﻿STRUCTURE 
  AND 
  CLASSIFICATION 
  OF 
  THE 
  ARACHNIDA. 
  167 
  

  

  by 
  the 
  demoustration 
  that 
  Limulus 
  and 
  the 
  extinct 
  Eury- 
  

   pterines 
  (Pterygotus^ 
  etc.) 
  are 
  Arachnida 
  ; 
  that 
  is 
  to 
  say, 
  are 
  

   identical 
  in 
  the 
  structure 
  and 
  relation 
  of 
  so 
  many 
  important 
  

   parts 
  with 
  Scorpio, 
  whilst 
  differing 
  in 
  those 
  respects 
  from 
  

   other 
  Arthropoda 
  that 
  it 
  is 
  impossible 
  to 
  suppose 
  that 
  the 
  

   identity 
  is 
  due 
  to 
  homoplasy 
  or 
  convergence, 
  and 
  the 
  con- 
  

  

  FiG. 
  3. 
  

  

  Fig. 
  4. 
  

  

  -BR. 
  

  

  pf..... 
  

  

  m 
  

  

  AC. 
  

  

  Fig. 
  3. 
  — 
  Entosternuni 
  of 
  Scorpion 
  (Palamnceus 
  indus, 
  De 
  

   Geer) 
  ; 
  dorsal 
  surface, 
  asp, 
  paired 
  anterior 
  process 
  of 
  the 
  sub- 
  

   neural 
  arch; 
  snp, 
  sub-neural 
  arch 
  ; 
  ap, 
  anterior 
  lateral 
  process 
  (same 
  

   as 
  RAP 
  and 
  LAP 
  in 
  Fig. 
  1); 
  Imp, 
  lateral 
  median 
  process 
  (same 
  as 
  

   ALR 
  and 
  PLR 
  of 
  Fijr. 
  1) 
  ; 
  pp, 
  posterior 
  process 
  (same 
  as 
  PhP 
  in 
  

   Fig'. 
  1); 
  /j/, 
  posterior 
  flap 
  or 
  diaphragm 
  of 
  Newport; 
  m^ 
  and 
  m-, 
  

   perforations 
  of 
  tlie 
  diaphragm 
  for 
  the 
  passage 
  of 
  muscles; 
  LR, 
  the 
  

   paired 
  dorsal 
  ridges; 
  GC, 
  gastric 
  canal 
  or 
  foramen; 
  AG, 
  arterial 
  

   canal 
  or 
  foramen. 
  Magnified 
  five 
  times 
  linear. 
  (After 
  Lankester, 
  

   loc. 
  cit.) 
  

  

  Fig. 
  4. 
  — 
  Ventral 
  surface 
  of 
  the 
  same 
  entosternum 
  as 
  that 
  drawn 
  

   in 
  Fig. 
  3. 
  Letters 
  as 
  in 
  Fig. 
  3 
  with 
  the 
  addition 
  of 
  NC, 
  neural 
  

   canal 
  or 
  foramen. 
  (After 
  Lankester, 
  loc. 
  cit.) 
  

  

  elusion 
  must 
  be 
  accepted 
  that 
  the 
  resemblances 
  arise 
  from 
  

   close 
  genetic 
  relationship. 
  The 
  view 
  that 
  Limulus, 
  the 
  king- 
  

   crab, 
  is 
  an 
  Arachnid 
  was 
  maintained 
  as 
  long 
  ago 
  as 
  1829 
  by 
  

   Straus-Dui'kheim 
  (1), 
  on 
  the 
  ground 
  of 
  its 
  possession 
  of 
  an 
  

   internal 
  cartilaginous 
  sternum 
  — 
  also 
  possessed 
  by 
  the 
  Arach- 
  

   nida 
  (see 
  Figs. 
  1 
  — 
  6), 
  — 
  and 
  of 
  the 
  similarity 
  of 
  the 
  disposition 
  

   of 
  the 
  six 
  leg-like 
  appendages 
  around 
  the 
  mouth 
  in 
  the 
  two 
  

  

  