﻿2 
  EDWIN 
  S. 
  GOODIilGli. 
  

  

  vessel^ 
  and 
  running 
  to 
  the 
  perforated 
  plates 
  on 
  either 
  side 
  of 
  

   the 
  anuSj 
  through 
  which 
  they 
  reach 
  the 
  gill 
  filaments. 
  The 
  

   " 
  artery 
  '^ 
  passes 
  up 
  the 
  filament 
  to 
  the 
  tip, 
  where 
  it 
  turns 
  

   round 
  to 
  return 
  to 
  the 
  base, 
  and 
  issues 
  as 
  a 
  minute 
  ventral 
  

   "vein." 
  These 
  veins 
  are 
  collected 
  together 
  on 
  each 
  side 
  into 
  

   a 
  large 
  lateral 
  branch 
  of 
  the 
  median 
  ventral 
  vessel 
  running- 
  

   above 
  the 
  nerve-cord. 
  The 
  dorsal 
  '^ 
  arteries" 
  are 
  dis- 
  

   tinguished 
  by 
  the 
  possession 
  of 
  a 
  peculiar 
  " 
  axis," 
  formed 
  of 
  

   an 
  outer 
  sheath 
  of 
  ring-shaped 
  cells 
  with 
  regularly 
  arranged 
  

   nuclei, 
  surrounding 
  an 
  internal 
  '' 
  knorpelartiger 
  elastischer 
  

  

  Strang 
  welcher 
  aus 
  den 
  Zellen 
  zusammengesetzt 
  

  

  erscheint." 
  The 
  cells 
  of 
  this 
  inner 
  strand 
  are 
  said 
  to 
  corre- 
  

   spond 
  to 
  those 
  of 
  the 
  outer 
  sheath, 
  and 
  to 
  have 
  a 
  row 
  of 
  

   nuclei. 
  Both 
  blood-vessel 
  and 
  axis 
  are 
  described 
  as 
  sur- 
  

   rounded 
  by 
  a 
  common 
  sheath 
  of 
  peritoneal 
  epithelium. 
  The 
  

   dorsal 
  vessel 
  is 
  supposed 
  to 
  pump 
  the 
  blood 
  forwards, 
  the 
  

   circulation 
  being 
  from 
  the 
  veins 
  to 
  the 
  branchial 
  filaments, 
  

   and 
  from 
  these 
  through 
  the 
  arteries 
  to 
  the 
  dorsal 
  vessel. 
  The 
  

   gill 
  filament 
  itself 
  Vejdovsky 
  describes 
  as 
  having 
  an 
  outer 
  

   layer 
  of 
  epidermis, 
  below 
  which 
  are 
  muscles; 
  a 
  median 
  longi- 
  

   tudinal 
  septum 
  runs 
  down 
  the 
  filament 
  separating 
  two 
  

   cavities, 
  lined 
  by 
  epithelium, 
  in 
  which 
  are 
  the 
  artery 
  and 
  vein. 
  

  

  Shortly 
  after 
  the 
  appearance 
  of 
  this 
  work 
  B-ietsch 
  published 
  

   an 
  elaborate 
  account 
  of 
  the 
  vascular 
  system 
  of 
  Sternaspis 
  (4). 
  

   I 
  have 
  been 
  able 
  to 
  confirm 
  most 
  of 
  his 
  excellent 
  description. 
  

   Curiously 
  enough 
  neither 
  this 
  author 
  nor 
  Vejdovsky 
  seem 
  to 
  

   mention 
  the 
  interesting 
  horizontal 
  septum, 
  formed 
  of 
  a 
  

   double 
  layer 
  of 
  coelomic 
  epithelium 
  pierced 
  here 
  and 
  there 
  

   with 
  holes 
  (fig. 
  1, 
  hs), 
  which 
  stretches 
  across 
  the 
  posterior 
  

   region 
  of 
  the 
  coeloni 
  from 
  the 
  genital 
  ducts 
  to 
  the 
  rectum. 
  

   This 
  septum 
  supports 
  the 
  lateral 
  segmental 
  branches 
  of 
  the 
  

   ventral 
  vessel, 
  and 
  incompletely 
  separates 
  the 
  body-cavity 
  

   into 
  an 
  upper 
  chamber 
  containing 
  the 
  intestine 
  and 
  gonads, 
  

   and 
  a 
  ventral 
  chamber 
  in 
  which 
  project 
  the 
  inner 
  ends 
  of 
  the 
  

   clia3ta3 
  placed 
  round 
  the 
  ventral 
  shield, 
  and 
  the 
  nerve-cord. 
  

  

  Rietsch's 
  account 
  of 
  the 
  branchial 
  apparatus 
  is 
  less 
  satis- 
  

   factory 
  than 
  that 
  of 
  Vejdovsky. 
  According 
  to 
  the 
  former. 
  

  

  