﻿[25] 
  DEVELOPMENT 
  OF 
  OSSEOUS 
  FISHES. 
  513 
  

  

  selves, 
  which 
  will 
  apparently 
  become 
  blood 
  corpuscles. 
  The 
  sinus, 
  at 
  

   any 
  rate, 
  becomes 
  much 
  crowded 
  with 
  what 
  are 
  evidently 
  blood 
  cor- 
  

   puscles. 
  Now 
  follow 
  what 
  seem 
  to 
  be 
  amoeboid 
  contractions 
  of 
  the 
  yelk, 
  

   or 
  its 
  periblastic 
  investment, 
  as 
  a 
  result 
  of 
  which 
  this 
  sinus 
  is 
  pushed 
  

   out 
  more 
  to 
  the 
  right 
  and 
  over 
  the 
  vitellus. 
  This 
  sinus, 
  as 
  it 
  is 
  further 
  

   extended, 
  in 
  a 
  girdle-like 
  manner, 
  over 
  the 
  vitellus, 
  as 
  in 
  figs. 
  22, 
  23, 
  

   and 
  24, 
  is 
  seen 
  to 
  be 
  obviously 
  homologous 
  with 
  the 
  edge 
  of 
  the 
  area 
  

   vasculosa 
  of 
  Avian 
  embryology 
  or 
  to 
  the 
  sinus 
  terminalls 
  of 
  the 
  mam- 
  

   malian 
  embryo. 
  Smaller 
  vessels 
  are 
  soon 
  formed 
  which 
  lead 
  from 
  the 
  

   under 
  side 
  of 
  the 
  posterior 
  end 
  of 
  the 
  embryo 
  and 
  join 
  the 
  great 
  mar- 
  

   ginal 
  trunk 
  anteriorly 
  which 
  leads 
  to 
  the 
  heart. 
  The 
  asymmetry 
  of 
  the 
  

   vessels 
  which 
  spread 
  over 
  the 
  yelk 
  and 
  take 
  up 
  its 
  substance 
  is 
  very 
  

   striking 
  during 
  the 
  first 
  few 
  days 
  of 
  development. 
  By 
  the 
  time 
  the 
  

   young 
  fish 
  is 
  about 
  to 
  hatch 
  the 
  marginal 
  sinus 
  or 
  trunk 
  has 
  gradually 
  

   assumed 
  a 
  median 
  position 
  on 
  the 
  under 
  side 
  of 
  the 
  yelk, 
  and 
  small 
  

   vessels 
  pass 
  out 
  on 
  either 
  side 
  of 
  the 
  body 
  on 
  the 
  upper 
  surface 
  of 
  the 
  

   yelk 
  in 
  a 
  quite 
  symmetrical 
  manner, 
  as 
  shown 
  in 
  figs. 
  25 
  and 
  2G. 
  

  

  When 
  the 
  great 
  vascular 
  sinus 
  or 
  first 
  trace 
  of 
  a 
  vascular 
  system 
  is 
  

   developed, 
  it 
  can 
  scarcely 
  be 
  said 
  that 
  there 
  is 
  a 
  circulation 
  ; 
  the 
  blood 
  

   corpuscles 
  now 
  present 
  are 
  merely 
  swayed 
  back 
  and 
  forth 
  by 
  the 
  pulsa- 
  

   tions 
  of 
  the 
  heart. 
  As 
  soon 
  as 
  the 
  aortic 
  channel, 
  underneath 
  the 
  chorda 
  

   dorsalis, 
  is 
  forced 
  through, 
  the 
  blood 
  commences 
  to 
  pour 
  through 
  the 
  

   sinus 
  from 
  the 
  tail 
  end 
  of 
  the 
  embryo 
  headward 
  over 
  the 
  yelk, 
  as 
  there 
  

   is 
  now 
  a 
  complete 
  and 
  open 
  vascular 
  cycle 
  of 
  vessels 
  developed. 
  The 
  

   cardinal 
  and 
  caudal 
  veins 
  are 
  formed 
  about 
  the 
  same 
  time. 
  From 
  them 
  

   the 
  feeders 
  of 
  the 
  sinus, 
  now 
  the 
  vitelline 
  vessels, 
  are 
  soon 
  developed, 
  

   and 
  they 
  are 
  rapidly 
  spread 
  out 
  over 
  the 
  yelk 
  as 
  narrow 
  channels, 
  be- 
  

   coming 
  more 
  and 
  more 
  numerous. 
  They 
  at 
  first 
  spread 
  out 
  over 
  the 
  

   aboral 
  pole 
  of 
  the 
  yelk, 
  and 
  a 
  great 
  common 
  venous 
  channel, 
  derived 
  

   from 
  the 
  sinus 
  first 
  mentioned, 
  begins 
  on 
  the 
  left 
  side 
  of 
  the 
  embryo 
  

   and 
  goes 
  found 
  to 
  the 
  right 
  side 
  over 
  the 
  yelk, 
  like 
  a 
  girdle, 
  to 
  feed 
  

   the 
  heart. 
  Into 
  this 
  somewhat 
  tortuous, 
  equatorial, 
  vascular 
  girdle 
  

   the 
  blood 
  pours 
  from 
  the 
  small 
  veins 
  traversing 
  the 
  yelk. 
  The 
  main 
  

   vessel 
  is 
  symmetrically 
  disposed 
  in 
  reference 
  to 
  the 
  median 
  plane 
  of 
  

   the 
  embryo, 
  and 
  is 
  gradually 
  swung 
  round 
  over 
  the 
  yelk 
  in 
  front 
  of 
  the 
  

   head 
  as 
  in 
  fig. 
  24. 
  Eventually 
  the 
  venous 
  end 
  of 
  the 
  heart 
  is 
  also 
  

   swung 
  round, 
  and 
  is 
  pushed 
  out 
  under 
  the 
  front 
  of 
  the 
  head 
  instead 
  of 
  

   extending 
  outwards 
  over 
  the 
  yelk 
  at 
  one 
  side 
  of 
  the 
  head. 
  The 
  arrange- 
  

   ment 
  and 
  changes 
  undergone 
  by 
  the 
  omphalomeseraic 
  vessels 
  of 
  the 
  

   embryo 
  stickleback 
  are 
  characteristic, 
  and 
  have 
  not 
  been 
  met 
  with, 
  as 
  

   far 
  as 
  I 
  am 
  aware, 
  in 
  the 
  embryos 
  of 
  any 
  other 
  Teleosts. 
  

  

  Kupffer's 
  vesicle 
  was 
  found 
  to 
  be 
  present. 
  The 
  urinary 
  bladder 
  

   occupies 
  the 
  usual 
  position 
  ; 
  it 
  is 
  large 
  and 
  inclosed 
  by 
  a 
  proper 
  cellular 
  

   wall. 
  The 
  course 
  of 
  the 
  intestine, 
  when 
  the 
  embryo 
  is 
  nearly 
  ready 
  to 
  

   hatch, 
  is 
  marked 
  by 
  a 
  greenish 
  color. 
  The 
  hind 
  gut, 
  during 
  the 
  earlier 
  

   stages 
  of 
  development, 
  is 
  decidedly 
  swollen 
  and 
  has 
  a 
  spacious 
  lumen. 
  

   S. 
  Mis. 
  70 
  33 
  

  

  