﻿494 
  EEPORT 
  OF 
  COMMISSIONER 
  OP 
  FISH 
  AND 
  FISHERIES. 
  [6] 
  

  

  cells" 
  from 
  the 
  edge 
  of 
  the 
  blastodisk. 
  And 
  contrary 
  to 
  what 
  some 
  of 
  

   the 
  more 
  recen 
  t 
  writers 
  on 
  Teleostean 
  development 
  would 
  seem 
  to 
  imply, 
  

   I 
  had 
  already 
  suggested 
  that 
  the 
  nuclear 
  zone 
  gave 
  rise 
  to 
  the 
  nuclei 
  of 
  

   the 
  periblast, 
  as 
  the 
  following 
  quotation 
  will 
  show: 
  "The 
  free 
  nuclei 
  

   of 
  the 
  yelk-hypoblast 
  apparently 
  proliferate 
  as 
  the 
  blastoderm 
  spreads. 
  

   They 
  are, 
  at 
  any 
  rate, 
  at 
  first 
  confined 
  to 
  the 
  germinal 
  pole 
  of 
  the 
  

   ovum, 
  and 
  are 
  only 
  found 
  at 
  the 
  opposite 
  pole 
  after 
  the 
  yelk-globe 
  has 
  

   been 
  included 
  by 
  the 
  blastoderm. 
  The 
  inference, 
  therefore, 
  is 
  that 
  they 
  

   spread 
  and 
  multiply 
  with 
  the 
  lateral 
  growth 
  of 
  the 
  blastoderm. 
  It 
  is 
  

   these 
  nuclei 
  possibly 
  which 
  are 
  the 
  centers 
  of 
  certain 
  free 
  cells 
  around 
  

   the 
  margin 
  of 
  the 
  germinal 
  disk 
  when 
  the 
  latter 
  has 
  attained 
  the 
  morula 
  

   stage, 
  as 
  in 
  Cybium 
  and 
  Tylosurus, 
  as 
  shown 
  in 
  fig. 
  3, 
  pi. 
  six, 
  of 
  my 
  

   essay 
  on 
  the 
  latter 
  form. 
  If 
  such 
  is 
  the 
  case, 
  it 
  is 
  possible 
  that 
  the 
  

   germinal 
  wall 
  (Eeimwall) 
  at 
  the 
  edge 
  of 
  the 
  blastoderm 
  of 
  the 
  chick 
  is 
  

   homologous 
  with 
  the 
  yelk-hypoblast 
  of 
  the 
  fish 
  ovum" 
  (Contr. 
  Embryog. 
  

   Oss. 
  Fishes, 
  p. 
  509). 
  

  

  The 
  marginal 
  inflection 
  of 
  the 
  blastodisk 
  is 
  figured 
  by 
  Kingsley 
  and 
  

   Conn 
  (No. 
  14) 
  in 
  Ctenolabr2is, 
  and 
  by 
  Brook, 
  16 
  1T 
  as 
  being 
  composed 
  of 
  

   larger 
  cells 
  than 
  that 
  of 
  the 
  epiblast. 
  Kingsley 
  and 
  Conn 
  represent 
  

   only 
  a 
  single 
  layer 
  in 
  Ctenolabrus, 
  a 
  condition 
  which 
  1 
  have 
  never 
  

   found 
  to 
  exist 
  in 
  sections 
  of 
  the 
  disks 
  of 
  any 
  of 
  the 
  species 
  studied 
  by 
  

   me. 
  Brook 
  represents 
  several 
  layers 
  of 
  larger 
  cells 
  in 
  the 
  hypoblast. 
  

   That 
  the 
  inferior 
  stratum 
  of 
  cells 
  of 
  the 
  inflected 
  hypoblastic 
  layer 
  are 
  

   perhaps 
  somewhat 
  larger 
  than 
  those 
  of 
  the 
  epiblast 
  I 
  admit, 
  but 
  that 
  

   they 
  are 
  generally 
  very 
  much 
  larger 
  or 
  that 
  the 
  inflected 
  hypoblast 
  is 
  

   ever 
  formed 
  of 
  a 
  single 
  layer, 
  as 
  held 
  by 
  Kingsley 
  and 
  Conn, 
  I 
  am 
  dis- 
  

   posed 
  to 
  question. 
  

  

  Cunuiiiiiham 
  (On 
  the 
  relation 
  of 
  the 
  yelk 
  to 
  the 
  gastrula 
  in 
  Teleos- 
  

   teans, 
  etc..) 
  has 
  studied 
  the 
  development 
  of 
  three 
  Gadoid 
  forms, 
  and 
  has 
  

   been 
  the 
  hist 
  English 
  iuvestigator 
  who 
  has 
  declared 
  himself 
  an 
  advo- 
  

   cate 
  of 
  the 
  concrescence 
  theory, 
  which, 
  in 
  its 
  various 
  forms, 
  has 
  been 
  

   supported 
  by 
  His, 
  13 
  Bauber, 
  19 
  Whitman, 
  20 
  and 
  myself, 
  21 
  and 
  latterly 
  by 
  

   Duval 
  22 
  and 
  Kollmann. 
  

  

  16 
  Brook. 
  On 
  some 
  points 
  in 
  the 
  development 
  of 
  Motella 
  mustela 
  L. 
  Journ. 
  Linn. 
  

   Soc.Zool.,xviii, 
  Nov., 
  1884, 
  pp. 
  298-307, 
  pis. 
  viii-x. 
  

  

  17 
  Brook. 
  On 
  the 
  origin 
  of 
  the 
  hypoblast 
  in 
  pelagic 
  Teleostean 
  ova. 
  Quar. 
  Journ. 
  

   Mic. 
  Sci., 
  Jan., 
  1885, 
  pi. 
  iii. 
  

  

  18 
  W. 
  His. 
  Ueher 
  die 
  Bildung 
  der 
  Haifischembryonen. 
  Zeitschr. 
  f. 
  Anat. 
  u. 
  

   Eutwickelungesch.,ii, 
  1877, 
  pis. 
  vii; 
  also, 
  Untersuch. 
  lib. 
  die 
  Entwick. 
  von 
  Kuochen- 
  

   tische, 
  etc., 
  in 
  vol. 
  i 
  of 
  same 
  journal, 
  1 
  pi. 
  

  

  lw 
  Rauber. 
  Primitifstreifeu 
  und 
  Neurula 
  ; 
  also, 
  Die 
  Theorien 
  der 
  excessiven 
  Moustra, 
  

   Virchow's 
  Archiv. 
  lxxi, 
  1877, 
  pis. 
  3. 
  

  

  20 
  Whitman. 
  Embryology 
  of 
  Clepsine. 
  Quar. 
  Jour. 
  Mic. 
  Sci., 
  July, 
  1878, 
  pp. 
  101, 
  

   pis. 
  xii-xv. 
  

  

  21 
  Ryder. 
  Ou 
  the 
  formation 
  of 
  the 
  embryonic 
  axis 
  of 
  the 
  Teleostean 
  embryo 
  by 
  the 
  

   concrescence 
  of 
  the 
  rim 
  of 
  the 
  blastoderm. 
  Am. 
  Naturalist, 
  1885, 
  pp. 
  (514-615, 
  1 
  fig. 
  

  

  22 
  Mathias 
  Duval. 
  De 
  la 
  formation 
  du 
  blastoderme 
  dans 
  l'ceuf 
  d'oiseau. 
  Ann. 
  Sci. 
  

   Naturelles. 
  Zool., 
  6 
  e 
  ser., 
  tome 
  xviii, 
  pp. 
  208, 
  pis. 
  5, 
  1884. 
  

  

  