﻿576 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [88] 
  

  

  EXPLANATION 
  OF 
  PLATE 
  XVI. 
  

  

  Clupea 
  sapidissima. 
  {The 
  Common 
  Shad.) 
  

  

  Fig. 
  101. 
  An 
  embryo 
  shad, 
  somewhat 
  older 
  than 
  the 
  stage 
  represented 
  in 
  section 
  in 
  

   fig. 
  98, 
  in 
  its 
  natural 
  position 
  in 
  its 
  spacions 
  enveloping 
  membrane. 
  From 
  a 
  

   photograph. 
  

  

  Fig. 
  102. 
  An 
  embryo 
  of 
  the 
  same 
  age 
  drawn 
  without 
  details, 
  and 
  showing 
  the 
  position 
  

   of 
  Kupffer's 
  vesicle 
  at 
  lev, 
  and 
  the 
  heart 
  h. 
  

  

  Fig. 
  103. 
  A 
  still 
  more 
  advanced 
  embryo, 
  showing 
  the 
  hind 
  gut 
  hg 
  just 
  under 
  the 
  out- 
  

   growing 
  tail. 
  

  

  Fig. 
  104. 
  Cross-section 
  through 
  the 
  budding 
  tail 
  of 
  an 
  embryo 
  of 
  the 
  preceding 
  stage, 
  

   showing 
  the 
  relations 
  of 
  the 
  muscle 
  plates 
  m 
  m 
  to 
  the 
  nervous 
  cord 
  N, 
  the 
  chorda 
  ch, 
  

   and 
  the 
  post-anal 
  section 
  of 
  the 
  intestine 
  i. 
  The 
  median 
  fin-folds 
  are 
  still 
  quite 
  

   rudimentary, 
  and 
  are 
  developed 
  as 
  very 
  slight, 
  ridge-like 
  folds 
  of 
  the 
  skin 
  above 
  

   and 
  below 
  in 
  the 
  median 
  line. 
  

  

  Fig. 
  105. 
  A 
  similar 
  cross-section 
  of 
  an 
  embryo 
  of 
  the 
  same 
  age, 
  somewhat 
  farther 
  for- 
  

   ward. 
  

  

  Figs. 
  106 
  and 
  107. 
  Cross-sections 
  through 
  the 
  body 
  of 
  an 
  embryo 
  somewhat 
  younger 
  

   than 
  that 
  represented 
  in 
  fig. 
  102. 
  The 
  hypoblastic 
  layer 
  has 
  not 
  yet 
  been 
  differ- 
  

   entiated 
  into 
  the 
  intestine 
  at 
  i. 
  The 
  nervous 
  cord 
  JVis 
  still 
  continuous 
  with 
  the 
  

   epiblast 
  e 
  of 
  the 
  embryo. 
  The 
  chorda 
  ch 
  and 
  muscle 
  plates 
  have 
  been 
  differen- 
  

   tiated. 
  

  

  Fig. 
  108. 
  A 
  similar 
  cross-section 
  through 
  the 
  anterior 
  part 
  of 
  the 
  trunk 
  of 
  an 
  embryo 
  

   of 
  the 
  same 
  age 
  as 
  that 
  from 
  which 
  the 
  preceding 
  sections 
  were 
  prepared. 
  

  

  Figs. 
  109, 
  110, 
  111, 
  and 
  112. 
  Four 
  cross-sections 
  through 
  different 
  regions 
  of 
  the 
  body 
  

   cavity 
  of 
  a 
  much 
  more 
  advanced 
  embryo, 
  the 
  first 
  being 
  the 
  most 
  anterior. 
  The 
  

   nervous 
  cord 
  N 
  is 
  detached 
  from 
  the 
  skin, 
  the 
  segmental 
  ducts 
  are 
  well 
  denned, 
  

   and 
  the 
  intestine 
  i 
  has 
  a 
  narrow 
  lumen. 
  

  

  Fig. 
  113. 
  Diagrammatic 
  representation 
  of 
  an 
  embryo 
  of 
  about 
  the 
  age 
  of 
  the 
  one 
  rep- 
  

   resented 
  in 
  fig. 
  103, 
  but 
  unrolled 
  from 
  the 
  vitellus, 
  to 
  show 
  the 
  course 
  of 
  the 
  

   segmental 
  ducts 
  sd 
  and 
  the 
  extension 
  outward 
  of 
  the 
  pectoral 
  plates 
  pp, 
  which 
  

   are 
  intimately 
  concerned 
  in 
  the 
  development 
  of 
  the 
  pectoral 
  fins. 
  

  

  