﻿200 
  

  

  E. 
  KAY 
  LANKESTKK. 
  

  

  sinus 
  is 
  connected 
  by 
  vertical 
  muscular 
  bands 
  to 
  

   tbe 
  wall 
  of 
  the 
  ventral 
  venous 
  sinus 
  (its 
  lateral 
  ex- 
  

   pansions 
  around 
  the 
  lung-books 
  in 
  Scorpio) 
  in 
  each 
  somite 
  

   throuo'h 
  which 
  the 
  pericardium 
  passes. 
  There 
  are 
  seven 
  

   pairs 
  of 
  these 
  veno-pericardiac 
  vertical 
  muscles 
  in 
  

   Scorpio, 
  and 
  eight 
  in 
  Limulus 
  (see 
  Figs. 
  30 
  — 
  32). 
  It 
  is 
  

   obvious 
  that 
  the 
  contraction 
  of 
  these 
  muscles 
  must 
  cause 
  a 
  

   depression 
  of 
  the 
  floor 
  of 
  the 
  pericardium 
  and 
  a 
  rising 
  of 
  the 
  

   roof 
  of 
  the 
  ventral 
  blood-sinus, 
  and 
  a 
  consequent 
  increase 
  of 
  

  

  Per 
  

  

  £nta/i 
  4 
  

  

  VPM' 
  

  

  T"iG. 
  32. 
  — 
  Diagram 
  of 
  a 
  lateral 
  view 
  of 
  a 
  longitudinal 
  section 
  of 
  

   Limulus. 
  Sue, 
  suctorial 
  pharynx; 
  id, 
  alimentary 
  canal; 
  Th, 
  

   pliarynx 
  ; 
  'SI, 
  mouth 
  ; 
  Est, 
  entosternuni 
  ; 
  VS, 
  ventral 
  venous 
  sinus 
  ; 
  

   chi, 
  cliilaria 
  ; 
  go, 
  genital 
  operculum 
  ; 
  br^ 
  to 
  hr'', 
  branchial 
  append- 
  

   ages; 
  met, 
  unsegmented 
  metasoma; 
  entap*, 
  fourth 
  dorsal 
  entapo- 
  

   physis 
  of 
  left 
  side 
  ; 
  tsm, 
  ter<ro-sternal 
  muscles, 
  six 
  pairs 
  as 
  in 
  Scorpio 
  

   (labelled 
  dv 
  in 
  Fig. 
  31) 
  ; 
  TPJ/' 
  to 
  VPM^, 
  the 
  eight 
  pairs 
  of 
  veno- 
  

   pericardiac 
  muscles 
  (labelled 
  pv 
  in 
  Eig. 
  31). 
  VP^P 
  is 
  probably 
  

   represented 
  in 
  Scorpio, 
  though 
  not 
  marked 
  in 
  Figs. 
  30 
  and 
  31. 
  

   (Afler 
  Benham, 
  ' 
  Trans. 
  Zool. 
  Soc.,' 
  vol. 
  xi, 
  1S83.) 
  

  

  volume 
  and 
  flow 
  of 
  blood 
  to 
  each. 
  Whether 
  the 
  pericardium 
  

   and 
  the 
  ventral 
  sinus 
  are 
  made 
  to 
  expand 
  simultaneously 
  or 
  

   all 
  the 
  movement 
  is 
  made 
  by 
  one 
  only 
  of 
  the 
  surfaces 
  con- 
  

   cerned 
  must 
  depend 
  on 
  conditions 
  of 
  tension. 
  In 
  any 
  case 
  

   it 
  is 
  clear 
  that 
  we 
  have 
  in 
  these 
  muscles 
  an 
  apparatus 
  for 
  

   causing 
  the 
  blood 
  to 
  flow 
  differentially 
  in 
  increased 
  volume 
  

   into 
  either 
  the 
  pericardium, 
  through 
  the 
  veins 
  leading 
  from 
  

   the 
  respiratory 
  organs, 
  or 
  from 
  the 
  body 
  generally 
  into 
  the 
  

   great 
  sinuses 
  which 
  bring 
  the 
  blood 
  to 
  the 
  respiratory 
  

  

  