﻿8 
  EDWIN 
  S. 
  GOODRIOH. 
  

  

  aud 
  may 
  subdivide 
  so 
  tliat 
  one 
  minute 
  vessel 
  goes 
  to 
  eacli 
  

   filament. 
  Since 
  only 
  two 
  vessels 
  are 
  found 
  in 
  each 
  gill 
  

   filamentj 
  and 
  three 
  can 
  be 
  traced 
  to 
  its 
  base, 
  it 
  becomes 
  an 
  

   interesting 
  matter 
  to 
  determine 
  what 
  becomes 
  of 
  the 
  third. 
  

   This 
  is 
  the 
  point 
  which 
  1 
  found 
  so 
  difficult 
  to 
  settle. 
  

  

  Whilst 
  it 
  is 
  comparatively 
  easy 
  to 
  follow 
  the 
  dorsal 
  

   branchial 
  vessel 
  aud 
  its 
  accompanying 
  communicating 
  vessel 
  

   to 
  the 
  base 
  of 
  a 
  gill 
  filament, 
  it 
  is 
  very 
  difficult 
  indeed 
  to 
  trace 
  

   the 
  course 
  of 
  the 
  ventral 
  capillary 
  vessel. 
  These 
  blood- 
  

   vessels 
  are 
  too 
  minute 
  to 
  inject 
  or 
  to 
  follow 
  for 
  certain 
  by 
  dis- 
  

   section. 
  Sections 
  taken 
  through 
  the 
  regions 
  where 
  the 
  

   vessels 
  pass 
  through 
  the 
  branchial 
  plate 
  show 
  that 
  as 
  a 
  

   matter 
  of 
  fact 
  the 
  communicating 
  vessel 
  joins 
  the 
  ventral 
  

   branchial 
  vessel 
  quite 
  near 
  the 
  body-wall 
  to 
  form 
  a 
  single 
  

   vessel 
  entering 
  the 
  gill. 
  Figs. 
  10 
  and 
  11 
  show 
  this 
  com- 
  

   munication 
  clearly, 
  whilst 
  the 
  relation 
  of 
  the 
  three 
  sets 
  of 
  

   vessels 
  to 
  the 
  gills 
  is 
  represented 
  diagrammatically 
  in 
  fig. 
  8. 
  

  

  The 
  reason 
  for 
  this 
  peculiar 
  arrangement 
  is 
  not 
  far 
  to 
  seek. 
  

   Supposing 
  there 
  existed 
  only 
  a 
  dorsal 
  " 
  artery 
  " 
  and 
  a 
  venti'al 
  

   "vein/' 
  as 
  described 
  by 
  previous 
  authors, 
  it 
  is 
  obvious 
  that 
  

   on 
  the 
  retraction 
  of 
  the 
  gill 
  filaments 
  the 
  whole 
  circulation 
  of 
  

   the 
  blood 
  would 
  be 
  almost 
  entirely 
  stopped. 
  By 
  means 
  of 
  

   the 
  communicating 
  vessel 
  the 
  blood 
  has 
  in 
  such 
  a 
  case 
  

   an 
  alternative 
  path 
  open 
  to 
  it 
  leading 
  from 
  the 
  

   main 
  ventral 
  to 
  the 
  main 
  dorsal 
  vessel. 
  A 
  somewhat 
  

   similar 
  by-path 
  for 
  the 
  blood 
  is 
  present 
  at 
  tlie 
  base 
  of 
  the 
  re- 
  

   tractile 
  gills 
  of 
  the 
  Urodele 
  amphibians, 
  and 
  serves 
  no 
  doubt 
  

   the 
  same 
  purpose. 
  

  

  Concerning 
  the 
  circulation 
  of 
  the 
  blood 
  in 
  the 
  living 
  Ster- 
  

   naspis, 
  I 
  feel 
  by 
  no 
  means 
  certain 
  that 
  the 
  direction 
  of 
  the 
  

   flow 
  is 
  from 
  the 
  ventral 
  vessel 
  to 
  the 
  dorsal 
  vessel 
  through 
  the 
  

   branchial 
  filaments, 
  as 
  held 
  by 
  Vejdovsky 
  and 
  Kietsch. 
  The 
  

   disposition 
  of 
  the 
  valves 
  and 
  certain 
  contractions 
  in 
  freshly 
  

   dissected 
  specimens 
  lead 
  me 
  to 
  believe 
  that 
  the 
  blood 
  is 
  pro- 
  

   pelled 
  along 
  the 
  contractile 
  dorsal 
  branchial 
  vessels 
  from 
  

   before 
  backwards. 
  However, 
  this 
  is 
  a 
  subject 
  which 
  requires 
  

   further 
  study. 
  

  

  