﻿[35] 
  DEVELOPMENT 
  OF 
  OSSEOUS 
  FISHES. 
  523 
  

  

  ation 
  diminishes 
  greatly 
  in 
  brilliancy 
  with 
  age. 
  I 
  have 
  very 
  strong 
  

   reasons 
  to 
  suspect 
  that 
  the 
  larvae 
  of 
  this 
  species 
  are 
  phosphorescent 
  at 
  

   night. 
  

  

  XVI. 
  — 
  Gadus 
  tomcod 
  Walb. 
  {Tom-cod; 
  Frost-fish.) 
  

  

  The 
  eggs 
  of 
  this 
  species 
  of 
  Gadoid 
  are 
  somewhat 
  larger 
  than 
  those 
  

   of 
  the 
  common 
  codfish. 
  The 
  egg-membrane 
  is 
  rather 
  thick 
  and 
  tough 
  

   and 
  is 
  covered 
  externally 
  by 
  an 
  adhesive 
  coating 
  of 
  a 
  mucine-like 
  sub- 
  

   stance 
  which 
  agglutinates 
  the 
  eggs 
  together 
  in 
  masses, 
  the 
  latter 
  being 
  

   very 
  frequently, 
  if 
  not 
  usually, 
  attached 
  to 
  sea- 
  weeds 
  and 
  stones 
  at 
  the 
  

   bottom 
  of 
  the 
  littoral 
  zone. 
  The 
  eggs 
  are 
  not 
  pelagic, 
  like 
  those 
  of 
  the 
  

   cod, 
  though 
  there 
  is 
  a 
  very 
  conspicuous 
  oil-drop 
  in 
  the 
  vitellus 
  ; 
  as 
  de- 
  

   velopment 
  progresses 
  this 
  oil-drop 
  is 
  pushed 
  forward 
  to 
  the 
  anterior 
  

   pole 
  of 
  the 
  yelk-sack. 
  

  

  When 
  hatched 
  the 
  gape 
  of 
  the 
  mouth 
  is 
  very 
  much 
  greater 
  than 
  that 
  

   of 
  the 
  larva 
  of 
  the 
  common 
  cod. 
  The 
  intestine 
  terminates 
  at 
  the 
  margin 
  

   of 
  the 
  ventral 
  fin-fold, 
  instead 
  of 
  some 
  distance 
  from 
  it, 
  as 
  in 
  the 
  larval 
  

   cod, 
  as 
  may 
  be 
  seen 
  by 
  comparing 
  figs. 
  1 
  and 
  07. 
  There 
  is 
  no 
  integu- 
  

   mentary 
  vesicle 
  or 
  bulla 
  developed 
  over 
  the 
  head 
  as 
  in 
  the 
  young 
  cod, 
  

   so 
  that 
  the 
  larval 
  stages 
  of 
  this 
  species 
  differ 
  very 
  widely 
  from 
  its 
  con- 
  

   gener, 
  though 
  both 
  spawn 
  in 
  winter 
  or 
  during 
  the 
  colder 
  months 
  of 
  the 
  

   year. 
  The 
  larvas 
  of 
  the 
  tomcod 
  are 
  also 
  more 
  robust 
  in 
  build 
  than 
  

   those 
  of 
  the 
  cod, 
  and 
  measure 
  at 
  the 
  time 
  of 
  hatching 
  very 
  nearly, 
  if 
  

   not 
  quite, 
  5 
  mm 
  in 
  length. 
  

  

  XVII.— 
  Clupea 
  sapidissima 
  Wilson. 
  {The 
  Common 
  Shad.) 
  

  

  The 
  interest 
  attaching 
  to 
  the 
  development 
  of 
  this 
  species 
  is 
  two-fold, 
  

   namely, 
  that 
  which 
  appeals 
  to 
  the 
  economist 
  and 
  that 
  which 
  appeals 
  

   to 
  the 
  biologist. 
  While 
  the 
  description 
  of 
  the 
  morphological 
  changes 
  

   which 
  this 
  species 
  undergoes 
  during 
  development 
  will 
  be 
  of 
  immediate 
  

   interest 
  only 
  to 
  the 
  latter, 
  the 
  former, 
  if 
  he 
  be 
  a 
  fish-culturist, 
  and 
  not 
  

   otherwise 
  interested 
  in 
  the 
  life-history 
  of 
  the 
  type 
  under 
  consideration, 
  

   may 
  still 
  perhaps 
  derive 
  useful 
  information 
  from 
  what 
  is 
  to 
  follow 
  re- 
  

   specting 
  the 
  maimer 
  in 
  which 
  the 
  perpetuation 
  and 
  development 
  of 
  this 
  

   valuable 
  food-fish 
  is 
  accomplished. 
  With 
  the 
  invention 
  of 
  greatly 
  im- 
  

   proved 
  appliances, 
  the 
  hatching 
  of 
  this 
  form 
  from 
  artificially 
  fertilized 
  

   eggs 
  is 
  now 
  accomplished 
  to 
  the 
  number 
  of 
  perhaps 
  fifty 
  to 
  seventy 
  

   millions 
  annually 
  along 
  the 
  Atlantic 
  slope, 
  reckoning 
  in 
  this 
  total 
  the 
  

   combined 
  efforts 
  of 
  the 
  United 
  States 
  and 
  the 
  different 
  State 
  fish 
  com- 
  

   missions 
  of 
  the 
  coastwise 
  States. 
  The 
  species 
  is 
  anadromous 
  and 
  quite 
  

   fertile, 
  a 
  single 
  female 
  yielding 
  during 
  the 
  season, 
  if 
  unmolested, 
  about 
  

   200,000 
  ova. 
  These 
  ova 
  are 
  probably 
  discharged 
  in 
  shoal 
  water 
  and 
  

   mainly 
  after 
  night-fall. 
  Spawning 
  occurs 
  during 
  the 
  spring 
  months 
  of 
  

   April 
  and 
  May, 
  and 
  as 
  late 
  as 
  June 
  and 
  July 
  in 
  the 
  latitude 
  of 
  Wash- 
  

   ington 
  and 
  Baltimore. 
  

  

  