﻿518 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [30] 
  

  

  agglutinating 
  matter 
  which, 
  covered 
  the 
  zona 
  radiata 
  seemed 
  to 
  have 
  

   flowed 
  down 
  over 
  the 
  egg 
  aud 
  hardened 
  into 
  a 
  kind 
  of 
  flat 
  disk 
  at 
  one 
  

   side, 
  as 
  shown 
  in 
  fig. 
  31. 
  The 
  yelk 
  is 
  quite 
  transparent, 
  but 
  the 
  disk 
  

   and 
  blastoderm 
  are 
  rather 
  thick; 
  these 
  characters 
  lead 
  me 
  to 
  think 
  

   that 
  it 
  is 
  the 
  egg 
  either 
  of 
  a 
  Cyprinoid 
  or 
  a 
  Centrarchid, 
  most 
  probably 
  

   the 
  latter, 
  as. 
  the 
  yelk 
  of 
  the 
  Cyprinoids 
  is 
  generally 
  very 
  granular. 
  

  

  XI. 
  — 
  Perca 
  Americana 
  Schranck. 
  (Yellow 
  Perch; 
  American 
  or 
  

  

  Ringed 
  Perch.) 
  

  

  I 
  have 
  not 
  yet 
  had 
  an 
  opportunity 
  to 
  study 
  the 
  development 
  of 
  this 
  

   valuable 
  fresh-water 
  species, 
  which 
  spawns 
  in 
  April 
  and 
  May. 
  Like 
  the 
  

   European 
  P. 
  flnviatilis, 
  it 
  lays 
  its 
  eggs 
  in 
  flat 
  bands 
  consisting 
  of 
  a 
  sin- 
  

   gle 
  layer, 
  agglutinated 
  together 
  by 
  an 
  adhesive 
  material. 
  These 
  flat 
  

   bands 
  of 
  eggs 
  somewhat 
  resemble 
  those 
  of 
  the 
  goose-fish 
  or 
  Lophius. 
  

   but 
  they 
  are 
  not 
  as 
  large 
  and 
  do 
  not 
  float 
  on 
  the 
  surface 
  as 
  do 
  the 
  egg- 
  

   ribbons 
  of 
  the 
  latter; 
  on 
  the 
  contrary, 
  in 
  this 
  species, 
  they 
  are 
  quite 
  

   heavy 
  and 
  sink 
  to 
  the 
  bottom, 
  and 
  are 
  suspended 
  by 
  the 
  female 
  in 
  all 
  

   probability 
  upon 
  submerged 
  objects 
  where 
  they 
  are 
  left 
  to 
  hatch 
  out. 
  

  

  The 
  envelopes 
  of 
  the 
  eggs 
  of 
  the 
  yellow 
  perch 
  are, 
  however, 
  so 
  com- 
  

   plex 
  in 
  structure 
  that 
  they 
  may 
  be 
  recognized 
  with 
  the 
  greatest 
  readi- 
  

   ness. 
  The 
  vitellus 
  measures 
  1.75 
  mm 
  in 
  diameter. 
  It 
  contains 
  a 
  large 
  

   oil-sphere 
  which 
  occupies 
  an 
  eccentric 
  position. 
  The 
  oil-sphere 
  is 
  not 
  

   represented 
  in 
  fig. 
  35, 
  plate 
  viii, 
  representing 
  the 
  egg 
  of 
  the 
  Ameri- 
  

   can 
  perch, 
  which 
  measures, 
  including 
  the 
  spacious 
  and 
  thick-walled 
  

   egg-membrane, 
  3.5 
  mni 
  in 
  total 
  diameter. 
  

  

  The 
  egg-membrane 
  is 
  exceedingly 
  complex, 
  and 
  consists 
  apparently 
  

   of 
  an 
  internal 
  layer, 
  z, 
  which 
  is 
  homologous 
  with 
  the 
  zona 
  radiata 
  of 
  

   other 
  types. 
  Immediately 
  overlying 
  the 
  zona 
  there 
  is 
  a 
  very 
  thick, 
  

   highly 
  elastic 
  layer, 
  g, 
  which 
  is 
  traversed 
  radially 
  by 
  fibers 
  or 
  canals 
  

   which 
  widen 
  perceptibly 
  at 
  the 
  outer 
  surface. 
  A 
  third 
  thin 
  investment, 
  

   a, 
  overlies 
  this 
  thick 
  elastic 
  layer, 
  and 
  it 
  consists 
  of 
  the 
  hardened 
  mucine- 
  

   like 
  material 
  which 
  agglutinates 
  the 
  eggs 
  together. 
  At 
  one 
  point 
  on 
  

   the 
  surface 
  of 
  the 
  egg 
  there 
  is 
  a 
  wider 
  pore 
  canal 
  which 
  leads 
  to 
  the 
  mi- 
  

   cropyle 
  m. 
  The 
  outer 
  layer, 
  a, 
  serves 
  to 
  agglutinate 
  the 
  egg 
  to 
  the 
  outer 
  

   layer 
  of 
  adjacent 
  eggs, 
  as 
  shown 
  in 
  fig. 
  35. 
  

  

  XII. 
  — 
  Rocctrs 
  americanus 
  (Gmel.) 
  J. 
  & 
  G. 
  ( 
  White 
  Perch.) 
  

  

  The 
  eggs 
  of 
  this 
  species 
  are 
  quite 
  small 
  and 
  measure 
  only 
  about 
  .73 
  nim 
  

   or 
  one 
  thirty-fourth 
  of 
  an 
  inch 
  in 
  diameter, 
  are 
  very 
  adhesive 
  and 
  stick 
  

   together 
  in 
  masses 
  or 
  in 
  thin 
  layers 
  over 
  fixed 
  objects 
  in 
  the 
  water. 
  

   The 
  zona 
  radiata 
  is 
  quite 
  thick 
  and 
  is 
  traversed 
  by 
  fine 
  pore-canals. 
  

   The 
  micropyle 
  is 
  a 
  minute 
  opening 
  measuring 
  .0075 
  mm 
  in 
  diameter. 
  

   Externally 
  the 
  zona 
  radiata 
  is 
  at 
  first 
  covered 
  by 
  a 
  thick 
  layer 
  of 
  ad- 
  

   hesive 
  matter, 
  which 
  flows 
  toward 
  the 
  points 
  where 
  the 
  eggs 
  come 
  into 
  

  

  