﻿STRUCTURE 
  AND 
  CLASSIFICATION 
  OF 
  THE 
  ARACHNIDA. 
  235 
  

  

  and 
  the 
  crab 
  are 
  the 
  only 
  two 
  invertebrates 
  which 
  had 
  

   impressed 
  the 
  minds 
  of 
  early 
  men 
  sufficiently 
  to 
  be 
  raised 
  to 
  

   the 
  dignity 
  of 
  astronomical 
  representation. 
  It 
  is 
  all 
  the 
  more 
  

   remarkable 
  that 
  the 
  scorpion 
  proves 
  to 
  be 
  the 
  oldest 
  animal 
  

   form 
  of 
  high 
  elaboration 
  which 
  has 
  persisted 
  to 
  the 
  present 
  

   day. 
  In 
  the 
  Upper 
  Silurian 
  two 
  specimens 
  of 
  a 
  scorpion 
  

   have 
  been 
  found 
  (Figs. 
  48^ 
  49), 
  one 
  in 
  Gothland 
  and 
  one 
  in 
  

   Scotland, 
  which 
  would 
  be 
  recognised 
  at 
  once 
  as 
  true 
  scorpions 
  

  

  Fig. 
  50. 
  — 
  Comparison 
  of 
  tbe 
  sixth 
  prososomatic 
  limb 
  of 
  a 
  recent 
  

   Scorpion 
  (B), 
  of 
  Palseophonus 
  (C), 
  and 
  of 
  Limulus 
  (A), 
  showing 
  

   their 
  agreement 
  in 
  the 
  number 
  of 
  segments; 
  in 
  the 
  existence 
  of 
  a 
  

   movable 
  spine, 
  Sp, 
  at 
  the 
  distal 
  border 
  of 
  fifth 
  segment; 
  in 
  the 
  

   correspondence 
  of 
  the 
  two 
  claws 
  at 
  tlie 
  free 
  end 
  of 
  the 
  limb 
  of 
  

   Scorpio 
  with 
  two 
  spines 
  similarly 
  placed 
  in 
  Limulus; 
  and, 
  lastly, 
  in 
  

   the 
  correspondence 
  of 
  the 
  three 
  talon-like 
  spines 
  carried 
  on 
  the 
  

   distal 
  margin 
  of 
  segment 
  six 
  of 
  recent 
  Scorpions 
  with 
  the 
  four 
  larger 
  

   but 
  similarly 
  situated 
  spines 
  on 
  the 
  leg 
  of 
  Limulus 
  ; 
  s, 
  groove 
  

   dividing 
  the 
  ankylosed 
  segments 
  4 
  and 
  5 
  of 
  the 
  Limulus 
  leg 
  into 
  two. 
  

   (After 
  Pocock, 
  ' 
  Quart. 
  Journ. 
  Micr. 
  Sci.,* 
  190L) 
  

  

  by 
  a 
  child 
  or 
  a 
  savage. 
  The 
  Silurian 
  scorpion, 
  Palfco- 
  

   phonus, 
  differs, 
  so 
  far 
  as 
  obvious 
  points 
  are 
  concerned, 
  from 
  

  

  