth 
  in 
  diameter 
  of 
  the 
  blastodisk 
  the 
  marginal 
  

   cells, 
  which 
  are 
  without 
  well-defined 
  outlines, 
  are 
  finally 
  covered 
  over 
  by 
  

   the 
  spreading 
  blastodisk. 
  In 
  this 
  way 
  the 
  nuclei 
  of 
  the 
  periblast 
  (a 
  

   layer 
  which 
  is 
  in 
  reality 
  a 
  syncytium) 
  are 
  finally 
  brought 
  into 
  such 
  a 
  

   position 
  that 
  they 
  seem 
  to 
  underlie 
  the 
  blastodisk. 
  The 
  nuclei 
  in 
  the 
  

   periblast 
  are, 
  however, 
  always 
  most 
  abundant 
  near 
  the 
  edge 
  of 
  the 
  blas- 
  

   todisk 
  at 
  an 
  early 
  stage 
  of 
  development. 
  During 
  the 
  later 
  stages 
  the 
  

   nuclei 
  of 
  the 
  periblast 
  are 
  most 
  numerous 
  just 
  beneath 
  the 
  embryonic 
  

   axis, 
  especially 
  under 
  the 
  head. 
  

  

  The 
  marginal 
  segmentation, 
  which 
  gives 
  rise 
  to 
  the 
  so-called 
  "free 
  nu- 
  

   clei" 
  of 
  the 
  periblast, 
  first 
  clearly 
  described 
  by 
  Agassiz 
  and 
  Whitman, 
  

   leads 
  to 
  the 
  formation 
  of 
  a 
  wreath 
  of 
  fiat 
  cells 
  which 
  form 
  a 
  more 
  or 
  

   less 
  well-marked 
  zone 
  around 
  the 
  blastoderm 
  upon 
  the 
  completion 
  of 
  

   the 
  segmentation 
  of 
  the 
  blastodisk. 
  This 
  marginal 
  wreath 
  of 
  cells, 
  " 
  nu- 
  

   clear 
  zone" 
  of 
  Kupffer, 
  has 
  been 
  figured 
  by 
  the 
  latter, 
  5 
  E. 
  Van 
  Bene 
  

   den, 
  6 
  the 
  writer, 
  7 
  Brook, 
  8 
  Cunningham, 
  9 
  and 
  by 
  Agassiz 
  and 
  Whitman. 
  

   The 
  essential 
  agreement 
  of 
  so 
  many 
  observers 
  working 
  upon 
  very 
  dif- 
  

   ferent 
  species 
  shows 
  that 
  this 
  nuclear 
  zone 
  must 
  be 
  very 
  generally 
  de 
  

   veloped 
  in 
  the 
  eggs 
  of 
  Teleosts, 
  and 
  even 
  amongst 
  the 
  Salmonidse, 
  

   where 
  it 
  is 
  not 
  so 
  easily 
  observed 
  in 
  the 
  living 
  egg, 
  but 
  which 
  is 
  shown 
  

   in 
  the 
  sections 
  figured 
  by 
  B. 
  Ziegler. 
  10 
  

  

  The 
  development 
  of 
  this 
  "nuclear 
  zone" 
  in 
  the 
  eggs 
  of 
  the 
  cod 
  es- 
  

   caped 
  my 
  observation 
  when 
  I 
  studied 
  the 
  development 
  of 
  that 
  species 
  

   in 
  1881, 
  but 
  I 
  have 
  during 
  the 
  past 
  year 
  (1885) 
  observed 
  it, 
  and 
  have, 
  

   moreover, 
  satisfied 
  myself 
  that 
  it 
  arises 
  as 
  observed 
  in 
  Ctenolabrus, 
  by 
  

   Agassiz 
  and 
  Whitman, 
  and 
  that 
  it 
  is 
  subsequently 
  covered 
  over 
  by 
  the 
  

   spreading 
  blastoderm, 
  while 
  the 
  nuclei 
  of 
  the 
  periblast, 
  also 
  subdivide 
  

   by 
  the 
  indirect 
  method, 
  and 
  proliferate 
  inwards 
  beneath 
  the 
  blastodisk. 
  

   Cunningham's 
  observations 
  are 
  in 
  accord 
  with 
  these. 
  

  

  The 
  synonymy 
  of 
  the 
  term 
  periblast 
  may 
  profitably 
  be 
  considered 
  

   here. 
  It 
  obviously 
  corresponds 
  to 
  the 
  " 
  white 
  yelk" 
  of 
  the 
  bird's 
  egg 
  ; 
  

  

  'Kupffer. 
  Beobacht. 
  ii. 
  der 
  Entw. 
  der 
  Knochenfische. 
  Arch. 
  f. 
  mikr. 
  Anat., 
  iv, 
  pi. 
  

   xvi, 
  fig. 
  1. 
  1868. 
  

  

  6 
  E. 
  Van 
  Beneden. 
  A 
  contribution 
  to 
  the 
  embryonic 
  development 
  of 
  the 
  Teleosteans. 
  

   Quar. 
  Jour. 
  Mic. 
  Sci., 
  xviii, 
  1 
  pi. 
  1878. 
  

  

  7 
  J. 
  A. 
  Ryder. 
  Development 
  of 
  the 
  Spanish 
  mackerel. 
  Bull. 
  U. 
  S. 
  Fish 
  Com., 
  i, 
  

  

  1881, 
  pp. 
  135-172, 
  pi. 
  i, 
  fig. 
  4. 
  

  

  7a 
  J. 
  A. 
  Ryder. 
  Development 
  of 
  the 
  silver 
  gar. 
  Bull. 
  U. 
  S. 
  Fish 
  Com., 
  i, 
  1881, 
  pp. 
  

   283-301, 
  pi. 
  xix, 
  fig. 
  3. 
  

  

  8 
  Brook. 
  Preliminary 
  account 
  of 
  the 
  development 
  of 
  the 
  Lesser 
  Weever-fish, 
  Trachi- 
  

   niis 
  vipera. 
  Journ. 
  Linn. 
  Soc. 
  Zool., 
  xviii, 
  1^84, 
  pp. 
  274-291, 
  pi. 
  iii, 
  figs. 
  8, 
  9-da. 
  

  

  9 
  J. 
  T. 
  Cunningham. 
  On 
  the 
  relations 
  of 
  the 
  yelk 
  to 
  the 
  gastrula 
  in 
  Teleosteans, 
  

   and 
  in 
  other 
  vertebrate 
  types. 
  Quar. 
  Jour. 
  Mic. 
  Sci., 
  1885, 
  pp. 
  38, 
  pis. 
  iv. 
  

  

  10 
  Die 
  embryonale 
  Eutwickelung 
  von 
  Salnio 
  salar. 
  Inaug. 
  Diss., 
  Freiburg 
  i, 
  B., 
  

  

  1882. 
  Taf. 
  i, 
  figs. 
  6-10. 
  

  

  