﻿STRtJOTLFRE 
  AND 
  CLASSIFICATION 
  OF 
  THE 
  ARACHNIDA. 
  199 
  

  

  comes 
  nearer 
  to 
  Limulus 
  in 
  tlie 
  high 
  development 
  of 
  its 
  

   arterial 
  system, 
  and 
  the 
  intimate 
  relation 
  of 
  the 
  anterior 
  

   aorta 
  and 
  its 
  branches 
  to 
  the 
  nerve 
  centres 
  and 
  great 
  nerves, 
  

   than 
  does 
  any 
  other 
  Arthropod. 
  

  

  An 
  arrangement 
  of 
  great 
  fnuctional 
  importance 
  in 
  regard 
  

   to 
  the 
  venous 
  system 
  must 
  now 
  be 
  described, 
  which 
  was 
  

   shown 
  in 
  1883 
  by 
  Lankester 
  to 
  be 
  common 
  to 
  Limulus 
  and 
  

   Scorpio. 
  This 
  arrangement 
  has 
  not 
  hitherto 
  been 
  detected 
  

   in 
  any 
  other 
  class 
  than 
  the 
  Arachnida, 
  and 
  if 
  it 
  should 
  

   ultimately 
  prove 
  to 
  be 
  peculiar 
  to 
  that 
  group, 
  would 
  have 
  

  

  ram 
  ri 
  '^^^ 
  P 
  j 
  , 
  \^.-<a. 
  > 
  

   dv' 
  ^r^^rfv 
  

   sliq 
  

  

  Fig. 
  31. 
  — 
  Diagram 
  of 
  a 
  lateral 
  view 
  of 
  a 
  longitudinal 
  section 
  of 
  a 
  

   Scorpion, 
  d, 
  clielicera; 
  ch, 
  chela; 
  ^<z/;/, 
  camerostome 
  ; 
  m, 
  mouth; 
  

   ent, 
  entosternum 
  ; 
  p, 
  pecteu 
  ; 
  slig'^, 
  first 
  pulmonary 
  aperture; 
  stig^, 
  

   fourth 
  pulmonary 
  aperture; 
  dam, 
  muscle 
  from 
  carapace 
  toaprseoral 
  

   entosclerite 
  ; 
  ad, 
  muscle 
  from 
  carapace 
  to 
  entosternum; 
  md, 
  muscle 
  

   from 
  tergite 
  of 
  genital 
  somite 
  to 
  entosternum 
  (same 
  as 
  dpm 
  in 
  Fig. 
  

   30) 
  ; 
  </«' 
  to 
  dv^, 
  dorso-ventral 
  muscles 
  (same 
  as 
  the 
  series 
  labelled 
  

   tsm 
  in 
  Fig. 
  30) 
  ; 
  pv^ 
  to 
  pv'^, 
  the 
  seven 
  veno-pericardiac 
  muscles 
  of 
  

   the 
  right 
  side 
  (labelled 
  VPM 
  in 
  Fig. 
  30). 
  (After 
  Beck, 
  'Trans. 
  

   Zool. 
  Soc.,' 
  vol. 
  xi, 
  1S83.) 
  

  

  considerable 
  weight 
  as 
  a 
  proof 
  of 
  the 
  close 
  genetic 
  aflSnity 
  of 
  

   Limulus 
  and 
  Scorpio. 
  

  

  The 
  great 
  pericardial 
  sinus 
  is 
  strongly 
  developed 
  in 
  both 
  

   animals. 
  Its 
  walls 
  are 
  fibrous 
  and 
  complete, 
  and 
  it 
  holds 
  a 
  

   considerable 
  volume 
  of 
  blood 
  when 
  the 
  heart 
  itself 
  is 
  con- 
  

   tracted. 
  Opening 
  in 
  pairs 
  in 
  each 
  somite, 
  right 
  and 
  left 
  

   into 
  the 
  pericai'dial 
  sinus 
  are 
  large 
  veins, 
  which 
  bring 
  the 
  

   blood 
  respectively 
  from 
  the 
  gill-books 
  and 
  the 
  lung-books 
  to 
  

   that 
  chambei', 
  Avhence 
  it 
  passes 
  by 
  the 
  ostia 
  into 
  the 
  heart. 
  

   The 
  blood 
  is 
  brought 
  to 
  the 
  respiratory 
  organs 
  in 
  both 
  cases 
  

   by 
  a 
  great 
  venous-collecting 
  sinus 
  having 
  a 
  ventral 
  median 
  

   position. 
  In 
  both 
  animals 
  the 
  wall 
  of 
  the 
  pericardial 
  

  

  