﻿ON 
  THI'] 
  BBANCHLAL 
  VESSELS 
  OF 
  STERNASPIS. 
  3 
  

  

  the 
  branchial 
  vessels 
  '^ 
  se 
  composent 
  d'liii 
  axe 
  conjonctif 
  et 
  

   d'uu 
  vaisseau 
  paralleles 
  et 
  enveloppes 
  dans 
  une 
  gaine 
  com- 
  

   mune." 
  Further, 
  " 
  Faxe 
  se 
  compose 
  d'nne 
  serie 
  d'anneaux 
  

   enveloppant 
  un 
  cylindre 
  fibreiix. 
  Le 
  dernier 
  est 
  constitue 
  

   par 
  des 
  fibres 
  longitudinales 
  munies 
  de 
  noyaux 
  allonges 
  " 
  

   (4). 
  On 
  the 
  whole 
  Riotsch's 
  Interpretation 
  of 
  the 
  structure 
  

   of 
  these 
  vessels 
  is 
  very 
  much 
  the 
  same 
  as 
  Vejdovsky's; 
  but 
  

   he 
  believes 
  the 
  " 
  axis 
  " 
  to 
  be 
  continuous 
  behind 
  with 
  the 
  

   epidermis, 
  of 
  which 
  it 
  is 
  considered 
  to 
  be 
  a 
  prolongation. 
  

   He 
  is 
  not 
  clear 
  as 
  to 
  the 
  exact 
  relation 
  of 
  the 
  dorsal 
  and 
  

   ventral 
  branchial 
  vessels 
  to 
  the 
  filaments. 
  Rietsch, 
  indeed, 
  

   is 
  not 
  certain 
  that 
  the 
  ventral 
  vessels 
  enter 
  the 
  gills 
  at 
  all, 
  

   and 
  believes 
  that 
  they 
  may 
  only 
  supply 
  the 
  body-wall, 
  

   pointing 
  out 
  that 
  they 
  are 
  fewer 
  in 
  number 
  than 
  the 
  dorsal 
  

   " 
  arteries.'^ 
  He 
  denies 
  the 
  contractility 
  of 
  the 
  main 
  dorsal 
  

   vessel, 
  and 
  suggests 
  that 
  the 
  blood 
  may 
  be 
  propelled 
  by 
  the 
  

   lengthening 
  and 
  shortening 
  of 
  the 
  axis 
  supporting 
  the 
  

   " 
  arteries." 
  The 
  gill 
  filament 
  is 
  said 
  by 
  him 
  to 
  contain 
  only 
  

   one 
  vessel, 
  and 
  the 
  cavity 
  not 
  to 
  be 
  lined 
  by 
  peritoneum. 
  

  

  In 
  answer 
  to 
  Rietsch, 
  who 
  criticised 
  his 
  work, 
  Vejdovsky 
  

   published 
  a 
  second 
  more 
  detailed, 
  but 
  scarcely 
  more 
  correct, 
  

   account 
  of 
  these 
  complicated 
  organs 
  (6). 
  Here 
  the 
  branchial 
  

   "veins" 
  are 
  accurately 
  described 
  and 
  figured; 
  the 
  ''axis" 
  

   of 
  the 
  branchial 
  "arteries" 
  is 
  said 
  to 
  consist 
  "aus 
  

   einer 
  hyalineu, 
  bindegewebigen 
  Substanz 
  .... 
  an 
  dessen 
  

   Wandung 
  in 
  zierlicher 
  Anordnung 
  vielfach 
  verastelte 
  Zellen 
  

   gelagert 
  sind," 
  surrounded 
  by 
  contractile 
  " 
  Halbriugen 
  " 
  

   covered 
  with 
  an 
  outer 
  hyaline 
  sheath 
  of 
  cells 
  with 
  large 
  

   nuclei 
  situated 
  in 
  a 
  row. 
  

  

  As 
  ali-eady 
  mentioned, 
  according 
  to 
  my 
  own 
  observations, 
  

   the 
  structure 
  of 
  the 
  branchial 
  apparatus 
  differs 
  considei-ably 
  

   from 
  that 
  described 
  by 
  these 
  authors. 
  

  

  The 
  slender 
  outer 
  gill 
  filaments, 
  as 
  is 
  well 
  known, 
  are 
  

   capable 
  of 
  independent 
  movement, 
  and 
  may 
  be 
  quickly 
  

   retracted 
  into 
  a 
  closely 
  coiled 
  spiral 
  (see 
  4, 
  5, 
  and 
  3, 
  fig. 
  16; 
  

   also 
  PI. 
  1, 
  fig. 
  8). 
  Two 
  small 
  blood-vessels 
  run 
  along 
  each 
  

   filament, 
  and 
  join 
  at 
  the 
  extreme 
  tip 
  (fig. 
  2). 
  These 
  vessels 
  

  

  