﻿-PLATE 
  IV. 
  

  

  [Tlie 
  BpecimcDB 
  represented 
  in 
  Ibis 
  Plate 
  were 
  also 
  taken 
  from 
  tbc 
  ova, 
  

   nnd 
  were 
  from 
  two 
  to 
  three 
  sixtecnlbs 
  of 
  an 
  inch 
  in 
  length.] 
  

  

  Fig 
  1 
  — 
  Showing 
  the 
  opening 
  of 
  the 
  first 
  branchial 
  vesicle 
  

   into 
  the 
  intestine, 
  (page 
  69.) 
  

  

  Fig. 
  2 
  — 
  Nearly 
  ventral 
  view 
  of 
  anterior 
  half 
  of 
  embryo, 
  

   showing 
  mouth 
  opening, 
  (page 
  70); 
  and 
  the 
  

   serai-circular 
  canals 
  of 
  the 
  car. 
  In 
  line 
  seven, 
  

   page 
  70, 
  Fig. 
  4, 
  PI. 
  IV, 
  sJioahl 
  read 
  Fig. 
  2, 
  PI. 
  

   IV. 
  All 
  the 
  other 
  organs 
  of 
  this 
  Fig. 
  are 
  more 
  

   advanced 
  than 
  in 
  the 
  other 
  figures 
  of 
  this 
  plate. 
  

  

  Fig. 
  3- 
  — 
  Very 
  much 
  enlarged 
  view 
  of 
  anterior 
  end 
  of 
  embryo, 
  

   viewed 
  nearly 
  ventrally. 
  The 
  ear 
  is 
  nearly 
  en- 
  

   closed 
  ; 
  and 
  the 
  branchial 
  slits, 
  (page 
  69,) 
  are 
  

   formed. 
  

  

  Fig. 
  4 
  — 
  An 
  earlier 
  stage 
  than 
  Fig. 
  3. 
  Three 
  of 
  the 
  bran- 
  

   chial 
  slits 
  are 
  formed 
  ; 
  the 
  heart 
  has 
  become 
  a 
  

   two-chambered 
  organ, 
  (page 
  69); 
  and 
  a 
  portion 
  

   of 
  the 
  vitellus 
  has 
  concentrated 
  into 
  a 
  large 
  oil- 
  

   sphere 
  in 
  the 
  anterior 
  part 
  of 
  the 
  yolk 
  mass, 
  (page 
  

   69.) 
  

  

  Fig. 
  6 
  — 
  Posterior 
  end 
  of 
  embryo. 
  The 
  portion 
  under 
  the 
  

   notochord 
  is 
  splitting 
  into 
  two 
  tracts, 
  in 
  which 
  

   the 
  great 
  blood-vessels 
  will 
  soon 
  be 
  formed, 
  (page 
  

  

  70.) 
  

  

  Fig. 
  6 
  — 
  Section 
  of 
  embryo 
  in 
  the 
  anal 
  region. 
  The 
  two 
  

   tracts 
  of 
  Fig. 
  5 
  are 
  seen, 
  a 
  and 
  b, 
  also 
  the 
  poste- 
  

   rior 
  end 
  of 
  the 
  intestine, 
  c, 
  (page 
  70.) 
  

  

  