﻿[51] 
  DEVELOPMENT 
  OF 
  OSSEOUS 
  FISHES. 
  539 
  

  

  nearly 
  horizontal 
  position. 
  The 
  young 
  Ictalurus 
  is 
  now 
  twenty 
  days 
  

   old 
  and 
  would 
  be 
  readily 
  recognized 
  as 
  possibly 
  belonging 
  to 
  one 
  of 
  

   several 
  American 
  genera, 
  though 
  at 
  this 
  stage 
  it 
  resembles 
  most 
  nearly 
  

   the 
  adult 
  of 
  the 
  genus 
  AToturus, 
  indicating 
  that 
  the 
  latter 
  is 
  a 
  less 
  

   specialized 
  type 
  than 
  the 
  one 
  here 
  under 
  consideration. 
  

  

  When 
  the 
  young 
  Ictalurus 
  is 
  eighty-eight 
  days 
  old, 
  as 
  shown 
  in 
  figs. 
  

   171 
  and 
  172, 
  from 
  the 
  side 
  and 
  from 
  above, 
  its 
  external 
  generic 
  fea- 
  

   tures 
  become 
  distinctly 
  apparent. 
  The 
  anterior 
  dorsal 
  spine 
  and 
  the 
  

   pectoral 
  spines, 
  armed 
  posteriorly 
  with 
  recurved 
  hooks, 
  are 
  now 
  devel- 
  

   oped. 
  The 
  post-scapular 
  process 
  is 
  evident 
  beneath 
  the 
  skin 
  and 
  tbe 
  

   air 
  bladder 
  forms 
  a 
  strongly 
  marked 
  rounded 
  prominence 
  just 
  behind 
  

   the 
  shoulder 
  girdle, 
  where 
  it 
  presses 
  the 
  body- 
  wall 
  outwards. 
  The 
  soft 
  

   dorsal 
  is 
  now 
  quite 
  free 
  and 
  sharply 
  defined 
  posteriorly, 
  and 
  the 
  pig- 
  

   mentation, 
  which 
  has 
  gradually 
  increased 
  in 
  depth 
  since 
  the 
  time 
  of 
  

   hatching, 
  is 
  now 
  very 
  nearly 
  that 
  of 
  the 
  adult. 
  At 
  this 
  stage 
  of 
  devel- 
  

   opment 
  the 
  young 
  fish 
  measures 
  lO.o 
  111111 
  in 
  length. 
  At 
  the 
  end 
  of 
  one 
  

   hundred 
  and 
  twelve 
  days 
  theyouug 
  of 
  Ictalurus, 
  measures 
  25 
  mm 
  in 
  length, 
  

   or 
  about 
  1 
  inch. 
  When 
  one 
  hundred 
  and 
  seventy 
  days 
  old 
  the 
  young 
  

   fish 
  measures 
  35 
  uim 
  in 
  length. 
  These 
  two 
  stages 
  I 
  have 
  not 
  figured, 
  since 
  

   the 
  resemblance 
  to 
  the 
  adults 
  is 
  sufficiently 
  obvious 
  in 
  fig. 
  171, 
  repre- 
  

   senting 
  a 
  much 
  younger 
  individual. 
  The 
  young 
  of 
  Ictalurus 
  therefore 
  

   more 
  than 
  double 
  their 
  length 
  in 
  eighty-two 
  days, 
  and 
  nearly 
  quadruple 
  

   it 
  in 
  one 
  hundred 
  and 
  sixty-four 
  days 
  after 
  hatching, 
  as 
  the 
  foregoing 
  

   data 
  demonstrate. 
  

  

  On 
  the 
  fifteenth 
  day 
  after 
  oviposition 
  it 
  was 
  found 
  that 
  the 
  young 
  fishes 
  

   would 
  feed. 
  While 
  discussing 
  with 
  the 
  writer 
  what 
  should 
  be 
  provided 
  

   for 
  them 
  Mr. 
  J. 
  E. 
  Brown 
  threw 
  some 
  pieces 
  of 
  fresh 
  liver 
  into 
  the 
  

   aquarium, 
  which 
  they 
  devoured 
  with 
  avidity. 
  It 
  was 
  now 
  evident 
  that 
  

   they 
  were 
  provided 
  with 
  teeth, 
  as 
  they 
  would 
  pull 
  and 
  tug 
  at 
  the 
  frag- 
  

   ments 
  of 
  liver 
  with 
  the 
  most 
  dogged 
  perseverance 
  and 
  apparent 
  feroc- 
  

   ity. 
  This 
  experiment 
  showed 
  that 
  the 
  right 
  kind 
  of 
  food 
  had 
  been 
  sup- 
  

   plied, 
  and 
  as 
  they 
  were 
  then 
  fed, 
  up 
  to 
  August 
  1, 
  with 
  nothing 
  else 
  with- 
  

   out 
  our 
  losing 
  a 
  single 
  one 
  of 
  the 
  brood, 
  nothing 
  more 
  in 
  the 
  way 
  of 
  

   food 
  seemed 
  to 
  be 
  required. 
  

  

  It 
  is 
  worthy 
  of 
  note 
  that 
  when 
  pieces 
  of 
  liver 
  were 
  thrown 
  into 
  the 
  

   aquarium 
  the 
  parent 
  fish 
  would 
  apparently 
  often 
  swallow 
  them, 
  with 
  

   numbers 
  of 
  his 
  offspring 
  eating 
  at 
  and 
  hanging 
  to 
  such 
  fragments. 
  I 
  

   was 
  soon 
  agreeably 
  surprised 
  to 
  find 
  that 
  the 
  parent 
  fish 
  swallowed 
  

   only 
  the 
  meat, 
  and 
  that 
  he 
  invariably 
  ejected 
  the 
  young 
  fish 
  from 
  the 
  

   mouth 
  uninjured, 
  as 
  he 
  seemed 
  to 
  be 
  able 
  to 
  discriminate, 
  instinctively 
  

   and 
  before 
  deglutition 
  occurred, 
  between 
  what 
  was 
  his 
  proper 
  food 
  and 
  

   what 
  were 
  his 
  own 
  young. 
  As 
  soon 
  as 
  the 
  young 
  began 
  to 
  feed 
  they 
  

   commenced 
  to 
  disperse 
  through 
  the 
  water 
  and 
  to 
  all 
  parts 
  of 
  the 
  aqua- 
  

   rium, 
  and 
  to 
  manifest 
  less 
  desire 
  to 
  congregate 
  in 
  schools 
  near 
  the 
  male, 
  

   who 
  also 
  abated 
  his 
  habit 
  of 
  fanning 
  the 
  young 
  with 
  his 
  fins, 
  as 
  was 
  his 
  

   wont 
  during 
  the 
  early 
  phases 
  of 
  development, 
  

  

  